connecting rod strength h vs I beam

[grumpyvette]

you might want to read thru these links for info also
first lets point out how you calculate 4000 Feet Per Minute, in piston speed, which in most chevy v8 engines is a reasonable durability limit
in one revolution a piston moves from TDC (top dead center )TO BDC (bottom dead center)and back to TDC, so you calculate the distance traveled as twice the stroke, and 4000 feet per minute is 12" per minute times the rpms
but anyone who understands engines understands that piston speed and rod bolt stress are far from the only factors limiting an engine rotational speed, most valve trains in stock engines, and valve springs and cam lobe acceleration rates are limited to about 5800rpm-6200rpm, and air flow rates or port stall speed could very easily limit power, as can a restrictive exhaust, an ignition systems, rpm limitations or a lube system, not being able to keep up with demand

thus if you have a 3" stroke, 4000 fpm=48,000 inches divided by 6"=8000rpm red line in theory, for piston speed, on something like a 283 sbc

thus if you have a 4" stroke 4000 fpm=48,000 inches divided by 8"=6000rpm red line in theory,for piston speed,
on something like a 454 bbc

READ THESE LINKS
viewtopic.php?f=53&t=1168

http://www.superchevy.com/how-to/engine ... m#cxrecs_s


if you care to get into the math and engineering, heres some linked info

I went thru years of this in college and still get head aches thinking about the math

https://www.forging.org/system/files/fi ... alysis.pdf

http://www.hotrod.com/techarticles/hrdp ... ting_rods/

http://emweb.unl.edu/Mechanics-Pages/Lu ... s%20VI.htm

http://www.iosrjournals.org/iosr-jmce/p ... df?id=7622

http://www.ijsrp.org/research-paper-021 ... -p1479.pdf

http://www.eng.utoledo.edu/mime/faculty ... 15-624.pdf

http://victorylibrary.com/mopar/rod-tech-c.htm
viewtopic.php?f=53&t=341

viewtopic.php?f=53&t=510

http://www.rustpuppy.org/rodstudy.htm

http://www.iskycams.com/techtips.html#2005

http://www.hotrod.com/techarticles/gene ... ting_rods/

viewtopic.php?f=53&t=10213

viewtopic.php?f=53&t=3540&p=9395#p9395

http://www.compstarcomponents.com/connecting_rods.htm

http://victorylibrary.com/mopar/rod-tech-c.htm

http://www.rehermorrison.com/techtalk/63.htm

http://www.youtube.com/watch?v=uTpRfREYa9Q

http://www.chevy-camaro.com/parts/chevy ... onnect.htm

http://www.hotrod.com/techarticles/stee ... index.html

http://www.youtube.com/watch?v=hp931tDlHoU&feature=fvw

http://emweb.unl.edu/Mechanics-Pages/Lu ... s%20VI.htm

https://www.lunatipower.com/Category.aspx?id=13

http://www.youtube.com/watch?v=H2YrL3k__dA

http://www.youtube.com/watch?v=hp931tDlHoU&feature=fvw

http://www.hcs.harvard.edu/~jus/0303/kuo.pdf

http://www.scatcrankshafts.com/index.htm

http://www.hotrod.com/techarticles/stee ... index.html

viewtopic.php?f=53&t=247

http://emweb.unl.edu/Mechanics-Pages/Lu ... s%20VI.htm

http://www.tomei-p.co.jp/_2003web-catal ... onrod.html

http://www.enginebuildermag.com/Article ... oices.aspx

http://www.youtube.com/watch?v=uTpRfREYa9Q

http://www.youtube.com/watch?v=hp931tDlHoU&NR=1

http://www.youtube.com/watch?v=cJJI9bml ... re=related

IF YOU LOOK CLOSELY AT ALMOST EVERY (CONNECTING ROD) thats failed in almost every engine Ive ever seen or read about its almost never the rod itself, that failed but its the bolts, that stretched or bearings ., lack of lubrication or the cause is trying to compress a bent valve, or busted piston due to some factor like detonation.
I generally use and suggest use of scat 4340 forged cranks or occasionally the 9000 cast steel scat cranks for daily driver applications, SCAT, usually does a good job of carefully checking crank dimensions but its your job to check clearances , anytime you build an engine its the builders responsibility to verify clearances, and youll almost always find a rotating assembly needs to be balanced, obviously the crank manufacturer can,t dictate what rods, pistons,piston pins, rings, damper or flywheel are used so the crank counter weights won,t be perfectly balanced
and any decent engineer could design EITHER an (H) or (I) beam rod to have exactly the same material cross sectional area, whats important is the strength too weight ratio and if either design is strong enough to easily support the stress levels its supposed to operate in with a significant safety factor built in.
(H) rods can be built a small bit lighter in weight for any strength level, but the (I) beam rods can generally be built a small bit stronger if weight is not a big concern, but its not the rod design as much as the rod bolts and valve train, lubrication issues and detonation that tends to lead to rod failures
besides from every engineering study I read,rods don,t typically fail due to lack of stiffness under compression, unless they are trying to compress valves or chunks of busted ring land, that came loose due to heat, detonation DAMAGE OR LACK OF LUBRICATION, but MORE COMMONLY under tension when the rod distorts trying to retain the piston thats playing crack the whip trying to stretch the rod.
Stronger bolts, don't flex or stretch as much under high stress....If a bolt stretches, even a small amount bit, it will allow the bearings and the oil clearances to change the bearings supporting film strength a little.

A spun bearing is a result of a lack of proper lubrication of the bearing that has shifted under stress and been destroyed, in most cases due to the lack of correct lubrication or the bolt failing. Under normal conditions, the piston rod, and crank does not touch, they have a thin supporting boundary layer of pressurized oil , that layer of oil between them, cools, cleans and lubricates but only as long as the proper oil flow, pressure and clearances are maintained if something happens to this oil layer, and the bearing is rapidly destroyed, and it is usually referred to as a "spun bearing" but in many cases the rod bolt and bearing failing are proceeded by the piston contacting the valves, once the valve bends a rapid cascade effect results in a piston trying to compress a non- compressible valve into the combustion chamber, the rod and piston, bend or break, and what appears to be a rod failure is actually a valve train component failure, usually proceeded by over revving the engine or a valve train component failure

the typical stock chevy rods weak point is the rod bolts that may stretch or caps, held by the rod bolts, the BETTER ARP rod bolts (L19 )are typically at a minimum 50%-100% stronger,than the stock bolts, if the same diam. is used, going from a 3/8" diam. to a 7/16" diam. adds about a 18% additional cross sectional area, significantly adding to the strength, but its rather silly to refurbish the stock 3/8" bolt BBC rods, in my experiences building BBC engines ,when there are far stronger aftermarket rods already built with ARP cap screw rod bolts and made from 4340 forged steel that cost about the same as all the work typically costs to bush,the small ends, refurbish,the rods,add ARP fasteners, polish, balance those rods and still have an inferior, and weaker rod.

Ive got to ask why anyone would even think seriously of using used stock connecting rods, when you have zero idea as to the cycles they have been thru, in unknown condition with pressed pins that have a core cost of $150-$200
(common cost of a set of 7/16" bbc rods for example)
when NEW ARP 7/16" bolt cap screw 4340 forged rods, are so reasonably priced?
example
http://www.summitracing.com/parts/SCA-26135/

under $300 seems like a much better deal for new rods and 200,000 psi arp rod bolts


http://www.adperformance.com/index.php? ... 2e07cca44d

[grumpyvette]

you might want to keep in mind that its rarely compression, bending rods, its more likely tension forces that cause problems as the piston is yanked away from tdc on the exhaust stroke where theres no compressed air slowing it as it nears tdc, that tends to stretch rod bolts and deform bearings,and that a 600 gram piston, rod assembly effectively weights over 11,000 lbs in a 383 with its 3.75" stroke as it passes TDC on the exhaust stroke


read these links
almost all 1955-1967 Chevy Small Journal connecting rods used 11/32" Connecting Rod bolts, thats .093 sq inches, of shear area vs .1106 for a later larger journal 3/8" connecting rod bolt vs .1505 for an aftermarket 7/16" connecting rod bolt cross section, now stock chevy rod bolts rarely test at more than 160K PSI, better ARP STEEL can run 180Kpsi,-210K psi, thats a huge difference in strength.
, thats 14,880 ft lbs for a 11/32 rod bolt to , up to 31605 ft lbs for the aftermarket bolts
Connecting Rods - Chevy small-block rods have been updated several times, but center-to-center length has remained constant at 5.7 inches, except in the 400-inch engine, which has a special short rod at 5.565" in length with short rod bolts. When the large journal 302 and 350inch engines were introduced in 1967 (with the new large-diameter crank) the rod bolts remained at 11/32-inch diameter. Everything from '68 on up has the 3/8inch bolt rod and the larger diameter journals. It must be remembered that stock rods with 3/8-inch bolts can't be had for the small-diameter crank. This means you can't build an engine with a pre-'67 crank and use a stock rod with the 3/8-inch bolts. Over the years attempts have been made to install the larger bolts in the early rods to produce a small-displacement, high-RPM engine based on the early crank. Due to the availability of later hardware and many problems - and poor results - of installing the big rod bolts, this combination is not recommended,and the aftermarket rods that you can buy from company's like SCAT can easily be DOUBLE the strength or MORE of the stock chevy sb connecting rods
http://arp-bolts.com/pages/technical_failures.shtml

http://www.hotrod.com/techarticles/stee ... index.html

WATCH VIDEO
http://www.youtube.com/watch?v=uTpRfREYa9Q
FastFourierTransportation
posted these links



http://www.deathrev.com/wp-images/2004f ... F_1602.jpg
http://i67.photobucket.com/albums/h305/ ... kb-rod.jpg
http://students.washington.edu/khawki02/rod2.JPG
http://www.deathrev.com/wp-images/rod1.jpg
http://www.twinturbostang.com/97cobra/t ... _Seven.jpg
http://www.zhaust.com/tech/0402/boost/i ... conrod.jpg
http://www.insanedubz.com/Web_images/IMG_bent_rod.JPG
http://www.pattakon.com/tempman/rods.JPG
http://www.ask.com/bar?q=stress+levels+ ... 2Frods.htm
http://www.ask.com/bar?q=stress+levels+ ... index.html
http://www.ask.com/bar?q=stress+levels+ ... engine.htm

http://www.ask.com/bar?q=stress+levels+ ... Length.htm

Even some comparatively high quality forged rods bend:
http://media.merchantcircle.com/2579086 ... medium.gif




lets do a bit of math with a high rpm 383 combo, it might help here

lets take this connecting rod (645 grams)
http://www.summitracing.com/parts/ESP-6000B3D/
this piston (527 grams)
http://www.summitracing.com/parts/UEM-9909HC-060/
and just temporarily ignore the rings,and bearing weight

thats about 18210 grains at 4500 fpm in piston speed thats 75 ft per second
6588 inertial pounds the piston weights at just over 7000rpm, and your looking to reverse its direction of travel , at over 116 times PER SECOND at 7000 rpm, effectively doubling even that load of the stress on the exhaust stroke ,if you don,t think thats absolutely amazing that its potentially possible to do without instantly self destructing you have zero grasp on the potential levels of stress, then we add the fact that theres potentially 600 psi of pressure on the power stroke over a piston or about 7700 pounds resisting the piston on the power stroke but not on the next exhaust stroke and it mind boggling it holds together for even a second or two if we throw in the rings and bearing weights
http://www.summitracing.com/parts/ESP-6000B3D/

If you ever get the idea that selecting high quality connecting rods with ARP 7/16" rod bolts is a waste of cash and effort, consider the results when a rod bolt snaps due to stress at high rpms. you might be able to save the rockers,valve covers and intake manifold and water pump

[grumpyvette]

anything can be broken,under the correct conditions, its finding and removing the potential likely causes, and understanding what their likely too be that's the trick to building a decent engine
strength, obviously it depends on materials, design, care in manufacturing and which connecting rods are being compared properly prepared LS7 or L88 big block rods are a whole lot stronger than the stock 3/8" rod bolts big block rods, but many of the better aftermarket rods are significantly stronger that even the l88 rods
I beam rods typically have a balance pad and thats a good feature, typical H beam rods are SUPPOSED TO BE nearly identical in weight, as they are usually machined not castings (obviously they too occasionally need to be balanced)

btw, if your looking for decent connecting rods at a good price, IVE USED several dozen sets of scat 4340 H beam BIG and SMALL block Chevy rods on some killer, high horsepower, engines and a few sets of eagle and oliver rods also, not one has been a problem, Ive even used a couple sets of CAT brand rods with no problems

http://www.adperformance.com/index.php?main_page=product_info&cPath=67_88_133&products_id=500

http://www.adperformance.com/index.php?main_page=product_info&cPath=67_87_131&products_id=243

http://www.catpep.com/searchengine/sear ... ginetype=4

always get the bolt upgrade

but at these prices it hardly pays to mess with stock rods,
KEEP IN MIND
no connecting rod can survive trying to compress a bent valve or cracked off section of piston,
its hardly a connecting rod flaw if it bends after repeatedly being subjected to the forces required to slam metallic chunks thru a cylinder heads quench area, so if thats what happened replace the bent connecting rods, and carefully inspect the rest of the components and diagnose the root cause of your problem, before just assuming it was a connecting rod failure......if a component failed theres a reason, find it and correct it, in most cases the valve train components were wrong for the application,the valve train components was pushed past its RPM limitations, the geometry or clearances were not correct,were a contributing factor or the lube system, ignition timing, detonation, octane levels,cooling system or operator error was the root cause, rod failures are a SYMPTOM far more frequently than a CAUSE of engine failure

[grumpyvette]

In this article I would like to cover connecting rods. What types are good for what applications, and I’ll touch on rod length, because this is a can of worms I’d rather not open since there are so many things that can change rod length characteristics.



By Andy Jensen


The types of rods are broken into four families: stock, aluminum, 4340 forged and 4340 billet. I know there are some 4130 and 5140 aftermarket rods available, but I have no experience with these.

Stock rods vary from manufacturer to manufacturer, not only in size and shape, but in the amount of power and RPM’s they can withstand. For example, we’ve installed well prepared big block Chevy rods in some 800+HP/7500 RPM nitrous engines with no failures, but a big block Ford rod would never take that and it’s not that I’m pro Chevy, a small block Chrysler rod is a very strong piece. I just call them like I see them.

The preparation we do to a rod depends on the level of power or RPMs it will have to withstand. The minimum, even for a stock rebuild is to shot peen, magniflux and re-size the bearing end. For more demanding use we will side polish the rod. This is to remove any stress risers on the beam area. A stress riser is a surface imperfection that will allow a crack to start. Once the rod is clean and side polished, we magniflux them. If they pass this test we get them shot peened. After peening, the rod is re-sized using SPS bolts. We have had zero rod bolt failures with these and we feel that they are the some of the best available. If a racer supplies a set of good cores, rods prepared in this fashion will cost way less than $200 and hold up pretty well depending on piston weight, RPM, horsepower, and as I stated earlier, the manufacturer.

Now we’ll get into the aftermarket rods. First, we’ll look at aluminum. Aluminum rods are more suited for higher RPM drag racing engines. Some of the advantages are lighter weight and that they absorb some of the shock from the exploding intake charge and from the piston changing direction. They are also more economical than premium billet 4340 rods. The disadvantages are that they are bulky and hard to fit in an engine with a lot of stroke. Another disadvantage is their shorter life expectancy. Most manufacturers recommend changing them after 200 to 400 runs. I’m sure that there is more to the aluminum rod story and if you’re considering a set it’s best to call the people who make them to see if they are right for your application.

Now, on to 4340 forged aftermarket rods. These are a good compromise between cost and reliability. They usually sell for between $600 and $800 and are available from many different manufacturers. The ones we use the most are Oliver and Lunati. They are available in a wide range of lengths and the Oliver rods come in a standard weight and lite weight version.

[Editor's note: The companies mentioned in this article are not an endorsement by Engine Builder. Stay tuned for our 2010 High Performance Buyers Guide for a complete list of con rod manufacturers]

We mostly use forged 4340 rods in engines that are limited oval track and non-nitrous drag applications. For unlimited oval track or high RPM nitrous drag, we use billet 4340 rods. These are the most reliable rods on the market. They are also the most expensive (except titanium rods). They can sell for between $1,000 and $1,200 per set. They are available in a bunch of different lengths and weight ranges. Since they are machined from a solid bar, it gives the manufacturer a lot of freedom to change the size and shape of the rod to suit a given application.

Billet rods are available from many different companies, the ones we use the most are Oliver and Crower. They both seem to be very reliable. We have never had a rod failure when using these rods. This should help in choosing what rods to use in your racing engine. I will shed a little light on selecting the length of your connecting rods, but this is a whole article in itself.

For limited induction engines the rod should be as long as possible. The engines usually don’t make a ton of horsepower so the piston can be pretty short and still hold up. On unlimited induction engines or engines with heads that have a lot of port volume, maximum rod length is not quite as critical so you can leave a little more piston height to get reliability and still not hurt horsepower. This is about as deep into rod length as I’m going to get at this time.

– Tech Tip courtesy of Jensen’s Engine Technologies


how crank stroke effects piston movement and acceleration

viewtopic.php?f=53&t=510

viewtopic.php?f=53&t=247

viewtopic.php?f=53&t=1168

http://victorylibrary.com/mopar/rod-tech-c.htm

http://www.stahlheaders.com/Lit_Rod%20Length.htm

https://www.lunatipower.com/Tech/Rods/RodLength.aspx
By David Reher, Reher-Morrison Racing Engines

“Connecting rods tend to be taken for granted – until they break.”

Imagine riding an elevator that makes a 10-story round trip 7,000 times a minute, alternately stretching and compressing its occupants with every cycle. That’s exactly the kind of punishing treatment a connecting rod endures. A connecting rod must bear the compression force of thousands of pounds of cylinder pressure, withstand the tension loads produced by the piston’s inertia at TDC, and survive the bending loads that try to push the piston through the cylinder wall.

The connecting rods are vital links in every reciprocating engine. They tend to be taken for granted until they break – and when a rod lets go, it will spoil your day and ruin your engine.

In drag racing, the choice of material for connecting rods comes down to steel and aluminum. I’m not privy to the inner workings of Formula 1 racing engines, but we did experiment with titanium connecting rods in our Pro Stock engines a few years ago. While titanium has some appealing attributes, it also has some shortcomings when used as a connecting rod material. The necessity to coat the thrust surfaces, the expense of machining and tooling, and the problems with galling fasteners in titanium convinced me that aluminum was a more practical choice.

Aftermarket steel connecting rods have become popular in mid-level sportsman racing. It’s tough to beat a set of affordable steel rods in a bracket or Super-style racing engine. One of our customers has had a set of relatively inexpensive steel rods in his big-block for 11 years. The engine turns 7600 rpm and makes 1,000 horsepower, so this is not a weak motor. We’ve replaced the bolts during regular rebuilds, but the rods just go back in after every overhaul.

Steel rods have limitations, of course. They’re seldom suitable for a big-inch, go-fast engine. The chief problem is weight. A steel rod for a large displacement motor might weigh 1200 grams, versus 850 grams for a typical big-block bracket engine. Like a valve spring, a connecting rod is subject to its own mass, so a portion of the load on the bolts and cap is produced by the weight of the beam and the small end of the rod. As the rod becomes longer and heavier, the stress on the fasteners and cap increases dramatically.

Heavy steel connecting rods are also tough on pistons. As the crankshaft turns, the rod’s reciprocating motion is controlled by the piston. If it weren’t for the restraint of the piston moving up and down in its cylinder, the rod would sling around in a circle. I often see the telltale evidence of the thrust loads generated by heavy connecting rods on pistons. The pistons are more susceptible to cracks where the pin boss joins the skirt, and the skirts are also more likely to collapse when a heavyweight rod is used.

This brings us to the chief advantage of an aluminum connecting rod: weight. Aluminum weighs approximately 1/3 as much as steel, and because it is so light, connecting rod manufacturers can use thick cross-sections in their rods without incurring a weight penalty. The tensile strength of steel is approximately 200,000 psi; the tensile strength of aluminum is about 95,000 psi. Consequently an aluminum rod can equal the strength of a steel rod at two-thirds of its weight.

Aluminum rods also are a little friendlier to the crankshaft and pistons than steel rods. The aluminum seems to cushion the peak loads, and that becomes apparent in the condition of the bearings and piston pins when an engine is torn down.

The downside of aluminum is its fatigue life. Aluminum loses strength with heat and load cycles, so it has a relatively short lifespan in a highly stressed application such as a connecting rod. Steel, on the other hand, does not fatigue as long as it isn’t stressed to its yield point. Think of a steel paperclip; if the wire is bent back and forth until it reaches its yield point, the wire will break. But as long as the metal isn’t stretched to it’s yielding point, the paperclip will last a lifetime.

Aluminum loses strength when it is subjected to heat cycles. Fortunately in a drag racing engine we have the ability to control engine heat to a great extent. I’ve written previously about the importance of keeping a racing engine’s temperature under control. Now I’ll add the effects of heat cycles on aluminum rods to the list of reasons why it’s advantageous to keep an engine cool.

Aluminum is also highly notch sensitive. A stress riser produced by an exposed bolt thread, a sharp radius or a tool mark is likely to be the point where the rod fails. If a lifter breaks and its needle bearings leave dozens of tiny notches in a set of aluminum rods, it’s an excellent idea to replace the rods. Even though the rods may otherwise be in good condition, the stress risers left by the lifter bearings have compromised the aluminum’s strength. In contrast, steel has relatively little notch sensitivity – although it’s a really bad idea to run a steel connecting rod that’s been cut with a hacksaw just to see how long it will last.

It’s very unlikely that aluminum rods will fail as long as they are replaced at regular intervals. I don’t put new bolts in aluminum rods simply because we install new aluminum rods with every rebuild. If I’m using steel rods in an application where they’re not being stressed to their yield point, then I replace the bolts periodically.

Steel connecting rods are available in two different styles: a conventional “I” beam rod (similar to a factory forged rod) and an “H” beam rod (often referred to as a Carrillo-style rod). I’ve had good success with both styles, so I really don’t have a strong preference for one over the other. In an endurance racing application, the H-beam rod is more suitable for a pressure-oiled piston pin, but that’s not a consideration for a drag racing engine.

Steel connecting rods will provide good longevity at an affordable price in an engine that has a reasonable rod length and doesn’t turn extremely high rpm. As horsepower and engine speed go up, and as the components get bigger, then aluminum rods become a more practical choice.

http://www.hotrod.com/techarticles/stee ... rods_tech/

[grumpyvette]

From the November, 2010 issue of Circle Track
By Jim McFarland





Connecting rod geometry, particularly center-to-center length, can have a material influence on a variety of engine conditions.
It is generally acknowledged that connecting rod geometry, particularly center-to-center length, can have a material influence on a variety of engine conditions. These include specific relationships to valve timing (camshaft design), cylinder pressure history, spark ignition timing requirements and torque output, the latter with respect to the actual shape of torque curves. We'll touch on the more important of these a bit later.

Depending upon specific applications, connecting rods are perhaps some of the most highly stressed parts in an engine, particularly those intended for racing. From the high loads experienced at and just beyond TDC piston position during combustion to the tensile and unsymmetrical loading caused by offset piston pin axis, loads that are actually opposite to combustion pressure loads and stresses set up by lateral inertia, connecting rods become virtual "whips" that mechanically join pistons to the crankshaft.

Further complicating the issue are vibratory loads caused by oscillatory motion of a crankshaft, rotating about its axis while spinning in a normal direction. Visualize this set of load conditions in very slow motion. Each firing impulse intended to accelerate crankshaft rotation is applied as a force delivered in a span of time. Because of its inertia, a crankshaft can't immediately increase its speed and, therefore, is momentarily deflected in the same direction as its rotation. This deflection is local to the crank pin to which the load-delivering connecting rod is attached. Then, because of its elasticity, the crankshaft (at that pin location) will spring back against its direction of rotation, continuing this back-and-forth oscillatory motion until the next firing pulse is delivered to that particular crank pin. The connecting rod is thereby required to absorb what amounts to a series of tensile and compressive loads caused by oscillations of the crank pin, during primary crankshaft rotation.

Keep in mind that we've just provided a very simplistic description of the load dynamics experienced by the connecting rod for only one operational cylinder. The complexity of this varying load environment is increased by orders of magnitude when you add another seven cylinders and turn up the wick on rpm. So, when you think about connecting rods as "shock absorbers," several issues come to mind.

For example, consider cylinder pressure loads not as "hammer blows" to a piston but very rapid pressure rises that are influenced by combustion flame rate and net combustion pressure development. We also know that this pressure "history" is not constant or uniform as it is applied to a piston. Plus, whatever auxiliary forces are applied to a piston are also transferred in some way into the connecting rod. Rods can be designed too stiff, thereby transferring combustion pressure too aggressively to rod bearings and crank journal bearings. They can also be too flexible, and neither condition is acceptable. But in any case, rods need to absorb load spikes and minimize pressure transfer loss to prevent a waste of torque that's ultimately produced by the crank.

Perhaps one area of concern where connecting rod stiffness is important deals with vibratory loads produced by the torsional stiffness of a connecting rod's beam section, as piston weight is reduced. As you might expect, the reduction of rotating and reciprocating mass in an engine's crankshaft assembly can become a trade-off to the absorption of gas and mechanical loads by sheer mass alone. Visualize throwing a medicine ball to a 150-pound person and then to a 250-pounder and you may understand this more clearly.

Of course, to minimize the rotational resistance of a crankshaft assembly, reducing the weight of pistons and rods is a time-honored approach. However, compromising weight for strength and durability is the fulcrum about which this issue pivots. Perhaps one exception to this "rule" was in the early design of composite connecting rods (the so-called "poly motor" of years past), in which first-design rods were inordinately stiff and caused rod bearing failures for a lack of load absorption capability. On the other hand, lightweight materials that offer strength and low mass may be too costly to market, even in the average racing engine. So while other considerations must be included, the fundamental objectives should include strength, low weight, and durability.

In speaking with leading connecting rod manufacturers, you often hear that a high percentage of rod failures don't occur during the high pressure of combustion. Rather, it's during the exhaust stroke that a rod gets "yanked" away from TDC. This sudden movement of the piston causes abnormally high tensile loads in the rod's beam and leads to a fracture in this area, typically somewhere just below the piston pin end.

Also, failures can occur during either valve float or conditions of over-revving the engine. What happens is that the open valves (and lost combustion pressure) don't provide any sort of a cushion for pistons heading toward TDC. So when they pass through TDC, there's nothing to stop them from being "pitched" at the cylinder heads, often leading to another cause of tensile fracture in the beam section. In fact, the "effective" or dynamic weight of a piston passing through TDC under these conditions can be far in excess of its actual static weight. Multiple times, in fact.

Connecting rods become virtual "whips" that mechanically join pistons to the crankshaft and sometimes they fail. But situations like the one pictured above can be avoided by properly selecting and integrating various internal engine components.
Yet another common location for rod failure is a portion sometimes called the "hinge point," which is generally where a connecting rod's beam section changes in cross-section area (wide to narrow). Connecting rod designers frequently work in this area to determine the best compromises between rod strength and material selection. Of course, you should always include proper rod side-clearance, making certain not to provide excessive dimension that allows oil to create over-oiling of cylinder walls. Insufficient side-clearance can lead to over-heated and failed rod bearings, as well.

Finally, if we assume that a piston represents the "floor" of an engine's combustion space, then the rate of piston movement and time spent at each crankshaft angle will affect the rate of change in combustion space (volume). Of the reasons this is important, one is that piston movement can affect mixture density during the compression stroke (and subsequent flame rate and rise of combustion pressure). This, in turn, bears influence on spark ignition timing and the optimization of IMEP (minimizing "negative" torque). During an exhaust cycle, piston motion can also affect efficient cylinder evacuation and, therefore, is linked to proper exhaust valve timing.

Just considering these two peripherals of piston movement, we can immediately see that any changes to a piston's rate of travel may affect net cylinder pressure and power. Connecting rod length can, and does, influence cylinder pressure. Perhaps obscure is the fact that while longer connecting rods produce a larger included angle between rod axis and crank throw (stroke) at the same piston position and crank angle, it is piston motion approaching and leaving TDC and BDC that provides some interesting study.

Here's an example of that. As connecting rod length is increased, piston motion (both acceleration and velocity) away from TDC decreases. This results in a slower rate of pressure drop across the inlet path, therefore causing a reduction in intake flow rate (all else being equal). Unless compensation is made for this change in piston speed, some degree of volumetric efficiency may be lost.

In contrast to this effect upon volumetric efficiency (potential torque), piston "residence time" at and near TDC during combustion tends to hasten flame rate, correspondingly raise cylinder pressure per unit time, and enhance the tendency toward detonation. Reduced initial (or total) ignition spark timing, applied to reduce pre-TDC cylinder pressure, also increases IMEP by the reduction of negative torque. Or it can work against the piston as it approaches TDC during combustion.

Long rod combinations usually like intake manifold passages (actually heads and manifold) that help boost flow rates not provided by more rapidly descending pistons associated with shorter rods. So in addition to adjusting valve timing and lift patterns to match changes in piston speed needed to increase volumetric efficiency for increased rod length, port section areas and even carburetor sizing can be used to help restore reduced flow rates.

There is also the issue with reduced piston side-loading with long rod use. This reduction in friction horsepower has been attributed to power gains, especially when piston speed increases beyond about 2,500 feet/second. Improved ring life with long rods has also been claimed by some engine builders.

So while none of this month's Enginology was intended to advocate the use of short or long connecting rods, it emphasizes the importance of contemplating other engine functions that required consideration when making material changes to the rate of piston travel as a direct function of crankshaft angle. You will find that knowledgeable parts manufacturers, relative to the subject of connecting rod length, generally have a store of information linking how their components can affect an engine's ability to capitalize on rod length changes. If they don't, you may want to consider finding manufacturers who do. The concept of functional parts integration isn't without basis.

[LEJ ZO6]

Some of the newer powder metal rods are showing up in factory engines. Do you have any experience with these ?

[grumpyvette]

powder metal rods by definition are formed from a compressed mix of granulated metallic slurry obviously the exact content of that metallic slurry and how its compressed matter,how it's heated and compressed/forged to form a component,matters a great deal. it can be as strong as a solid forging of top grade steel (4340 etc.) but the metallic mix and the forging process vary a great deal between different connecting rods, if your thinking of using them in a performance application its rarely going to be the best choice for a true performance application,they do make a decent rod for a stock engine but under high stress theres usually better options, they are stronger than the old stock sbc rods or old style (PINK) RODS in the BETTER designs like HOWARDS CAMS SELLS but thats not always true of the O.E.M. powder metal rods the caps are fractured not machined ,making resizing very difficult, as after machining the large end needs extensive reworking.
keep in mind when someone states that a powdered metal rod is (JUST AS STRONG) as a forged rod,you need to consider the thickness of any component, either forged or powdered metal, a more massive component may weigh more but its also likely to be stiffer and stronger, its been my experience that the O.E.M. powdered metal rods are noticeably thinner in cross section, so even if they WERE of similar strength materials.....powdered metal rods are strong enough for the application they are designed for but they do not have the strength of the better aftermarket forged 4340 rods with 7/16" ARP bolts and the cost of those aftermarket rods makes reusing the powdered metal rods in a performance application a bad value

IM OFTEN ASKED WHY I DON,T REBUILD CHEVY CONNECTING RODS, WELL MAYBE A PICTURE WILL HELP,

a good set of SCAT FORGED 4340 forged connecting rods costs less than $400 and they are 150%-200% stronger than MOST OEM chevy SBC rods
it will cost you almost that much to replace the bolts with ARP wave lock bolts, balance and polish and resize stock rods and you have far weaker rods when your done
example

GOOD
http://www.adperformance.com/index.php? ... cts_id=516

BETTER for not much more cash
http://www.adperformance.com/index.php? ... cts_id=241

http://www.mpif.org/designcenter/powder ... ?linkid=43


As in conventional PM, powder forging begins with custom-blended metal powders being fed into a die, then being compacted into a “green” shape, which is then ejected from the die. This compact, called a “preform,” is different from the shape the final part will acquire after being forged. Again as in the conventional PM process, the green compact is sintered (solid-state diffused) at a temperature below the melting point of the base metal in a controlled atmosphere furnace, creating metallurgical bonds between the powder particles and imparting mechanical strength to the preform.

The heated preform is withdrawn from the furnace, coated with a high-temperature lubricant, and transferred to a forging press where it is close-die forged (hot worked). Forging causes plastic flow, thus reshaping the preform to its final configuration and densifying it, reducing its porosity to nearly zero.

Powder forging produces parts that possess mechanical properties equal to wrought materials. Since they’re made using a net-shape technology, PF parts require only minor secondary machining and offer greater dimensional precision and less flash than conventional precision forgings.

Parts fabricated through the PF process are subject to certain limitations. Tooling and the maximum press tonnage capabilities impose size and shape constraints on parts, just as in impression die hot forging. Annual production quantities in excess of 25,000 pieces are typically required to amortize the development costs of tool set-ups and maintenance. Finally, material systems are somewhat limited (all commercial PF products are steel).







read these

http://www.forging.org/FIERF/pdf/FatigueBehavior.pdf

http://www.circletrack.com/enginetech/c ... _4260.html

http://www.superchevy.com/technical/eng ... index.html

Powder-Forged Connecting Rod - The Power Of Powder
Powder Forging Enters The Short-Track World
From the July, 2004 issue of Circle Track
By Larry Jewett
Photography by Courtesy Of Howards Racing Components, GKN Sinter Metals
Powder Forged Connecting Rods Available Connecting Rods
Precision powder-forged connecting...

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Powder Forged Connecting Rods Available Connecting Rods
Precision powder-forged connecting rods have become available for racing applications. Powder-forged components have been used in high-performance applications like Formula 1 racing and have been part of the domestic original equipment automotive products since the mid-'80s.

Technology has proven to be the key to unlock better performance. As methods are tested and found to be beneficial, the supporters line up to take their programs to the next level. Advantage is the universal element sought by all racers.

Sometimes, the advantage can lie deep within the engine. Expensive exotic metals are one way to go about it, but there is a far more cost-effective way to get reliability and performance in some key engine parts.

Howards Racing Components has joined with GKN Sinter Metals to unveil a line of connecting rods for racers. These rods are manufactured in the precision powder-forged process. This allows the rods to be extremely durable for high-horsepower applications. In addition, the cost of the rods is going to be within the range of an average racer's budget.

The name "precision powder-forged connecting rod" has been shortened to "PPF con rod," which is the way it will be referred to from this point forward.
Powder Forged Connecting Rods Con Rod
The design for Howards Racing...

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Powder Forged Connecting Rods Con Rod
The design for Howards Racing Components' PPF Con Rod utilized state-of-the-art computer programs for modern efficiency.

The goals of the PPF con rod were simple. The companies wanted to design a part that was stronger and lighter while keeping cost affordable. The combination of strength and light weight is a definite boost to the production of horsepower.

The technology is new to short-track racers. It has been used for high-performance applications for more than two decades. Auto-motive original equipment manufacturers have also used components using powder metal for nearly 15 years. There's a good chance your street vehicle contains some powdered metal components.

The Process
Just like most operations, the process begins with a need and then a plan to fulfill the need. Once there is an established plan, the part must be designed. In the case of the connecting rod, the designing phase utilized the concept of solid modeling. The solid modeling phase used a CAD (Computer Aided Design) system that insures design integrity. It allows for the accurate prediction of overall weight and center of gravity of the part. Once the manufacturer is satisfied, the file is transferred to FEM (Finite Element Modeling) analysis and used by a CAM system for prototype production.
Powder Forged Connecting Rods Metal Forged
The goals of the powder metal...

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Powder Forged Connecting Rods Metal Forged
The goals of the powder metal forged rod included strength and light weight. The economics became an added bonus.

In the case of this connecting rod, Howards and GKN worked together to determine the best piece. The companies reviewed current billet and conventional forge designs available to the racer. The finished design was machined from billet stock to serve as a proof for the concept. During the analysis of the Finite Element Modeling, the weight was further reduced, and stress areas were identified.

With a definite model in place, the process of determining material composition (a proprietary secret) is underway. A base powder is combined with selected alloying elements, and in some cases, lubrication materials or graphite is added. The newly formed combination is placed into a mixing apparatus for blending the components. This blending process points out one advantage of the powder metal. Custom blends can be accommodated, though GKN has standardized thousands of combinations for components. Physical characteristics can be enhanced with a slight change in the blended material. The process of mixing also allows for closer elemental interaction. Metal-forming alternatives like die-casting molten metals face limitations in alloy choices because of the behavior of the raw material when melted and processed.

After mixing, the material is fed into a compaction machine. The material is placed into a die cavity with two punches. A press squeezes the powder into the shape of the component. The compounds in the existing powder serve as an adhesive to form the part.
Powder-Forged Connecting Rod - The Power Of Powder
Powder Forged Connecting Rods Fracture Split
The fracture-split technology...

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Powder Forged Connecting Rods Fracture Split
The fracture-split technology will provide better alignment for rod bolts.

The next step is sintering. This is the process of forming a cohesive mass by the use of heat without melting the part. During the sin-tering process, parameters such as temperature, atmosphere, belt speed, and environmental factors are monitored and registered. Lubricants and binding agents are driven from the part. The heat of the sintering process forces the alloying agents to diffuse throughout the part. After the sintering operation, parts are maintained in a controlled atmosphere to prevent decarburization. At this stage, the rods are known as pre-forms. The pre-form is quickly heated to above 1,500 degrees, and a mechanical screw press is used for final forging. Force, speed, timing, tool temperature uniformity, and tool lubrication are controlled. The rods are now complete to near net shape and are forged to full density.

The rods also involve a practice known as fracture notching, which falls into the classification of "secondary operation." There are advantages to the fracture split technology that serve the part better than the standard saw cut. Superior alignment is assured with the processing. The fracture split surface will also eliminate fretting, thus there's no need for guide bushings with this procedure.
Powder Forged Connecting Rods Aggressive Testing
GKN's aggressive testing program...

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Powder Forged Connecting Rods Aggressive Testing
GKN's aggressive testing program was a key selling point in its relationship with Howards Racing Components. Static and dynamic testing is used to determine ultimate tensile strength (breaking point) as well as endurance and fatigue.

The parts require other secondary operations. These could include honing, boring, grinding, and drilling. If a chamfered or beveled face is needed for a product, this can also be implemented at this step.

The finished product is thoroughly tested to determine its ability to withstand the demands of the application. After satisfactory completion of the testing phase, mass production of the pieces can be ordered.

Precision powder forging has several advantages over the conventional forging process:

1. Greater material flexibility
2. Fewer burrs that require additional work to remove
3. Minimal weight fluctuation between pieces-allowing easy replacement of a single rod
4. No material textures

In terms of weight fluctuation, the tolerances are tightly maintained. The whole part is weighed and must fall within a total tolerance area. In the case of the connecting rods, by the nature of the part's design, the pin end has a 6 percent tolerance while the crank end has a 2 percent tolerance.
Powder Forged Connecting Rods Rods
The rods are the product of...

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Powder Forged Connecting Rods Rods
The rods are the product of an evolution. They start in the briquette form (left), go through the forging to reach the middle stage, and then become heat-treated and finish-machined before shipment to the customer.

GKN has the capability of making 130,000 rods daily. The material used in the rods is ASTM 4260, which, in many ways, is superior to 4340 steel. The metal standard was established by ASTM International, formerly known as the American Society of Testing and Materials.

The rods will be made in America and can be easily reworked by using oversized bearings available from three different manufacturers. Initially, the rod has become available for the small-block Chevrolet applications. The cost savings was expected to reduce the racers' budget by as much as 40 percent in comparison to units of similar quality. Top quality rod sets, equally matched, are expected to cost $600 at the retail level. The target weight of the small-block Chevy rods is between 500 and 600 grams, and the approximate horsepower range is between 700 and 800.

The search for better technology has found the powder metal application starting at this point, but the drive to find more use is clearly underway. The methodology and materials have been proven in lab tests, product tests, and real life applications. Racers looking for competitive alternatives have to consider the advantages found in powder metal. If they don't, their competition will.

Editor's Note: Special thanks to Al Barra for research and material provided.

Powder-Forged Connecting Rod - The Power Of Powder

In the blending process, the important elements are mixed. GKN has the ability to create custom blends for certain applications.

Sintering is a process that involves heat without melting. As these diagrams and microscopic pictures show, the bonding takes hold as the key components fuse, while the lubricants and binding agents are expelled.
Powder Forged Connecting Rods Blending Process
Powder Forged Connecting Rods Sintering
Powder Forged Connecting Rods Powder Forging
Powder Forged Connecting Rods Taking Shape

An explanation of the complete powder forging process. The first four steps are handled by GKN, while Howards Racing Components will take care of secondary operations as needed.

The powder begins to take shape in the compaction process. The rod will take the briquette form, essentially very brittle, before moving to the sintering cycle.

4340 vs. ASTM 4260 Metallurgy
4340 Round ASTM 4260
* Nickel 1.65-2.00 * Nickel 0.40-0.50
* Molybdenum 0.20-0.30 * Molybdenum 0.55-0.65
* Manganese 0.65-0.85 * Manganese 0.20-0.35
* Chromium 0.70-0.90 * Copper, Max 0.15
* Sulfur, Max 0.025 * Sulfur, Max 0.03
* Silicon 0.15-0.35 * Silicon, Max 0.03
* Phosphorus, Max 0.025 * Phosphorus, Max 0.03
* Carbon 0.38-0.43 * Carbon determined by purchaser
* Iron balance * Oxygen determined by purchaser
* Iron balance


IF your considering rebuilding any first or second generation SBC connecting rods, and especially the powdered steel connecting rods?
honestly why bother, a good forged aftermarket rod with far stronger 7/16" rod bolts, far fewer stress cycles on it, are available for between $270-$360 a set that's rated at 600-1000hp
theres NOTHING you can do to a O.E.M. powder rod that will make it nearly as strong,or will remove the past stress,in a used connecting rod and the last time I priced both adding ARP 2000 rod bolts and resizing and polishing the O.E.M rods and polishing out surface imperfections, the cost for a finished set of those INFERIOR STRENGTH O.E.M. connecting rods would have been similar or HIGHER.
rods normally fail in TENSION, when the rod bolt stretches distorting the big end an pinching bearings or allowing the piston to contact the heads theres no way that a O.E.M. 3/8" rod bolt can match the strength of a 7/16" ARP rod bolt
theres at least a 100% -150% higher margin in the larger diam. ARP bolts and 4340 forged rods

[grumpyvette]

Back to Basics: Reconditioning Connecting Rods


When you're looking at connecting rods and considering returning them to service, there are many things you must consider.

By Brendan Baker

Brendan Baker

When you're looking at connecting rods and considering returning them to service, there are many things you must consider. They are one of the most critical pieces of the engine puzzle and under great strain when in operation, so you must pay attention to the details during the rebuilding process.

There are many times when reconditioning the connecting rods is a necessary part of engine rebuilding. In many applications it is acceptable, and significantly less expensive, to rebuild rather than replace a set of rods. In the heavy-duty market, for instance, many engine rebuilders prefer to recondition the connecting rods whenever possible because the components are typically expensive to replace and it's not always necessary. However, like the rest of the engine, there are "best" practices that must be followed to ensure a quality engine build and to avoid costly comebacks.

Experts say reconditioning connecting rods involves thoroughly cleaning them first to check for any visible damage. After cleaning and inspecting them, you may find obvious clues that damage exists. Knicks and burrs, or discolored rods can often be signs of a rod that will fail down the road.

The next step is to put the connecting rods through a magnetic particle inspection (MPI). This step will reveal any hidden damage such as cracks or other stressors and imperfections that cannot be seen. After the MPI has been performed, if the rods still look to be in good shape, they should be checked for bend and twist, which if too much, may negate the rest of the reconditioning process. Experts say too much bend or twist may have been the result of an over-revved engine or insufficient oil clearance, and if not properly straightened or replaced, will lead to certain engine failure.

Careful inspection and handling isn't reserved only for used rods, however. One engine builder cautions that you should always check the connecting rods thoroughly even when they're new, because you never know when one will be out of spec and create problems down the road. And new or used, that's the last thing you want to have happen to your rebuilt or remanufactured engine.

The main purpose of reconditioning rods is to build a set of rods that are straight and of the correct length. In typical light-duty applications, four- and six-cylinder gasoline and diesel engines, experts say the rods should be machined back to original specs with no more than .0025" of bend and .00425" of twist. A rod with too much bend will limit oil clearance from one side to the other and possibly lock up at the pin end or at the thrust face on the crankshaft. Furthermore, they must have round and concentric bores, and the fasteners must also be able to withstand the stresses of that application - whether it's a performance engine or heavy-duty application.

To ensure long engine life, the rods must be aligned correctly and the bearing surfaces must be smooth and perfectly round. Any lobing, chatter or misalignment, particularly in engines that operate at higher revs, will affect the engine's performance.

After the rod has been cleaned and inspected thoroughly, it should be put back together with the rod bolts torqued. With a stretch gauge, check each rod bolt for proper stretch. If the stretch is out of specification, then replace the bolt. While some engine builders say that it is safer and less expensive to just replace the rod bolts instead of measuring the stretch, others say that practice really depends on the application, because some high performance rod bolts can be quite expensive.

After the caps are torqued on with acceptable rod bolts, measure the big end bores. This will help you to determine how much to take off the caps and what size you'll need to hone them to. In general, you want to take off as little material as possible to make the bore round again. Experts say you should not take off more than .002" of material off the big-end at a time. After you hone the big end, measure the rod to see what size bushing you need to put in the pin end.

If during the inspection process a bent or twisted rod is found, it may be possible to straighten. One method of correcting bend or twist is called cold bending. This can be achieved using a special holding fixture. When performing this procedure, it is important not to nick or scratch the rod, caution experts. Nicks and scratches weaken the connecting rod and may lead to possible breakage.

Experts say you must first determine the direction of bend or twist. Most bends in the rod will be located near the small-end bore. Place the connecting rod into the straightening fixture using the correct size big-end and small-end adapters. Install the cap and torque the cap bolts to specifications. Select the appropriate bending bar. It should closely fit the rod to prevent nicks and scratches. Use the bar to bend the rod in small increments. Measure the progress on a rod alignment fixture.

Once the connecting rods are straightened, bored and honed, then you can put the proper size bushing in the small end, which is a very important step according to some engine builders. It is recommended that you press out the old piston-pin bushing and install new ones. And to ensure that the bushing won't rotate, you should expand it to conform to the small end bore. To expand this bushing, press a hardened steel ball through the I.D. of the new bushing. This will lock in the new bushing and prevent it from spinning in the bore. If you heat the rod to install the new bushing, you should allow it to cool before you expand the bushing with this broaching technique. Then grind the cap to the correct center-to-center dimension and hone the big end and install new rod bolts.

There are many different types of connecting rods from cast steel to powder metal (PM) "cracked" rods to all the various types of performance rods.

More than half of the connecting rods used in today's late model engines are powder metal I-beam design. PM rods are constructed by compressing powdered steel into a mold and heating it to a high enough temperature where the powder melts and fuses into a solid piece. This process allows the rods to be cast with very precise tolerances, thus reducing the amount machining required to finish the part, making it less expensive to produce higher quality rods.

PM rods are made up of a composite of alloys that allow rod caps to be "cracked" at the parting line rather than split with a straight cut. Many PM rods are not serviceable because you cannot grind down the caps to bring it back to original specifications. In some cases, there are oversize O.D. bearings available that will allow you to hone the big-end and fit a larger bearing.

The benefit to manufacturers is that the fractured PM rod is popped out like an egg with very little machining to make the center-to-center distances right. It comes out of the casting process the final size and is broken at a scored line that is part of the design. PM rods can be manufactured for less cost than traditional rods and is a more durable component, experts note.

The resulting fracture is like a piece of broken china. It has a very distinctive surface that custom fits together. The fracture has more surface area because you have peaks and valleys, and the alignment is more accurate since the cap only fits together one way.

For engine builders, there's not much you can do with fractured PM rods. You can't cut the caps because of the unique break on each one. And, for the most part, you cannot hone the bore because there are very few oversize O.D. bearings available. Some suppliers carry oversize O.D. bearings for the big end of popular applications, but we're uncertain if bushings are available for the pin end.

For performance applications, some engine builders check the Rockwell hardness level of the rods before continuing with a rebuild. Performance rod manufacturers know what heat treatments have been applied and what hardness range is acceptable. Before reconditioning a performance rod it may be a good idea to contact the rod manufacturer. One manufacturer of performance rods says that any rod over 43 Rockwell C, isn't worth rebuilding. If the hardness level has dropped, it's a good indication that the rods were overheated and it has affected the heat treatment. Experts also caution that the color of the rods may be misleading, if the problem is caught soon enough and it hasn't affected the heat treatment then they'll probably be acceptable to recondition.

After rods pass the hardness test and are cleaned and inspected, the caps should be bolted back on and then torqued to specification. Using a stretch gauge, check each rod bolt for proper stretch according to manufacturer specifications. Some experts say you that you should replace all rod bolts as a matter of practice but others say it depends on the application because performance rod bolts can be expensive.

It is recommended that if the rod requires straightening to replace the rod bolts after the straightening process. Most connecting rod bolts are press-fit into the connecting rod, so it's a good practice to press both bolts out at the same time instead of hammering them out one at a time. They should press out easily. If excessive pressure is required, you may have to heat them in a rod heater, otherwise you could break or bend the rod.

After the caps and rods are machined, new bolts can be installed. When installing the bolts, it is important to protect the parting surface of the rod. A fixture can be made or purchased for installing the bolts. With the rod located over the fixture, the bolts can be seated with a punch or hammer.

Reconditioning connecting rods is an important and often times a necessary step in the engine rebuilding process. They are under tremendous stress from continuously stopping and changing direction, combined with the weight of the piston and speed of the engine beating on the bearings and pulling on the rod bolts that hold everything together. The processes used to recondition connecting rods vary a little from engine to engine but the end result should be the same - straight rods and smooth, round bores.

[grumpyvette]

Connecting Rod Reconditioning: More to it than you might think


The processes used to recondition connecting rods may vary a little from one rebuilder to the next, but the end goal is always the same - straight rods with round bores

By Brendan Baker

Brendan Baker

The connecting rod plays a vital role in the engine. But a connecting rod is under tremendous stress, with the weight of the piston sitting on top, changing direction thousands of times per minute. This continuous stopping and changing of direction combined with the weight of the piston and speed of the engine hammer on the bearings and torture the rod bolts which hold everything together.

Proper geometrical alignment and bearing surfaces that are smooth and perfectly round is the best way to ensure long engine life and happy customers. Any unwanted lobing, chatter or misalignment, particularly in engines that operate at high rpms, will affect the engine's efficiency.

One of the most important aspects of rebuilding an engine is to recondition the connecting rods. There are many different types of connecting rods from cast steel to powdered metal "cracked" rods to all the various types of performance rods. The processes used to recondition this engine component may vary a little from one rebuilder to the next, but the end goal is always the same - straight rods with round bores. Sounds simple, but like anything worth doing, there's always more to it than you think.

Typically, reconditioning rods involves cleaning them thoroughly, then checking them with magnetic particle inspection for any cracks. Then the rods are checked for straightness because any bend or twist in the rod may result in oil clearance problems and likely lead to a failure.

A visual inspection of the rods will also include looking for any signs of overheating, which may be indicated by a "bluish" appearance. If the rod has been overheated, its structural integrity may have been compromised, according to the rebuilders we interviewed for this article.

"If a guy has overrevved his engine, we go through and magnaflux all the parts," says Kenny Burns, Harry's Machine Works, Dodge City, KS. "Connecting rod material is typically pretty good, but sometimes the machine quality leaves something to be desired. Therefore, we check everything, even brand new rods."

On the performance side, some rebuilders will check the hardness before declaring them fit for the junk pile. "You can test the heat treatment with a Rockwell tester," says Roger Friedman, Dyer's Top Rods. "We know what our rods should be. They're usually in the 42-43 range on the Rockwell C scale. If a rod got hot enough to change that, it's junk to us."

Friedman cautions that color isn't always a true indicator, however. "We'll sometimes see some rods that were affected when an oil pump belt came off, for example. If you catch them soon enough, they will still turn color, but if the rods test okay, we will shot peen them, re-cut and resize them and reuse them."

After the rod has been cleaned and inspected thoroughly, it should be put back together with the rod bolts torqued. With a stretch gauge, check each rod bolt for proper stretch. If the stretch is out of spec, then replace the bolt. While some engine builders say that it is safer and less expensive to just replace the rod bolts instead of measuring the stretch, others say that practice really depends on the application, because some high performance rod bolts can be quite expensive.

After the caps are torqued on with acceptable rod bolts, measure the big end bores. This will help you to determine how much to take off the caps and to what size you'll need to hone them. In general, you want to take off as little material as possible to make the bore round again. After you hone the big end, measure the rod to see what size bushing you need to put in the pin end.

"The ultimate goal when reconditioning rods, is to come up with a set of rods that are straight and of the correct length," says Jay "Dr. Diesel" Foley, of Foley Engines, Worcester, MA. "In common four- and six-cylinder gasoline and diesel engines, the rods must be machined back to original specs with no more than .0025" of bend and no more than .00425" of twist. A rod with too much bend will limit oil clearance from one side to the other and possibly lock up the engine at the pin end or at the thrust on the crankshaft. In addition, they must have round and concentric bores, and the fasteners must also be able to withstand the stresses of a modern engine."

Once the connecting rods are bored and honed, then you can put the proper size bushing in the small end, which itself is a very important step. "We are very concerned about the piston-pin bushing relationship," says Foley. "We always press out the old piston-pin bushing and install new ones. But that is only half the battle. To ensure that the bushing won't rotate, we expand it to conform to the small end bore. To expand this bushing we press a hardened steel ball through the ID of the new bushing. This will lock in the new bushing and prevent it from spinning in the bore. If you heat the rod to install the new bushing, you should allow it to cool before you expand the bushing with this broaching technique. Then grind the cap to the correct center-to-center dimension and hone the big end and install new rod bolts."

According to Harry's Machine Works' Burns, keeping the rod straight is very important. However, one of the difficulties his shop faces is finding aftermarket wrist pins that are the correct size. "Some aftermarket suppliers are making wrist pins that are supposed to be the same size as OE but they are not," he explains. "We have had a hard time trying to get the right sizes. Sometimes the pins are .001? to .003? off the OE specs. Within that application we have seen differences of up to .003? and we're trying to keep the tolerance within .0002" to .0003"."

Burns says that his shop uses a similar process to Foley's for reconditioning connecting rods. Both Foley Engines and Harry's Machine primarily rebuild diesel engines. Rebuilding diesel rods isn't much different than gas engine rods, except they're much bigger and the center-to-center distance is has to be exact. Since diesel engines operate on a compression cycle, rod lengths have to be correct. "We can shorten them or lengthen them," Burns says about diesel rods, "it just depends on how much has been taken off the block. So the center-to-center distances are critical."

Fractured Rods
Fractured rods are a fairly new phenomena. Ford was one of the first on the automotive side to use a fractured rod in the 4.0L engine, which was one of its first new generation engines in 1990. The fracture method has proven to be less expensive for manufacturers and it produces better quality because it is forged in one piece and then 'cracked' at the rod cap.

"Before fractured rods were invented, conventional rods were two components," says Dave Hagen of the Engine Rebuilders Association (AERA). "You would have one piece, which was the cap and another that was the beam. The two pieces were close enough to bolt together; then you would have to do several machining operations to get the center-to-center distances correct. The fractured rod, on the other hand, is a powdered metal rod that allows the manufacturer to pop it out like an egg with very little machining to make the size exactly right. It comes out essentially the final size and then is broken at a scored line that is part of the design. Once it's broken or 'cracked,' it's done. It can be manufactured for far less cost than a traditional rod and it's a more durable component."

According to Hagen, the inside diameter of a fractured rod bore is scored and then some pressure is applied until it snaps. The resulting split is like a piece of china that has been broken. It has a very distinctive surface that custom fits together. The fracture has more surface area because you have peaks and valleys, and the alignment is more accurate since the cap only fits together one way.

For rebuilders, there's not much you can do with fractured rods. You can't cut the caps because of the unique break on each one. And for the most part, you cannot hone the bore because there are very few oversize OD bearings available for them. Hagen says that some suppliers carry oversize OD bearings for the big end of the more popular models, like the modular 4.0L and 4.6L Fords, but it's uncertain if there are any bushings available for the pin end. So there's a little bit of rebuildability with fractured rods but not much.

Now, some heavy-duty manufacturers are going to fractured rods. "There are some heavy-duty manufacturers making them, like John Deere is coming out with some now, but with fractured rods we can't do much with them," acknowledges Harry's Machine Works' Burns. "We measure them to check the size, and that's about all we can do until there are oversize OD bearings available."

New Methods
For years, connecting rods have been honed on specialized rod honing machines, which are available from many leading manufacturers. These machines have been the standard, produce excellent results and are still widely used throughout the industry. However, Sunnen and Rottler have both recently come out with new systems that take a totally different approach to rod reconditioning.

Sunnen's system is called the KGM-1000 Krossgrinding System®. The KGM system utilizes an easy-to-use computer control, diamond tooling and a feed system that gives the operator high accuracy and speed in the production of precision reconditioned connecting rods. The company says the system is extremely accurate for honing connecting rods, and is capable of holding very tight tolerances, achieving accuracies of .00001" in straightness and .00015" in roundness.

Rottler has also designed a completely new system that works with the F-65 and F-67A multi-purpose machines. According to Rottler's Anthony Usher, the company wanted a system that could bore both the big end and the small end in one setup.

"When we decided to get into the rod reconditioning business," Usher says, "one of the big problems we saw was that rods bend and twist. When you have two setups you can sometimes create other problems. We decided to design a system where a rebuilder could lay the connecting rod horizontally and set it up so both the big end and the small end could be open. With both ends open you can machine both ends in one machine and in one set up and achieve perfect parallelism between the centerlines of both ends."

Rex Crumpton Jr., of Memorial Machine in Oklahoma City, OK, says his shop has both a Berco rod honing machine and a new Rottler system. According to Crumpton, both systems work excellent and he can achieve good results either way. Memorial uses the Berco machine for doing smaller stuff and the Rottler for reconditioning larger rods.

"Honing is excellent, there's nothing wrong with doing rods that way," says Crumpton. "But boring can be a bit more precise. You don't have to worry as much about stones loading up, which could produce taper. As long as you have a good operator who is paying attention, both methods work fine."

[grumpyvette]

Choosing The Right Connecting Rods
All About Connecting Rods: WhatÂ’s Right For You?
From the February, 2009 issue of Hot Rod
By Steve Magnante
Photography by Steve Magnante
Share





KEEP IN MIND
no connecting rod can survive trying to compress a bent valve or cracked off section of piston,
its hardly a connecting rod flaw if it bends after repeatedly being subjected to the forces required to slam metallic chunks thru a cylinder heads quench area, so if thats what happened replace the bent connecting rods, and carefully inspect the rest of the components and diagnose the root cause of your problem, before just assuming it was a connecting rod failure......if a component failed theres a reason, find it and correct it, in most cases the valve train components were wrong for the application,the valve train components was pushed past its RPM limitations, the geometry or clearances were not correct,were a contributing factor or the lube system, ignition timing, detonation, octane levels,cooling system or operator error was the root cause, rod failures are a SYMPTOM far more frequently than a CAUSE of engine failure
viewtopic.php?f=52&t=181

viewtopic.php?f=54&t=2187




Cast Steel

Stock Forged Steel

Aftermarket Forged Steel








Fully Machined Forged Steel

True Billet Steel

Aluminum

Titanium

One of the most important decisions youÂ’ll make when building your next engine is what rods to use. Whether itÂ’s a slightly warmed-over stock rebuild or an all-out strip-stormer, any time you increase output, the first thing thatÂ’s tested is the strength of the connecting rods. Ignoring weight issues, most connecting rod upgrades do not add significantly to power output. What they do is far more important: They allow the ported heads, hotter cam, extra carburetion and other hop-up tactics to complete their mission. LetÂ’s take a look at the battle zone tucked away in your crankcase.

As a piston reciprocates between top dead center (TDC) and bottom dead center (BDC), the rod itÂ’s attached to experiences power loads and inertia loads. Power loads result from the expansion of burning gases during combustion that push down on the head of the piston and cause the crank to turn. Thus, power loads are always compressive in nature. This compressive force is equal to the area of the bore multiplied by the chamber pressure. A cylinder with a bore area of 10 square-inches (3.569-bore diameter) with 800 psi of pressure is subjected to a compressive load of 8,000 pounds. ThatÂ’s 4 tons that the connecting rod must transmit from the piston to the crankpin, and do it hundreds of times per second at racing speeds.

Inertia loads are both compressive (crush) and tensile (stretch). To better understand them, let’s pull the heads off the engine and forget about the combustion process for a moment. When the rod is pulling the piston down the bore from TDC, the mass of the piston plus any friction caused by ring and skirt drag imparts a tensile load on the rod. Once the piston reaches BDC, the dynamics shift. Suddenly the rod is pushing the mass of the piston as well as the friction load back up the cylinder bore, and a compressive load on the rod results. Then the piston stops and reverses direction to head back down the bore, so the inertia of the piston, once again, tries to pull the rod apart as it changes direction. The size of the load is proportional to the rpm of the engine squared. So if crankshaft speed increases by a factor of three, the inertia load is nine times as great. At 7,000 rpm, a typical production V-8 with standard-weight (read “heavy”) reciprocating parts can generate inertia loads in excess of 2 tons, alternately trying to crash and stretch the poor rods.

OK, now weÂ’ll reinstall the heads, turn the fuel pump and ignition system back on, and restore valve operation. The principles of inertia loading are the same, but conditions become even more severe now that the plugs are firing. Even more tensile loading on the rod comes from the work required to suck air and fuel through the intake tract and into the combustion chamber during the intake stroke. Once the piston reaches BDC, both valves close and the rod must push the piston back up to TDC on the compression stroke. But near the end of the trip toward TDC, the spark plug fires and the compressed fuel mixture begins to expand with opposing force before the piston reaches TDC. This causes a sudden surge of compressive energy that must be resisted until the orientation of the crankpin makes it mechanically possible for the piston and rod to change direction and be pushed back down to BDC during the power stroke. Remember, the size of the loads is proportional to the rpm of the engine squared. But thatÂ’s not all.

By far, the greatest test of a rodÂ’s integrity is experienced near the end of the exhaust stroke when the cam is in its overlap phase. In overlap, both valves are open as the piston pushes the last remnants of spent combustion gas out the exhaust port. The intake valve is held open so that fresh intake charge is available the very instant the piston begins generating suction on the downward intake stroke. What makes the overlap period so hazardous is the fact that there is no opposing force applied to the head of the piston (in the form of compressed gas) to cushion the change in direction. This is the load that stretches the rod, ovals the big end, and yanks hardest on the fasteners. If you donÂ’t want your engine to scatter, youÂ’ve got to make sure the connecting rods are always one step ahead of any performance upgrades. But which ones are right for you? Read on for a complete rundown.

Cast-Steel

We won’t waste much time discussing cast-steel rods because they’re poorly suited to any type of serious performance use. Though the casting process is very inexpensive and results in “near net” shapes that require minimal machining, the lack of a cohesive grain pattern and compromised molecular binding yields brittle parts. Trust us, brittle connecting rods are the last thing you want in a performance engine.

In the ’60s and ’70s, American Motors, Cadillac, Buick, and Pontiac all used cast rods in a wide variety of engine designs. In an effort to improve molecular binding and strength, the molten metal was injected into the mold cavity under high pressure. The resulting castings may have been good enough for use in everything from GTOs to Jeeps, but they have no place in anything other than the most fanatical numbers-matching restoration effort. Worst of all, these cast parts had to be made heavier than comparable forged rods to maintain strength. When you consider that a cast “Arma-Steel” Pontiac 455 rod weighs 31.7 ounces and a stock Chevy 454 forged rod weighs 27.4 ounces, you’ll agree they’re the automotive equivalent of recycled cardboard.

Stock Forged Steel

Original-equipment forged steel rods are the next step up the strength and reliability ladder. Detroit-sourced OE-forged rods begin life as bars of carbon steel that are passed through a rolling die. The rolling process compacts the molecular structure and establishes a uniform, longitudinal grain flow. The bars are then heated to a plasticized state, inserted into a female die, and pressed into the near-final shape while a punch locates and knocks out the big end bore. In doing this, the grain flow at the big end is redirected in a circular pattern, like wood fibers surrounding a knot, and excellent compressive/tensile strength results. Finally the rod is put through a trimmer (that leaves the characteristic thick parting line on the beam), the big end is severed and machined to create the cap, bolt surfaces are spot-faced, then final machining and sizing take place.

But there are some drawbacks. When the forging hammer hits the hot bar, heat transfers from the bar to the hammer causing a phenomenon called de-carb (decarburization). Here, trace amounts of the carbon in the steel migrate to the surface resulting in a rough finish full of what metalurgists call “inclusions.” An inclusion is described as anything that interrupts the surface of the metal, or a lack of cleanliness (impurities) in the material. The effect of a surface inclusion can be likened to a nick in a coat hanger. Bend it enough times and the wire will fail, usually right at the nick. The rough surface caused by de-carb affects the surface to a depth of 0.005 to 0.030 inch and is packed with inclusions that are a breeding ground for cracks. The old hot rodder’s trick of grinding and polishing the beams is a valid solution to this problem, though far too labor-intensive to ever be considered by Detroit.

When it comes to inclusions caused by impurities, DetroitÂ’s need to control costs can result in purchases of bulk steel that may (or may not) contain contaminants such as silicon that are not detected during manufacture. Such impurities can interrupt the grain boundaries between the parent molecules and lead to a fracture minutes or years after the rod is first installed in an engine. ItÂ’s a matter of luck and what kind of abuse the flawed rod is subjected to.

With very few exceptions, the weakest link in a stock forged rod is the fastener system. The rod bolt is usually the most marginal component. Simply upgrading from stock bolts to quality aftermarket replacements can improve durability by 50 percent. Just be sure to have the big end re-sized to restore concentricity any time the bolts are removed. Stock forged steel rods are an economical choice that should be able to handle one horsepower per cubic inch with quality fasteners, and as much as twice the factory-rated output if the beams are polished.

Aftermarket Forged Steel

Attention to detail and better parent material are the main attractions offered by aftermarket forged steel rods. Though the forging process is much the same, aftermarket rods are typically made from high- carbon SAE steel such as 4340, 4140, and 4330 that is far superior to the low-carbon 51-series steel used in most OE-forged rods. The SAE certification system quantifies the purity of the metal via microscopic examination that computes phosphorous and sulphur content, individual grain size, and other key indicators. By using SAE-certified material, makers (and users) of aftermarket forged rods can rest assured that hidden impurities are not lurking deep within the molecules to compromise strength.

Most aftermarket forged rods benefit from extra care during the critical machining operations. This alone can make or break a connecting rodÂ… literally. The assumption that careful hands have assured closer tolerances and accuracy in the finished product is a valid one. Usually no heavier than stock rods, aftermarket forged rods already come equipped with premium fasteners and should be included in any street and strip engine assembly that will run in excess of 6,500 rpm with stock stroke or 5,500 rpm with increased stroke. The prices keep tumbling, and more applications are available now than ever. ThereÂ’s no excuse not to step up.

True Billet Steel

True billet steel rods are fairly uncommon in todayÂ’s marketplace. Manufacturing begins when rough shapes are flame-cut from a plate of premium quality forged high-carbon steel (usually SAE 4340), then finish-machined to the required final specifications. Similar to cutting a pattern from a sheet of cloth, manufacturers benefit from true billet rods because they do away with the need to make expensive forging dies. These dies can cost between $35,000 and $45,000 a pair, and several may be needed to supply the wide range of shapes and sizes needed to fit all the various applications in the hot rodding galaxy. On the contrary, the dimensions and physical characteristics of a true billet rod are only limited by the size of the plate it will be cut from.

Although the rolling process that creates the plate of parent material gives a uniform, longitudinal grain flow with excellent molecular bonding properties for outstanding strength, there is one minor shortcoming. True billet rods lack the circular grain flow inherent to the big end of forged steel rods. Instead, the longitudinal grain flow continues undisturbed throughout the shoulder and cap sections. This does compromise some strength, but industry experts say it is a minor issue and is responsible for, at worst, a 15-percent reduction in the ultimate hoop strength of the bearing hole.

On the positive side, true billet rods are inherently free from the surface degradations caused by the forging process. A fully machined billet rod has virgin, high-quality material of uniform composition all the way from the core to the external surface. This makes it more resistant to the formation of cracks, a detail that more than makes up for the stubborn grain flow at the big end.

Fully Machined Forged Steel

Commonly misidentified as “billet” rods, fully machined forged steel rods are exactly what the name implies. Quite simply, they’re premium-grade forged rods that are treated to a high-tech shower and shave. The machining process eliminates undesirable surface imperfections and allows improvement of the shape for increased strength and/or reduced mass.

Before the advent of readily available CNC-machining equipment during the last 15 years, the material removal had to be performed on manual machines at great expense. Combined with the cost of the needed forging dies, the primary exclusive benefit of forged rods (dedicated big end grain flow) was not deemed to be worth the added expense, so most high-end manufacturers stuck with true billet rods. But with the manufacturing cost reduction made possible by automated CNC workstations, the economics shifted and it has become possible to couple the advantages of a forging with a pristine machined billet-like surface in the same rod. It truly is the best of both worlds, and for this reason, fully machined forged steel rods are the ultimate choice for strength where weight savings of the reciprocating assembly is not a primary goal. TheyÂ’re a great choice for any high-performance application short of Top Fuel.

Aluminum

Aluminum rods are manufactured by the forging process, or they can be cut from a sheet of aluminum plate, billet-style. Aluminum rods are generally 25- percent lighter than steel rods, and for this reason theyÂ’re very popular with racers looking to shed mass from the reciprocating assembly. Lighter reciprocating parts demand less energy to set into motion, allowing more of the force of combustion to be applied to the wheels. Lower reciprocating mass also allows the engine to gain crank speed faster for quicker rpm rise after each upshift, to keep the engine near the peak of the power curve. ThatÂ’s the good news.

The downside is that aluminum has a much shorter fatigue life than steel, perhaps one-tenth as long in a racing environment. This means youÂ’ll have to measure for stretch and replace suspect rods at regular intervals to stay ahead of possible catastrophic failure. How long will they go? That depends on how hard theyÂ’re loaded and if theyÂ’re abused. WeÂ’ve all heard stories about hot rodders getting 100,000 street miles out of a set of aluminum rods. Could be. But the fact remains that aluminum has a tendency to work-harden with use. Going back to the analogy of the coat hanger, if you keep twisting it, itÂ’ll break. ThatÂ’s work hardening, and an aluminum coat hanger canÂ’t handle the same strain for nearly as long as a hypothetical steel coat hanger.

Another hassle is the fact that aluminum rods must be made physically larger because the ultimate tensile strength is about half that of a good steel rod. The added bulk often causes clearance problems inside the crankcase, especially when theyÂ’re swinging from a stroker crank. Some aluminum rod users abuse them without even knowing it. A cold motor must be warmed thoroughly because the expansion rate of aluminum is twice that of steel. The difference in expansion between the steel crankpin and aluminum big end can restrict the oil film clearance until the temperature of all parts stabilizes. Wing the throttle on an ice-cold motor, and you might be looking at spun rod bearings, or worse.

Aluminum rods can handle plenty of horsepower. YouÂ’ll want to check with the manufacturer for specifics, but it is safe to say that 2 horsepower per cubic inch is just the beginning. WeÂ’ll err on the side of caution and say that aluminum rods are best suited to race-only engines where regular inspection can ward off potential trouble.

Titanium

Got a huge wad of cash burning a hole in your wallet? Then you’ll want to know that titanium rods offer the highest strength-to-mass ratio of them all. A well-designed titanium rod is about 20 percent lighter than a comparable steel rod. Titanium is the most abundant element in the earth’s crust, but it must be alloyed with other metals before it has the properties needed for the manufacture of connecting rods. The most common alloy is called “Titanium 6-4” because it has 6 percent aluminum and 4 percent vanadium to improve machineability.

Like steel and aluminum rods, titanium rods can be forged or cut from a billet. Given a choice, titanium rods are most durable when manufactured by the forging process. This is because the grain size of even the best aerospace grade titanium is less than steel. In a Richter-esque grain-sizing scale where a 6 rating is twice as tight as a 5 rating, titanium rates between 5 and 6 while high-carbon steel is far more cohesive, rating as high as a 9. To offset the possible negative impact on strength, a fully machined forged titanium rod is the best type thanks to the improved grain structure around the big end versus a cut-out true billet titanium rod.

Though raw titanium costs five times as much as raw carbon steel, the average retail cost of a set of titanium rods is “only” about twice that of steel. The increased consumer cost reflects the fact that titanium becomes “gummy” when machined and requires specialized tooling and slower feed rates. Titanium expands at about the same rate as steel and is resistant to work hardening, so you could run ’em in your street car with no problems as long as your wife never sees the credit card bill. So where do titanium rods really shine? In any all-out racing effort where an approximate 15-percent reduction in ultimate tensile strength is an acceptable trade-off for an approximate 20-percent reduction in connecting rod weight. As for ultimate power capacity, know that they’re used in everything from 9,000-rpm NASCAR motors to a handful of 6,000hp Top Fuel motors (though most teams use aluminum). With the right communication between you and the manufacturer, they’ll handle anything you can throw at ’em. Just be sure not to scratch them! Titanium is very “notch sensitive.” Small surface imperfections caused by rough handling must be polished immediately, or they can grow quickly.

[DorianL]

Fantastic thread!

[grumpyvette]

I,m glad someone reads this stuff!

http://www.scatcrankshafts.com/
good quality


http://www.catpep.com/catalog/2008CATALOG.pdf
not quite as good but still acceptable

http://www.eaglerod.com/mosmodule/bolt_torque.html

http://www.eaglerod.com/
even lower quality , Id pass.

MEASURING CONNECTING ROD BOLT STRETCH
by Mike Mavrigian
http://www.precisionenginetech.com/tech ... ch-part-1/

Tightening connecting rod bolts while measuring bolt stretch provides a much more accurate method of achieving proper bolt preload and clamping force.

Professional performance and race engine builders have long realized that the correct approach to tightening connecting rod bolts is to stress the bolts into their “working” range of elasticity, but not beyond. Since OEM connecting rod bolts may vary in terms of their ideal torque by as much as 10 lbs./ft. from batch to batch due to variations in heat treating and materials, if the concern is to arrive at both peak bolt strength as well as maintain concentricity of the rod big-end, the rod bolts should be measured for stretch instead of simply tightening until the torque wrench hits its mark.

In simple terms, in order to measure bolt stretch, first measure the total rod bolt length (from the head surface to the tip of the shank) in the bolt’s relaxed state. Then monitor bolt length as you continue to tighten until the specified amount of bolt stretch has been achieved.

The difference in length indicates the amount of stretch the bolt experiences in its installed state. For the majority of production rod bolts, stretch will likely be in the 0.005″ to 0.006″ range (this is a generalization; always follow the specific stretch specified by the bolt maker). If it’s difficult to achieve enough stretch, the bolt is probably experiencing too much friction that is preventing the proper stretch (requiring lubricant on the threads). If stretch is excessive, the bolt may have been pulled beyond its yield point and is no longer serviceable.

While an outside micrometer may be used to measure the rod bolt length, the most accurate method is to use a specialty fixture that is outfitted with a dial indicator. Excellent examples of this gauge include units from ARP, GearHead Tools and Goodson Shop Supplies. GearHead’s bolt stretch gauge features a heat-treated aluminum frame (with a very handy thumbhole) with a specially modified dial indicator with sufficient spring tension to hold the gauge firmly to the ends of the rod bolt. The indicator can be rotated for right- or left-hand operation and the lower anvil is adjustable to accommodate various bolt lengths.

Goodson Shop Supplies also offers a rod bolt stretch gauge (P/N RBG-4) featuring spherical points for consistent and repeatable readings, and can also be rotated for right or left hand operation. Also, ARP offers its own bolt stretch gauge (P/N 100-9941) designed with 0.0005″ increments, with a heavy spring and ball tips.
There is a debate among some engine builders regarding the validity of measuring rod bolt stretch, due to potential compression of the rod material as the rod cap is clamped to the rod. While this may be a consideration, the use of a stretch gauge remains the best and most practical method of accurately determining bolt load.

Connecting rod bolts can be viewed as high-tensile springs. The bolt must be stretched short of its yield point in order for accurate and, most importantly, repeatable clamping of the rod cap to the rod. Improper or unequal bolt clamping force can easily result in a non-round rod bore.

Stock, or production, rod bolts typically offer a tensile strength of approximately 150,000-160,000 psi. However, due to variances in bolt production, tolerances can be quite extreme with peak bolt stretch occurring anywhere from, say 0.003″ to 0.006″. If the installer uses only torque in the attempt to achieve bolt stretch, he runs the risk of unequal rod bolt clamping loads due to the potential inconsistencies between bolts.

High-performance rod bolts are manufactured to much tighter tensile strength tolerances. ARP, for instance, calculates each and every rod bolt for stretch, and the bolt packages include reference data to that effect. The instructions actually recommend that a specific amount of bolt stretch should be achieved on each bolt (ARP cites 190,000 psi as its nominal, or base tensile rating, with actual ratings much higher in some applications).

How can unequal/inadequate rod bolt tightness affect the connecting rod big end bore shape? Let’s cite an example: If one technician reconditions the connecting rods using torque value alone to tighten the rod bolts and another technician who is responsible for final assembly uses the bolt stretch method, the final result can be out-of-round bores. This is because of frictional variances that will be encountered. As a result, the assembler using the stretch method may achieve a higher clamping load on one or more bolts as compared to the loads imposed when the rod reconditioner torqued the nuts without regard to actual bolt stretch. When a bolt is tightened with dry threads, as much as 80 percent of the torque can be exerted because of friction as opposed to bolt stretch.

In a high-volume production rebuilding facility, technicians may not have the time to measure for bolt stretch. However, a slower-paced operation that is attempting to obtain maximum accuracy (for a race engine, as an example), is far better off using the stretch method instead of relying only on the torque method.

A set of connecting rod bolts’ instructions may list both a torque value and a stretch range, effectively giving you a choice of methods. Yes, tightening only to a specified torque value is quicker and measuring bolt stretch requires more time, but the best results will be achieved by measuring bolt stretch. So, unless you’re in a rush, take the time to measure stretch, tightening each rod bolt to the recommended stretch range. It’s all about the quest for precision.
RECOGNIZING AND UNDERSTANDING THE FRICTION FACTOR

Friction (underhead and thread area contact) is a variable that is difficult to control precisely. The best way to avoid friction variables is to use the stretch method when tightening rod bolts. The stretch method allows you to accurately control the all-important bolt preload, independent of friction.

Each time a bolt is tightened (to value) and loosened, the friction factor is reduced as the mating surfaces (threads and underhead) “wear” in. Eventually the friction becomes fairly constant during future tightening.

Considering this “evening-out” of friction, when installing a new rod bolt where the stretch method cannot be used (because of available space for the stretch gauge, etc.), the bolt should be tightened and loosened several times before trying to achieve final torque value. While the number of tightening/loosening cycles depends on the lubricant being used, ARP recommends when using its lubricant, five loosening/tightening cycles is sufficient.

If a bolt is tightened using straight torque, you may not necessarily achieve the desired pre-load due to the variable of friction. Since we can’t predict the frictional loss, measuring rod bolt stretch provides the most accurate method of ensuring that the clamping loads will be both sufficient for the task and that each pair of rod bolts will achieve equal loads.

Bolt stretch is generated by a number of factors, including tensile strength and mass (the length of the bolt being stretched). The effective diameter of the bolt contributes to this. For example, let’s consider two 3/8″ x 1″ bolts. One features a 1″ long shank with threads on the full 1″ of the shank length. The other bolt features 3/4″ of shank length that is full-diameter and smooth, and only 1/4″ of thread length at the tip. The bolt with partial thread will stretch less because the shank area between the head and nut engagement area has a thicker cross section. The partial-thread bolt will have a .375″ diameter shank, while the all-thread bolt will have only a .324″ shank (due to the smaller root diameter inside the thread path).

ARP, to cite one example, calculates the stretch number for every bolt. On the spec sheet that is included with every bolt set, this stretch goal is listed, in addition to a torque value, but the torque value should be used as a guide only. ARP does not want the installer to use a torque value as the final indication of bolt stretch. Rather, the bolts should be individually measured for stretch, to assure that each bolt is installed at its optimum strength.

While we cannot control the reaction of the connecting rod base material, at least consider the potential compression of the connecting rod material itself during bolt clamping. As the bolt is tightened, the head of the bolt will tend to embed itself into the rod, slightly compressing the stock material of the connecting rod under the bolt head. Production rods are typically softer, allowing the head of the rod bolt to sink into rod until the material under the bolt heads “work hardens” under compression. ARP recommends that the bolt stretch is based on the bolt itself and not on the compression of the rod since we can’t accurately predict what the rod does in this state.

Since too many variables exist in terms of rod bolts and connecting rods, we can’t draw any generalized conclusions regarding ideal connecting rod bolt stretch. However, to use the Chevy smallblock 350 as but one isolated example, ARP typically looks for an installed bolt stretch of .0063″. Since each engine/rod/bolt application differs, we cannot assume that ideal bolt stretch would be the same for any given application.
ROD BOLT STRESS RISERS

Fatigue failure is frequently caused by local stress risers, such as sharp corners. In bolts, this would correspond to the notch effect associated with the thread form. It is well known that maximum stress in an engaged bolt occurs in the last engaged thread. By removing the remaining non-engaged threads, the local notch effect can be reduced. This leads to the standard configuration used in most ARP rod bolts-a reduced diameter shank and full engagement for the remaining threads. Providing a local fillet radius at the location of the maximum stress further reduces the local notch effect.

The reduced shank diameter also reduces the bending stiffness of the bolt. When the bolt bends due to deformation of the connecting rod, the bending stresses are reduced below what they would otherwise be. This further increases the fatigue resistance of the bolt.

The direct reciprocating load is not the only source of stresses in bolts. A secondary effect arises because of the flexibility of the rod big end. The reciprocating load causes bending deformation of the bolted joint (rod to rod cap). This deformation causes bending stresses in the bolt as well as in the rod. These bending stresses fluctuate from zero to their maximum level with each crankshaft revolution.

[DorianL]

[grumpyvette]

are those the 7/16" rod bolt versions??

whats strongest the (H) or (I) beam connecting rod design?
a great deal depends on the materials used, an (H) beam can generally be built a bit lighter in weight than a (H) beam design for a given power level but at some point the increased stress levels make the use of a very strong (I) beam design mandatory, the (I) beam design will tend to be heavier but slightly stronger, than an (H) beam that fits into the same size space.
but in most applications its more about materials used the true cross sectional area and the rod bolts than the connecting rod design.
Ive had zero problems with either design building 700hp-800hp big block engines so Im not saying I feel either designs got a noticeable edge.
shop carefully and look over your choices, it the design and materials and care in manufacturing that maters most of the time!

http://cp-carrillo.com/Tech/RodTech/tab ... fault.aspx

http://www.dsmtuners.com/forums/article ... ining.html

http://www.enginebuildermag.com/Article ... _rods.aspx

I would never personally re-use stock connecting rods without upgrading the rods with a careful polish resizing, shot peening, and bead blast, then,upgrading to ARP wave-lock rod bolts, but that is fairly expensive in most guys eyes, and in my mind the re-use of stock rods with pressed in pins,is a total waste of time, as I vastly prefer far stronger 7/16" ARP rod bolt SCAT rods with the full floating pistons,pins and 4340 forged rods that allow easy self assembly and reassembly during the often repeated clearance checking procedures.
Polishing the side beams,connecting rods and removing the surface roughness, helps prevent crack formation, from surface irregularity's and stress concentrating flaws in the surface,

the reason is simple, by the time you pay to have the much stronger ARP rod bolts installed on stock rods and have them polished to remove stress risers the average machine shop parts and labor cost equals or exceeds the cost of the far stronger SCAT aftermarket rods, yes they may require you rebalancing the rotating assembly to use them, but so will adding new pistons to old rods, or even polishing old rods in a few cases.

http://www.superchevy.com/how-to/74038- ... ting-rods/

http://www.fordmuscle.com/archives/2007/12/400Rods/

http://www.hotrod.com/how-to/engine/cho ... ting-rods/

http://scatcrankshafts.com/


CHEVY FORGED 4340 I-BEAM
With ARP 8740 7/16" CAP SCREWS
CHEVY SMALL BLOCK I-BEAM RODS with 7/16" CAP SCREW BOLTS
Part No Short No Description Rod Length Crank Pin Wrist Pin B.E. Width Weight
2-ICR5700-7/16 25700716 BUSHED 5.700" 2.100" .927" .940" 590
2-ICR6000-7/16 26000716 BUSHED 6.000" 2.100' .927" .940" 605
2-ICR6000-2000-7/16 26001716 BUSHED 6.000" 2.000' .927" .940" 605
2-ICR6125-7/16 26125716 BUSHED 6.125" 2.100" .927" .940" 610
2-ICR6125-2000-7/16 26126716 BUSHED 6.125" 2.000" .927" .940" 610
2-ICR6200-7/16 26200716 BUSHED 6.200" 2.100" .927" .940" 620
ARP 8740 7/16" CAP SCREWS
2-ICR5700-7/16A 25700716A BUSHED 5.700" 2.100" .927" .940" 590
2-ICR6000-7/16A 26000716A BUSHED 6.000" 2.100' .927" .940" 605
2-ICR6000-2000-7/16A 26001716A BUSHED 6.000" 2.000' .927" .940" 605
2-ICR6125-7/16A 26125716A BUSHED 6.125" 2.100" .927" .940" 610
2-ICR6125-2000-7/16A 26126716A BUSHED 6.125" 2.000" .927" .940" 610
2-ICR6200-7/16A 26200716A BUSHED 6.200" 2.100" .927" .940" 620
ARP 2000 7/16" CAP SCREWS
CHEVY BIG BLOCK I-BEAM RODS with 7/16" CAP SCREW BOLTS
Part No Short No Description Rod Length Crank Pin Wrist Pin B.E. Width Weight
2-ICR6135-7/16 26135716 BUSHED 6.135" 2.200" .990" .992" 780
2-ICR6385-7/16 26385716 BUSHED 6.385" 2.200" .990" .992" 785
2-ICR6700-7/16 26700716 BUSHED 6.700" 2.200" .990" .992" 810
ARP 8740 7/16" CAP SCREWS
2-ICR6135-7/16A 26135716A BUSHED 6.135" 2.200" .990" .992" 780
2-ICR6385-7/16A 26385716A BUSHED 6.385" 2.200" .990" .992" 785
2-ICR6700-7/16A 26700716A BUSHED 6.700" 2.200" .990" .992" 810
ARP 2000 7/16" CAP SCREWS
CHEVY LS-1 I-BEAM RODS with 7/16" CAP SCREW BOLTS
Part No Short No Description Rod Length Crank Pin Wrist Pin B.E. Width Weight
2-ICR6100-927 26100927 BUSHED 6.100" 2.100" .927" .940" 595
2-ICR6100-944P 26100944P PRESSED 6.100" 2.100" .944" .940" 600
ARP 8740 7/16" CAP SCREWS
2-ICR6100-927A 26100927A BUSHED 6.100" 2.100" .927" .940" 595
2-ICR6100-944PA 26100944PA PRESSED 6.100" 2.100" .944" .940" 600
ARP 2000 7/16" CAP SCREWS
yes much of that labor could be done at home if you have the correct tools and know whats required,
http://www.summitracing.com/parts/arp-134-6403



http://www.summitracing.com/parts/sca-2 ... /overview/

YES READING LINKS AND SUB LINKS HELPS A GREAT DEAL HERE

viewtopic.php?f=53&t=6909&p=22571&hilit=floating+pins#p22571

viewtopic.php?f=53&t=978&p=1711&hilit=floating+pins#p1711

[DorianL]

Eeeeek! Yer scarin' me. Will check once I'm home. For power claims made I had assumed they would be. Grmbl. Finely machined tho'.

[grumpyvette]

GRUMPY? A FRIEND gave me a 350 block with a Forged Steel crank that has never been bored over.
, since it's a Steel Crank I figured it must be an early 350, I'm going to try and keep it stock but I want it to last a long time. I am going to bore it 30 over, but it didn't have any rods when he gave it to me. What's a good OEM rod to use? Did they come with Forged Steel pistons too?


IM OFTEN ASKED WHY I DON,T REBUILD CHEVY CONNECTING RODS, WELL MAYBE A PICTURE WILL HELP,

a good set of SCAT FORGED 4340 forged connecting rods costs less than $400 and they are 150%-200% stronger than MOST OEM chevy SBC rods
it will cost you almost that much to replace the bolts with ARP wave lock bolts, balance and polish and resize stock rods and you have far weaker rods when your done


ok first ALMOST ALL factory Small block connecting rods are inferior in strength to reasonably priced aftermarket connecting rods, so I would strongly suggest buying new connecting rods, ones with cap screw 7/16" ARP rod bolts which could very easily be 200% stronger than factory 3/8" rod bolts, and OEM rods.

Chevy Small Block V-8s

The 327 and 350 small blocks use rods measuring 5.7 inches c-c with a 2.1 inch crankshaft pin and a 0.927 wrist pin, and weigh in at 630 grams. The larger 400 small block's rods are identical but for their 5.565-inch c-c length. Small block 283 rods measure 5.7 inches c-c, 2.00 inches on the crankshaft end and 0.927 inches on the wrist pin and weigh 655 gram
no one can see the rods in the engine so you should buy the strongest rods you can afford, remember youll need to have the whole rotating assembly balanced before you assemble the engine!
GM has a 5.7" rod kit now sold as part number 12495071, (for 8 connecting rods) which they use in the LT! and LT4 Vette engines as the replacement for the old "pink" rods. part number 12495071, should cost under $350 a set. They can go up to 500hp.
but keep in mind that $350 cost for the chevy rod set, is BEFORE you install stronger ARP rod bolts and have the connecting rods polished to remove surface flaws and by the time thats been done the cost will exceed $500 a set MINIMUM, for significantly weaker rods
http://paceperformance.com/i-6254565-10 ... ement.html
I generally GIVE these away too friends If I,m rebuilding a SBC,engine that has them, and won,t use them personally because by the time you get them rebuilt the cost more and are significantly weaker than aftermarket rods[/size]

Description
Single replacement connecting rod. Premium quality GM rod used in the LT1,LT4 and all GM performance parts small block crate engines. These rods are the replacement for the old "pink" rods. Single rod should only be used to replace another powdered metal rod due to differences in weight between older type rods, balance will be affected. These rods weigh 603 grams and are rated for 500 horsepower.


The old pink rods are fine to use, and GM used them in the ZZ-ZZ3 engines (part number 14096846),Pink' rods are GM 1038 forged rods that have been shot-peened and Magnafluxed, they are some of Chevys best production rods and were rated to 500hp and 6000rpm

viewtopic.php?f=53&t=1168

http://www.cnc-motorsports.com/connecti ... cting-rods.[/color][/b]html

RODS LIKE THESE are CHEAP AND STRONGER than CHEVY RODS. (ABOVE) [/color][/b]
http://www.summitracing.com/parts/sca-25700716


RODS LIKE THESE are STILL CHEAPER AND MUCH STRONGER THAN STOCK CHEVY RODS.



RODS LIKE THESE ARE ABOUT THE SAME COST AS REWORKED PINK OEM RODS BUT MUCH STRONGER THAN STOCK CHEVY RODS, EASILY 200% STRONGER.
http://www.summitracing.com/parts/sca-6570021
you would have few if any issues running these up to over 1000rpm and 200-250hp further than the chevy rods
RELATED INFO

viewtopic.php?f=53&t=1110&p=5644#p5644

viewtopic.php?f=53&t=341

viewtopic.php?f=38&t=3900&p=28672&hilit=balancing#p28672

viewtopic.php?f=53&t=510

viewtopic.php?f=53&t=204

viewtopic.php?f=53&t=1110&p=5644&hilit=pink+rods#p5644

viewtopic.php?f=53&t=1168

viewtopic.php?f=53&t=3540

displ..bore....stroke
262 = 3.671" x 3.10" (5.7" rod)
265 = 3.750" x 3.00" ('55-'57 Gen.I 5.7" rod,
'94-'96 Gen.II 4.3 liter V-8 "L99" 5.94" rod)
267 = 3.500" x 3.48" (5.7" rod)
283 = 3.875" x 3.00" (5.7" rod)
293 = 3.780" x 3.27" ('99-later "LR4" 4.8 Liter Vortec)
302 = 4.000" x 3.00" (5.7" rod)
305 = 3.740" x 3.48" (5.7" rod)
307 = 3.875" x 3.25" (5.7" rod)
325 = 3.780" x 3.62" ('99-later "LM7" 5.3 Liter Vortec)
327 = 4.000" x 3.25" (5.7" rod)
350 = 4.000" x 3.48" (5.7" rod)
350 = 4.000" x 3.48" ('96-'00 Vortec, 5.7" rod)
350 = 3.900" x 3.66" ('89-'95 "LT5" in "ZR1" Corvette 32-valve DOHC)
(5.74" rod)
350 = 3.900" x 3.62" ('97-later Gen.III "LS1")(6.098" rod)
(actually totals 346 cubic inches)
364 = 4.000" x 3.62" ('99-later "LQ4" 6.0 Liter Vortec)
383 = 4.000" x 3.80" ('00 "HT 383" Gen.I truck crate motor) (5.7" rod)
400 = 4.125" x 3.75" (5.565" rod)

Two common, non-factory, smallblock combinations:

377 = 4.155" x 3.48" (5.7" or 6.00" rod) 400 block and a 350 crank with "spacer" main bearings 383 = 4.030" x 3.76" (5.565" or 5.7" or 6.0" rod) 350 block and a 400 crank, main bearing crank journals cut to 350 size