checking piston too valve clearance



checking piston too valve clearance

Postby grumpyvette » October 14th, 2008, 1:32 pm

I still use the strips of modeling clay about 1" square and .2" (two tenths thick) but one thing everyone forgot to mention so far is that you need to spray the piston and valve and clay strips with WD-40 to ensure the clay does not stick to any parts, otherwise the clay will tend to stick to the valve and piston allowing them to push the clay between them during the compression of its surface by the valve (exactly what its there for) and PULL ON THE SURFACE of the clay as the valve moves away during separation (because the clay tends to stick ever so slightly as the parts pull away from each other if you don,t)which tends to give a false slightly greater than correct clearance measurement
The ex will be closest between 20 & 5° BTC & the intake 5-20° ATC
Exhaust side
Rotate the engine between 20 & 5 degrees BTC & find the closest point
Intake
Rotate the engine between 5 & 20 degrees ATC & find the closest point

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most people tend to tell me Im wrong about that use of WD40 spray on the clay, until they try it both ways... yeah the difference is usually minor but five to 10 thousands difference is not rare if the parts are clean and dry versus sprayed with an oil mist Image
Id be a whole lot happier on a 6000rpm-7000rpm plus engine build, up if my piston to valve clearance, on my engine was .100-.120 inch minimum, clearance even if it required machining the piston valve pocket depth about .060 (don,t forget the valve edge to valve pocket edge clearance)
GET THE CLEARANCES WRONG OR OVER REV THE ENGINE AND BAD THINGS CAN OCCUR, as can ASSUMING THE CLEARANCES ARE CORRECT IF YOU DON,T CHECK
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One of the easiest and quickest methods thats a bunch
more accurate than the clay-method , would be to use

Acid-core solder (usually .120" thick )
or
Resin-core solder (usually .090" thick )

READ THIS LINK

http://www.fordmuscle.com/fundamentals/pistontovalve/index.shtml



With the solder-method , you don't actually need a degree wheel
..just the harmonic balancer timing marks and a 6" dial caliper

Turn the engine over till you are coming up to TDC-Overlap
with both the exhaust valve on its way to closing, and
the intake valve beginning to open

Turn the engine till you are about 1/2 inch from TDC ,
then rollout and straighten a piece of acid-core solder about
6 to 8 inches long ....then with headers off , look thru
#1 Cylinder's exhaust port with a penlite...take the solder
and place it thru the spark plug hole , placing solder
across the Exhaust valve piston notch...then hold solder at that
angle while someone slowly turns engine over to TDC-Overlap
and then past TDC until you "feel" you can pull out solder .

as you turn the engine over at TDC the exhaust valve will
touch or squeeze the solder to the valve-to-piston clearance
...as you keep turning engine past TDC-Overlap,
the solder will be released

remove the solder and look for indentation ...measure with
dial-caliper ..and this is the valve-to-piston clearance !
No clay mess , no clay spring-back , very much accurate than clay-method

Cut a new piece of solder ...and just repeat for intake side !

Note=>can use solder method to check total deck heights accurately !
----------------------------------------------------------------------

the best method would be to use a 1.000" dial indicator and
magnetic stand ....bolt a 1/8 thick small plate to valve cover
bolt hole then stick the indicator in place on the steel plate .
(sometimes a SBC fuel-pump cover works great)

attach a degree wheel and pointer and find true TDC ,
then turn engine over till 10 degrees BEFORE TDC-Overlap
to measure Exhaust clearance . (8 -to- 12 deg closest points)

at 10 deg BTDC ...place the 1.000" dial indicator's point on
the flat part of the spring retainer , zero the indicator,
and with the set-screw backed out of the adjuster nut, take
a wrench and turn the adjuster nut till you force the valve to
bottom out against the piston's exhaust notch ....read how much
the dial indicator traveled ...thats your Exhaust clearance

back-off Exhaust adjuster nut back to ZERO point on dial indicator

now, repeat the same proceedure on the Intake side ...but this
time turn engine past TDC-Overlap to 10 degrees AFTER TDC
then check Intake clearance .
--------------------------------------------------------------------------

Note : You should always check valve-to-piston clearance with
a fully assembled valvetrain with the real springs in place
and every rocker lashed ...and ONLY turning the engine over in
the direction of rotation (ClockWise).

using light checker type springs will make you flycut pistons
approx. .030" more than necessary ...in other words, what ever
valve-to-piston clearance you check with lite-springs, when the
engine is fully assembled with the real springs, it will have
approx. .030" more clearance !

using lite-checker springs will be a "SAFER" way to check and will
be a good method to use for a beginner engine builder !!!

-------------------------------------------------------------------------
A professional engine builder would use the real springs and watch this
effect upon the cam-twist, Jesel belt distortion, pushrod flex , ETC.

A professional engine builder would check each and every Cylinder's
clearance..and have detailed computer records of things like
1- Piston Intake and Exhaust flycut valve notch depth
2- Piston Valve notch flycut radius , angle + tilt, center-to-bore location
3- Intake and Exhaust valve seat depths on heads, valve margins, etc.

and other things like
4- Total Valve-Notch-Depths

to check the Total Notch Depths ...just place each piston at TDC ,
then place dial indicator zeroed on the top of the valve stem ,
push the valve down till it rests ontop of the piston notch ,
then record this distance !

(need to have springs off , and 2 rubber O-Rings holding up valve
in guides ...when you go to check distance)

As you gain experience and information, you can easily know in advance
what the ballpark valve-to-piston clearance will be with known cam lobes and
rocker ratios , along with cylinder head's valve depth readings , and
piston flycut data .


I try for 0.080-0.120 on the intake and 0.100-0.120 on the exhaust as absolute minimums but am far happier with 0.120 thousands (just under 1/8") or greater on both!
Ill always trade increased clearance to gain reliability for a slight loss in compression,keep in mind that if you get to tight on those clearances you will be locked into that cam timing and dropping it back (RETARDING the cam) for greater high rpm power or (advancing the cam) for more low rpm torque becomes next to impossible in some cases while you tune the engine combo!
http://www.auto-ware.com/software/eap/eap.htm

theres software like I use in the engine shop but its reasonably expensive.............and I still check MANUALLY because I don,t trust software, yeah its usually close, but not exactly correct

ok first some facts, on piston to valve contact
the valves reach max lift at a time when the pistons not even neat TDC

heres a typical cam timing on a good hydraulic roller cam for a SBC that IVE used frequently

Crower_HR_00471_555_560.JPG


heres a cam timing chart

http://www.crower.com/valve-timing-chart


heres a crank rotation and piston angle chart
http://www.iskycams.com/ART/techinfo/ncrank1.pdf

simple math shows the intake valve reaches max lift near 118 degrees atdc
when the pistons about 3" down the bore
the exhaust reached max lift while the exhaust valve and piston were also reasonably far apart or almost 2.5" down the bore , valves tend to come closest to pistons at about 10- 20 degrees before or after TDC while not nearly at full lift and the duration and LSA of the cam had far more effect than max lift
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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: checking piston too valve clearance

Postby grumpyvette » October 14th, 2008, 1:33 pm

sure it can be done mathamatically if you care to take the time like we did in the old days

heres enought info to get you started

http://victorylibrary.com/mopar/piston_position-c.htm

http://www.iskycams.com/ART/techinfo/ncrank1.pdf


http://victorylibrary.com/mopar/deck-height.htm

http://www.crower.com/misc/valve_timing_chart.html

heres some loosely related info


what your looking for is the MINIMUM and MAXimum QUENCH distance that will allow operation with both effective SQUISH and no contact of the rotating assembly to the cylinder heads.
Id suggest a mnimum of .035 to allow for rod stretch and piston rock and a maximum of about .044-.046 to retain at least minimum squish to get that jet of super compressed a/f mix thrown into the central combustion chamber to cool and speed combustion, limiting the potential for detonation.
but Id also point out that theres very few factory engine running that tight on piston to cylinderhead clearances as the manufacturers are far more concerned with potential contact of rotating parts than getting the squish(quench) effect maximized
run less than about .035 thousands and at high rpm levels the pistons might hit the cylinder heads, run more than about .044 thousands the QUENCH effect of forceing the fuel air mix to the center of the cylinder from the cylinders edge area looses both speed and effectiveness, remember the quench area must be so tight that virtually all the fuel/air mix is forced into the center area and none is allowed to burn untill its squirted into the burn area increaseing turbulance and burn efficiency
in theory the much better quench, combined with the shorter more compact area the flame front needs to cover and the far higher turbulance combine to allow more of the pressure to build AFTER the crank passes TDC on the end of compression and begining of the power stroke

its mostly an advantage in that you get a more even burn in the cylinder and less chance of detonation.
look, it takes approximately 40 thousands of a second for the flame from the ignition to cross a 4.25" bore,at low rpms and still takes about 15 milliseconds at high RPM due to the much faster movement of the compressed fuel air mix in the cylinders, lets look at what that means
if the chevy plug is located 4/5ths of the way to one side thats a time of about 32 thousands for the pressure to build as the flame travels 3.4" in the chevy but in a compact combustion chamber it could only take the cylinder flame front less than 10-20 thousands of a second to travel acrossed the combustion chamber for a complete burn at low rpms, this of course speeds up as the swirl and turbulance increase with increased engine RPMs but the ratios stay similar. this results in more useable energy WORKING on the piston AFTER IT PASSES TOP DEAD CENTER ON THE POWER STROKE. BUT MODERN WEDGE combustion chambers use increased [b]QUENCH to speed the flame front and lower the burn time combined with a smaller combustion chambers look at this chart
http://www.iskycams.com/ART/techinfo/ncrank1.pdf

keep in mind that the cylinder pressure starts, builds to a peak and drops off all before the piston moves more than about 1/2 inch away from TDC and that if your wasteing 10-20 degrees of rotation compressing the burning mix in a slow to ignite combustion chamber your wasteing engine power
http://naca.larc.nasa.gov/reports/1939/naca-tm-914/

http://www.me.gatech.edu/energy/ICEngines/8_CylinderCombustionProcesses.pdf

http://www.nedians.8m.com/Comp_IC.html

http://mb-soft.com/public2/engine.html




LOOK CLOSELY AT THESE PICTURES
Image
you only have QUENCH if theres a flat area on the piston that mates to a matching flat area on the combustion chamber roof, on these pistons dual quench areas throw the compressed fuel/air mix to the center from the twin quench areas
notice, if used with this head, that only one side would have a fairly large and EFFECTIVE QUENCH area ,(the side away from the spark plug)
Image

things to read
http://chevyhiperformance.com/techarticles/94138/

http://www.theoldone.com/archive/quench-area.htm



http://racehelp.com/article_racing-10.html

Ive generally used KB HYPEREUTECTIC or SEVERAL BRANDS of FORGED pistons (mostly from SUMMIT,JEGS,or J&E and TRW, , getting tighter than about .036 quench[/b] has generally led to indications that the pistons have come very close to contact at times, I try to stay in the .037-.045 range simply because I personally feel that getting the max quench is FAR LESS IMPORTANT that avoiding piston to head contact.BTW I generally use AFTERMARKET (H) style rods, with 7/16" rod bolts by ARP and floating pin pistons and SELDOM build engines that exceed 7000rpm , theres not much to be gained in my opinion by spinning over 7000rpm except potentialy increased valve train problems ,if thats any help, and I generally use SOLID LIFTER CAMS in a serious 355 due to thier effective opperating rpm band (4500-7000rpm,Ive noticed that STOCK chevy 3/8" rod bolts on STOCK reworked rods DO TEND to stretch more!
I built a 355 with .028 quench and 12.7:1 cpr(ON REQUEST) that had light contact and needed to use thicker gaskets, so thats MUCH TOO CLOSE
look at this
http://www.vips.co.uk/demos/mech/con_rod/vm_anim.htm

BTW YES BEFORE YOU ASK...cylinders to cylinder variations should be minimized but don,t get crazy if some cylinders have a thousanth or so more or less, rods and pistons do vary in dimensions, don,t get crazy over a thousandth or so varriation

http://www.scegaskets.com/products/procopphd.html

these come in .021-.080 thick head gaskets in about .010 steps(youll need to order them)
Ive used them for years with zero problems on dozens of engines WITHOUT (O)RINGS, Im currently useing them on my corvette

BENEFITS OF copper HEAD GASKETS 1. Conductivity. copper is the standard by which all other conductors are measured. Therefore, a copper gasket provides superior thermal conductivity and stabilizes head and block temperatures which makes tuning easier. 2. 25% coefficient of elasticity. One of the properties of copper is that it stretches before a catastrophic failure, thereby providing an extra measure of safety in case of severe detonation. 3. Strength. copper (in the form we use) has a tensile strength of approximately 32,000 psi, compare this to the 1,200 to 1800 psi tensile of most facing materials used on conventional performance head gaskets.


Yes, they can be reused several times as long as there are no signs of failure, such as carbon tracking or corosion damage if they are carefully cleaned before reuse.
I have been useing SOLID COPPER HEAD GASKETS for years with aluminum heads on iron blocks (WITHOUT (O)rings) If your surfaces are strait and true and you correctly install them they work fine, now keep in mind that you MUST run high concentrations of anti-freeze and an anode in the radiator sure does not hurt to prevent electrolosis from causeing problems but I have never yet lost a head gasket and that includes nitrous use on several engines. now they sure are not your only option but they are a good one. btw I totally clean and degrease the block deck and head surfaces then spray the head gasket wet with COPPER COAT GASKET SPRAY then install them tacky wet and torque them down in 5LB stages to factory spec http://www.jcwhitney.com/productnoitem.jhtml?CATID=5131&BQ=jcw2 Image Image RADIATOR CORROSION INHIBITOR Prevents overheated radiators caused by rust, scale and corrosion. Save money on needless flushing, repairs, anti-freeze changes, special additives! Zinc anode slips in radiator filler neck and neutralizes rust/corrosion-causing chemicals. Lasts for years. NOTE: Not for radiators with plastic tanks.
SUMMIT RACING CAN ORDER YOU A SET


many, perhaps most copper head gaskets Ive seen and used are NOT embossed they are simply dead soft copper sheets with holes in the correct locations...unlike the comon stamped steel gaskets nost guys are familiar with, and again, let me point out I spray them down on both sides fairly heavily with copper coat spray then install them between a CLEAN and degreased block and heads and torque them down in stages

http://members.tripod.com/torquespecs/gmfs70-88chv8.htm

FELPRO engineers are no-doubt totally flipping and banging their heads on their desks, but I have used nothing but copperhead gaskets (with no (O) rings) on my engines for years, if you read the above links you get more info, the reason I used copperhead gaskets(installed that both sides heavily coated ,wet with copper coat spray by the way) is that I have never seen one leak or blow from cylinder pressure even when using nitrous. Now you must clean the block and totally degrease it, before you install those copperhead gaskets, he must coat both sides of the head gasket with copper coat spray, and you must torgue the cylinder head to the correct specification in stages, on my engines I usually use 35 lbs. 45 lbs. 55 lbs. 65 lbs as the stages and then go back a second time at the 65 lbs. level, each time I follow the correct torque sequence.( use the specifications that the cylinder head manufacturer suggests, if you're using studs instead of cylinder head bolts, they will be different, on aluminum heads you will need to use washers under the cylinder head bolts head, using studs you'll need washers under the nuts) http://members.tripod.com/torquespecs/gmfs70-88chv8.htm

For those of you don't know the torque sequence starts in the center and spirals outward on the cylinder heads so that you're always working in a spiral pattern from the center of the head towards the outside end of the cylinder head
now I am in no way saying that copperhead gaskets are the best or only solution but there are few parts that I have ever used that have worked as flawlessly with as few problems as copperhead gaskets have worked when applied soaking wet covered with copper coat spray on a properly degreased and cleaned block have worked for me over the years, especially with a heavy dose of nitrous. And yes it goes without saying that you will have to make sure that both the cylinder heads and block or correctly machined serfaces flat, clean, degreased, and would no crud/dirt/small-objects stuck to the head gasket cylinder head or block


heres an old post that will also be useful below

http://www.oliver-rods.com/products/InstallInstruct.html

http://www.raceeng.com/Pages/Page_7sc.html

http://www.carrilloind.com/install.html

rod bolt stretch gauges are the correct way to set the bolt loads, and the only way to get really close to exactly even stress,Image
BUT...theres HUNDREDS OF THOUSANDS of engines built every year with a correctly used TORQUE WRENCH,setting the bolts to the manufactures specified torque settings, and using the manufactures suggested procedures on those rod bolts,if the bearings are correctly clearanced and rods resized, magnafluxed, and clearanced and are correctly machined and clearanced, Ive seen extremely few failures that were caused by overtorqueing or incorrectly torqueing the bolts so they failed., again, Id say its more usefull if your planing to run on the ragged edge of engine part strength limits (and yes I use it,on race engines(rod bolt stretch gauge) ( but mostly because I spent the money to get one)youll be suprized at how close a correctly cerified torque wrench can get in skilled hands [/b]

arp makes 2 different head bolts, one is rated at 170,000 and the other at 190,000 ?

the cheaper bolts are still a big increase in strength over the standard production O.E.M. rod bolts, I would only use the better grade bolts in an engine that might see piston speeds EXCEEDING about 4500 FPM
keep in mind that rod bolts are critical and highly stressed, but also be aware that the comon AFTERMARKET (H) style rods are available with 7/16" arp rod bolts.
Image
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[/b]
now think about this
a comon small block rod has a 3/8" rod bolt with a about .1106 sq inches of cross sectional area or about a 18,800 lb failure limit with those 170,000 lb ARP rod bolts
a 7/16" rod useing ARP 170,000 grade bolts has about a .1505 cross sectional area or aproximately a 25,600 lb failure limit with those 170,000 lb ARP rod bolts, increaseing the rod bolt size effectively increases the rod bolt strength approximately 36% now if you figure in the fact that the aftermarket rods are significantly stronger,(ON AVERAGE AT LEAST 30%)and then figure that resizeing your stock rods and adding ARP bolts could easily cost $200 PLUS the cost of AFTERMARKET RODS EQUIPED WITH THOSE ARP ROD BOLTS IS NOT A BAD DEAL
personally, I only use STOCK RODS when Im doing NEARLY STOCK ENGINE REBUILDS
once Ive decided to exceed about 4200FPM piston speeds or about 475hp in a sbc it just makes economic sence to use better rods.

take that info and match it to your cam spec card
example


http://www.cranecams.com/index.php?show=browseParts&action=partSpec&partNumber=119661&lvl=2&prt=5
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: checking piston too valve clearance

Postby grumpyvette » October 14th, 2008, 1:41 pm

IF TWO CAMS HAVE IDENTICAL LOBE SPECS, AS TO LOBE SHAPE,LIFT AND DURRATION, EXCEPT FOR THE LSA, THE CAM IS GROUND ON, WHICH IS LIKELY TO HAVE TIGHTER PISTON TO VALVE CLEARANCES

heres two cams of identical design except the LSA
(112 LSA)
http://www.cranecams.com/index.php?show ... vl=2&prt=5

(106 LSA)
http://www.cranecams.com/index.php?show ... vl=2&prt=5

heres a piston rotation possition chart

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

a quick check of the cam timing figures shows the valves on the
112 LSA cams intake hit .020 lift at 29 degrees BEFORE TOP DEAD CENTER
106 LSA cams intake hit .020 lift at 34 degrees BEFORE TOP DEAD CENTER

the EXHAUST VALVE CLOSE ON THE 112 LSA cam at 31 degrees AFTER TOP DEAD CENTER
the EXHAUST VALVE CLOSE ON THE 106 LSA cam at 38 degrees AFTER TOP DEAD CENTER

so your correct IF YOU GUESSED that the TIGHTER LSA HOLDS THE VALVES OPEN LONGER AND IN CLOSER DISTANCE TO THE PISTON AS IT SWINGS PAST TDC

if you assumed a 5.7" rod,.023 deck and a true flat top piston with a .020 head gasket and the valve edge starting exactly .010 into the head from the heads deck surface youll see the valve is aproximately,.100 closer to the piston on the 106 LSA CAM on BOTH ENDS OF THE LIFT RAMPS
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: checking piston too valve clearance

Postby IBob » February 28th, 2010, 1:03 pm

Grumpy,

I'm trying to calculate piston to valve clearance.

Using the formulas I calculated that on a 383 with a 3.75 stroke and 5.7 rod, at 8* BTDC the piston would be .024" down from TDC. Is that correct?

Adding .045" quench (however obtained) that gives .069" clearance at 8* BTDC between the piston top and the head quench surface.

Using a cam that is 292/292, 230/230, .480"/.480", 109* LSA and 107* ICL, IO @.050 8* BTDC and EC @.050 4* ATDC

Intake valve lift at 8* BTDC would be 0" + .050" lobe lift (.075" valve lift) or 0" + .075" = .075"

On the intake I interpret this as at 8* BTDC there is negative, -.006" clearance between the piston and the valve, not counting the valve relief in the piston and valve recess in the chamber. How do you calculate the relief/recess amounts and incorporate them into the equation?


Exhaust valve lift at 8* ATDC would also be 0" + some amount less than .050" lobe lift ( ?? X 1.5 valve lift)
I don't know how to claculate the lift after the .050" closing, but befor absolute close.

Any assistance you could provide would be greatly appreciated.
IBob

 
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Re: checking piston too valve clearance

Postby grumpyvette » February 28th, 2010, 2:47 pm

Image
failure to verify clearances, verify valve train geometry , provide lubrication, and maintain cooling , stay out of DETONATION,or use of inferior components or exceeding your engines valve train control limitations, or red line on rotating assembly design strength can get darn expensiveactually measuring the piston to valve clearance in a temporarily assembled engine is the only reliable way you can be sure of your results, and that's best done once the cams been degree-ed into place,
Ive generally use a dial indicator,and a degree wheel, but its faster to use the 1/4" thick modeling clay, squares, sprayed with a bit of WD40 to prevent them from sticking, placed in the valve notches on the pistons and rotating the engine by hand with the head temporarily bolted in place, then use a dial caliper to measure the clay after sectioning it with a razor blade

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all valve clearances need to be verified during assembly , ideally with clay on the piston once the cams properly degreed in, the yellow clay shows valves close on the edge of the valve notch
http://www.islandblue.com/store/product ... -ASSORTED/

these threads hold more info, and the sub links are very useful

viewtopic.php?f=52&t=399&p=1689&hilit=+piston+valve+clearance#p1689

viewtopic.php?f=52&t=1769&p=4489&hilit=+piston+valve+clearance#p4489

viewtopic.php?f=44&t=554&p=1172&hilit=+piston+valve+clearance#p1172

viewtopic.php?f=52&t=528&p=654&hilit=+piston+valve+clearance#p654

http://www.fordmuscle.com/fundamentals/pistontovalve/

http://www.racingheadservice.com/Inform ... arance.asp

http://www.popularhotrodding.com/engine ... rance.html

http://www.carcraft.com/howto/116_0701_ ... index.html

http://www.centuryperformance.com/check ... g-144.html

http://www.cdxglobal.com/content/sample ... ear_WS.pdf

http://www.rehermorrison.com/blog/?p=186


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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: checking piston too valve clearance

Postby IBob » February 28th, 2010, 3:17 pm

I intend to check it when the engine is partially assembled, I just wanted to see if I could calculate it.

I read all of the thread and I personally like the solder method rather than the clay method, with the heads off.
IBob

 
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Re: checking piston too valve clearance

Postby grumpyvette » February 28th, 2010, 3:27 pm

IBob wrote:I intend to check it when the engine is partially assembled, I just wanted to see if I could calculate it.

I read all of the thread and I personally like the solder method rather than the clay method, with the heads off.



the potential problem with the solder route is that the solder needs to be located at the closest point of contact and that's NOT always in the seemingly obvious location, of the lowest tangential point on the valve circumference, because valve notches are rarely cut exactly matching the valve angle or head diam. or stem center-line

I was asked what threads to read to get the basics of engine building,
well the whole darn site was my first thought,
but heres a list to get you started and don,t forget the SUB LINKS and THEIR sub links
as theres a great deal of info to read, comprehend and absorb


as you get questions, use the search feature then post questions


viewtopic.php?f=69&t=519

viewtopic.php?f=69&t=629

viewtopic.php?f=44&t=38

viewtopic.php?f=51&t=125

viewtopic.php?f=59&t=1026

viewtopic.php?f=52&t=181

viewtopic.php?f=52&t=2746

viewtopic.php?f=52&t=389

viewtopic.php?f=53&t=247

viewtopic.php?f=53&t=2733

viewtopic.php?f=53&t=110

viewtopic.php?f=52&t=796

viewtopic.php?f=55&t=2739

viewtopic.php?f=51&t=588

viewtopic.php?f=52&t=90
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: checking piston too valve clearance

Postby IBob » February 28th, 2010, 3:32 pm

Understood, Thanks
IBob

 
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Joined: February 25th, 2010, 8:33 pm

Re: checking piston too valve clearance

Postby grumpyvette » August 27th, 2010, 10:16 am

don,t forget to carefully measure the radial clearance along the valves edge to the valve notch,many guys check the distance between the valve and piston but sometimes your valve is not nearly centered in the valve clearance notch and while there might be .180 between the piston and valve vertically there could be .005 or less along one edge and that almost always results in problems, try to maintain a .060 minimal radial clearance, you'll want to maintain a .060-.070 minimum being even better,on your valve edge to piston notch clearance in most cases as the valve descends into the valve notch recess, if the valve edge binds on the edge it makes little difference how much distance remains under the valve head to piston
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Reher-Morrison Racing Engines, posted this info
"Here is the method we use at Reher-Morrison Racing Engines. Not everyone may agree with our technique, and that’s all right. I am convinced, however, that it is the best way to achieve repeatable, accurate results.

First, put away your clay and your light-tension checking springs. The time-honored practice of mocking up a motor and putting clay in the valve pockets to measure clearance introduces too many variables to be trustworthy. The amount of clay on the piston top, the density of the clay, the effect that the clay has on the relative positions of the valve and piston, and the difficulty of measuring the thickness of the compressed clay accurately are just a few of the sources of potential error with this method. You don’t use clay to measure piston-to-wall clearance and bearing clearance, and you shouldn’t use it to measure valve clearance either.

You must use the same components when checking valve clearance that you intend to use when you assemble the engine. This includes the same lifters, the same pushrods, the same rocker arms, and the same valve springs. Light-tension checking springs simply can’t duplicate the load and deflection that the valvetrain experiences with stiff race springs. The difference in actual valve clearance between checking springs and race springs is typically .020 to .030-inch. If you set up your engine with checking springs with .075-inch intake valve clearance, the actual clearance with race springs will be closer to .100-inch.

The first step in the Reher-Morrison method is to determine whether the valve pockets are located properly. A discarded valve that fits your cylinder head makes an ideal tool. Cut off the head of the valve and turn the stem to a point. Preassemble the engine with your bare cylinder heads (remember to use a previously compressed head gasket), put masking tape on the ring lands to center the piston in the bores, a bring the piston to 10 degrees before or after Top Dead Center (it doesn’t matter which at this point) and drop your homemade punch into the intake and exhaust guides. Give the punch a gentle tap to mark the valve stem centerline on the piston and then remove the head.

To check the valve pocket location, remove the cylinder head and set a pair of calipers to the radius of the valve head (for example, for a 2.500-inch diameter valve head, set the calipers at 1.250-inch). With one point centered on the punch mark, swing the other point around the valve eyebrow. If the caliper hits the edge of the valve pocket, so will the valve. I recommend a minimum of .050-inch radial clearance between the edge of the valve and the pocket.

If the valve relief is located properly, you must then check its angle. Again, a discarded valve with the proper stem diameter makes an excellent checking tool. Weld or epoxy a small steel ball onto the edge of a steel valve. Mark the tip of the valve stem with a notch in line with the ball as a reference point. If your engine has two different valve angles – a big-block Chevy or Cleveland Ford, for example – you will need to make intake and exhaust checking valves.

Insert the checking valves into the bare head and install the head on the preassembled short block. Bring the piston to 10 degrees before or after TDC. Put a dial indicator on the tip of the valve stem and slowly rotate the valve with your fingers. If the stem rises and falls as the ball travels around the valve notch, the angle of the relief is incorrect. You can draw a “road map” by noting the position of the reference notch as you turn the valve. For example, if the valve stem rises near the top of the dome and falls at the bottom of the valve notch, then the angle of the valve relief is too steep. Using this technique, you can precisely determine how much material must be machined to correct the angle of the valve relief.

After you have established that the valves have enough radial clearance in their respective notches and that the angles of the valve reliefs are correct, you are finally ready to check piston-to-valve clearance. Assemble the short-block and cylinder heads with the valvetrain components you intend to use. Adjust the valve lash, set up a dial indicator on the valve spring retainer so that its plunger is parallel to the valve stem, and bring the piston to 10 degrees BTDC. Compress the spring on the exhaust valve and measure the movement required for the valve to contact the piston. (We used a tool similar to a valve spring tester with a solid bar instead of a flat spring to compress the valve spring.) Move the dial indicator setup to the intake valve, rotate the crankshaft to 10 degrees ATDC, and repeat the procedure.

This procedure and a little patience will ensure that your engine’s piston-to-valve clearance is measured correctly. The ideal clearance dimension for your combination will depend on the weight of your engine’s valvetrain components (especially whether you use steel or titanium valves), the maximum rpm, the tension of the valve springs, the characteristics of the camshaft, and other factors.

In most instances, off-the-shelf pistons have valve pockets that are too deep and provide much more valve clearance than is really necessary. This is perfectly understandable, because the piston manufacturers can’t anticipate every possible combination of cylinder head, camshaft, block height, valve height, gasket thickness, etc. They don’t want to hear from an angry customer who crashed all the valves in a new engine, so the piston makers typically machine the reliefs in shelf-stock pistons with clearance for the worst case scenario. Then to compensate for the oversize valve reliefs, the piston dome is made taller to produce the advertised compression ratio.

The downside of this situation is that overly generous valve reliefs cost horsepower. For example, a 2.50-inch diameter valve pocket that is .100-inch deeper than it really needs to be has a volume of 8 cc’s. That much volume at TDC can significantly lower the compression ratio, reducing efficiency and power. It’s much better to have the proper piston-to-valve clearance and a shorter dome that doesn’t intrude as far into the combustion chamber.

Imagine two engines with the identical compression ratio. One has pistons with valve reliefs that are too deep and domes that resemble Mt. Everest; the second has pistons with optimized valve reliefs and shorter, rounded domes. Both engines have the same volume above the piston at TDC, but the engine with the proper valve reliefs and shorter domes will have a substantial horsepower advantage.

Measuring piston-to-valve clearance properly is one of the basic operations that every novice engine builder should master. It’s not as sexy as flow bench testing or as high-tech as running dyno simulations on your laptop, but it is an absolutely essential step in building a reliable and powerful racing engine."


theres hundreds of ways to destroy an engine, but a common route is trying to compress solid objects in the combustion chamber,where theres not nearly enough clearance,
failure to keep the pistons from hitting the valves, bending valves, ,over reveing the valve train and having un-controlled valve movement, or having chunks of piston,that detonation can break loose, being compressed against the heads,can result in the cracked cylinders, and bent rods like the pictures below show
Image
Image
Image
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: checking piston too valve clearance

Postby grumpyvette » January 22nd, 2011, 4:16 pm

Security Clearance: Measuring Piston-to-Valve


Written by David Reher

With apologies to my sister the veterinarian, there is more than one way to skin a cat and more than one way to measure piston-to-valve clearance. I’m not an authority on cat skinning (nor do I want to be), but I do know about the importance of proper valve clearance in a racing engine. I see hundreds of engines come through our shop every year, and I’m alarmed by how many engines assembled by do-it-yourself builders have incorrect piston-to-valve clearance.

There are two ways to get it wrong. The first is usually catastrophic: If you have insufficient clearance, the pistons hit the valves, followed by the predictable parts damage. On the other hand, if you have too much clearance, the engine will run, but it won’t achieve anything close to its performance potential. In either situation, you’ve wasted time and money that could have been saved by checking piston-to-valve clearance properly.

Here is the method we use at Reher-Morrison Racing Engines. Not everyone may agree with our technique, and that’s all right. I am convinced, however, that it is the best way to achieve repeatable, accurate results.

First, put away your clay and your light-tension checking springs. The time-honored practice of mocking up a motor and putting clay in the valve pockets to measure clearance introduces too many variables to be trustworthy. The amount of clay on the piston top, the density of the clay, the effect that the clay has on the relative positions of the valve and piston, and the difficulty of measuring the thickness of the compressed clay accurately are just a few of the sources of potential error with this method. You don’t use clay to measure piston-to-wall clearance and bearing clearance, and you shouldn’t use it to measure valve clearance either.

You must use the same components when checking valve clearance that you intend to use when you assemble the engine. This includes the same lifters, the same pushrods, the same rocker arms, and the same valve springs. Light-tension checking springs simply can’t duplicate the load and deflection that the valvetrain experiences with stiff race springs. The difference in actual valve clearance between checking springs and race springs is typically .020 to .030-inch. If you set up your engine with checking springs with .075-inch intake valve clearance, the actual clearance with race springs will be closer to .100-inch.

The first step in the Reher-Morrison method is to determine whether the valve pockets are located properly. A discarded valve that fits your cylinder head makes an ideal tool. Cut off the head of the valve and turn the stem to a point. Preassemble the engine with your bare cylinder heads (remember to use a previously compressed head gasket), put masking tape on the ring lands to center the piston in the bores, a bring the piston to 10 degrees before or after Top Dead Center (it doesn’t matter which at this point) and drop your homemade punch into the intake and exhaust guides. Give the punch a gentle tap to mark the valve stem centerline on the piston and then remove the head.

To check the valve pocket location, remove the cylinder head and set a pair of calipers to the radius of the valve head (for example, for a 2.500-inch diameter valve head, set the calipers at 1.250-inch). With one point centered on the punch mark, swing the other point around the valve eyebrow. If the caliper hits the edge of the valve pocket, so will the valve. I recommend a minimum of .050-inch radial clearance between the edge of the valve and the pocket.

If the valve relief is located properly, you must then check its angle. Again, a discarded valve with the proper stem diameter makes an excellent checking tool. Weld or epoxy a small steel ball onto the edge of a steel valve. Mark the tip of the valve stem with a notch in line with the ball as a reference point. If your engine has two different valve angles – a big-block Chevy or Cleveland Ford, for example – you will need to make intake and exhaust checking valves.

Insert the checking valves into the bare head and install the head on the preassembled short block. Bring the piston to 10 degrees before or after TDC. Put a dial indicator on the tip of the valve stem and slowly rotate the valve with your fingers. If the stem rises and falls as the ball travels around the valve notch, the angle of the relief is incorrect. You can draw a “road map” by noting the position of the reference notch as you turn the valve. For example, if the valve stem rises near the top of the dome and falls at the bottom of the valve notch, then the angle of the valve relief is too steep. Using this technique, you can precisely determine how much material must be machined to correct the angle of the valve relief.

After you have established that the valves have enough radial clearance in their respective notches and that the angles of the valve reliefs are correct, you are finally ready to check piston-to-valve clearance. Assemble the short-block and cylinder heads with the valvetrain components you intend to use. Adjust the valve lash, set up a dial indicator on the valve spring retainer so that its plunger is parallel to the valve stem, and bring the piston to 10 degrees BTDC. Compress the spring on the exhaust valve and measure the movement required for the valve to contact the piston. (We used a tool similar to a valve spring tester with a solid bar instead of a flat spring to compress the valve spring.) Move the dial indicator setup to the intake valve, rotate the crankshaft to 10 degrees ATDC, and repeat the procedure.

This procedure and a little patience will ensure that your engine’s piston-to-valve clearance is measured correctly. The ideal clearance dimension for your combination will depend on the weight of your engine’s valvetrain components (especially whether you use steel or titanium valves), the maximum rpm, the tension of the valve springs, the characteristics of the camshaft, and other factors.

In most instances, off-the-shelf pistons have valve pockets that are too deep and provide much more valve clearance than is really necessary. This is perfectly understandable, because the piston manufacturers can’t anticipate every possible combination of cylinder head, camshaft, block height, valve height, gasket thickness, etc. They don’t want to hear from an angry customer who crashed all the valves in a new engine, so the piston makers typically machine the reliefs in shelf-stock pistons with clearance for the worst case scenario. Then to compensate for the oversize valve reliefs, the piston dome is made taller to produce the advertised compression ratio.

The downside of this situation is that overly generous valve reliefs cost horsepower. For example, a 2.50-inch diameter valve pocket that is .100-inch deeper than it really needs to be has a volume of 8 cc’s. That much volume at TDC can significantly lower the compression ratio, reducing efficiency and power. It’s much better to have the proper piston-to-valve clearance and a shorter dome that doesn’t intrude as far into the combustion chamber.

Imagine two engines with the identical compression ratio. One has pistons with valve reliefs that are too deep and domes that resemble Mt. Everest; the second has pistons with optimized valve reliefs and shorter, rounded domes. Both engines have the same volume above the piston at TDC, but the engine with the proper valve reliefs and shorter domes will have a substantial horsepower advantage.

Measuring piston-to-valve clearance properly is one of the basic operations that every novice engine builder should master. It’s not as sexy as flow bench testing or as high-tech as running dyno simulations on your laptop, but it is an absolutely essential step in building a reliable and powerful racing engine.
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Joined: September 14th, 2008, 1:40 pm
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