can I get it polished



can I get it polished

Postby grumpyvette » May 22nd, 2013, 7:47 am

"HEY grumpy I got a good deal on a new forged 454 crank, but the guy I bought it from purchased it for a project and had it sitting on a shelf for over 5 years and its got a few rusty finger prints on the journals, can it be used?"


Since its a FORGED crank, Id bring it to a good machine shop, for a close inspection,and measurement ,and get their opinion,a good machine shop that can check it out, and polish it if required,you could buy a cast crank for less than $300, a forged crank can easily cost more than double that money, so the $100-$170 most machine shops might charge to recondition the forged crank could easily be worth it, depending on the initial cost of the crank.
but in the majority of cases it can be polished or cut slightly under size, then it can be polished and will be fine,
get the machine shop to order the matching size clevitte (H) bearing set, and IF it was my project ID get the matching SCAT connecting rods pistons and rings, bearings, damper ,flexplate or flywheel, etc. and have the whole assembly balanced

[b] adding a couple high heat tolerance magnets to the engine helps trap, the metallic debris,the finer stuff gets easily washed into the sump with the oil flow, any parts failure like that generates BEFORE the abrasive grit gets sucked thru the oil pump and be aware the oil filter won,t always prevent 100% of the grit reaching the bearings.
IVE typically used several of these magnets in any engine,Ive built, one in the rear oil drain on each cylinder head, one near each lifter gallery drain and 4 in the oil pan sump

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http://www.kjmagnetics.com/proddetail.asp?prod=D82SH
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BE AWARE magnets heat tolerance differs so ask for and pay attention to the heat limitations, a MINIMUM of 300F for any magnet expected to be used bathed in hot engine oil would be smart
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when you get the crank polished take the time and effort to clean out any cross drill oil feed passages and to very carefully de-burr the passage opening edges, as this is a very commonly overlooked issue, below is what at first looks like a perfectly polished crank, with oil feed passages to the rod bearings,
but the deep scratches the oil feed passage openings left in the rod bearing surfaces bare witness, after a single rotation, during a trial assembly show they are HARDLY burr free or ready for use, and obviously he failed to check each rod bearing during the assembly process, and probably ignored , what was very likely un-even or rather excessive resistance to the crank rotation. which should never exceed about 40 ft lbs even with all 8 rod bearings and pistons installed

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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!!
grumpyvette

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Re: can I get it polished

Postby grumpyvette » June 12th, 2014, 8:23 am

Husam wrote:This my first engine build and the crank (scat cast crank)got scratched as I was blueprinting it
Can I assemble with this scratch that I can barely feel it with my finger nail.


very clear detailed pictures , taken in good light from several angles would be very helpful, but I suspect from the very limited info that some polishing time with a long strip of some 800 grit wet/dry sand paper followed by 1200 grit paper used under a section of leather belt for support , will remove the burrs , BTW always polish the journal surface away from the direction or rotation,and use some WD40 on the paper,and it won,t take more than 20 passes (10 with each grit) to do it if its damaged lightly enough that you don,t need a machine shop to clear it up, that might get you back operational,but be darn sure to clean carefully to remove micro grit, that might be left on the surface, but you must know a few things to do it correctly
Crankshaft Grinding and Polishing


federal mogal wrote:When refinished, the surface of a crankshaft will develop microscopic peaks which are “tipped” in the direction that the sparks spray during grinding (see the illustration above). If these peaks point toward the oil film area when the engine is running, lubrication is interrupted, and the bearing will show premature wear. It is important that the crankshaft be ground and final polished so that these peaks are tipped opposite the direction that the crank rotates when it is installed in the engine, this is referred to as the “favorable” direction. We recommend grinding the crank in the “favorable” direction, followed by a multi-step polishing process using progressively finer paper. The first polishing operation uses 280 grit paper with the shaft rotating in the reverse direction – this helps to “knock off” some of the raised material left over from grinding. The second polishing process uses 320 grit paper, and the crank should be rotating in the “favorable” direction. A third step polish with a very fine (400 grit) paper is optional, but should again be done in the “favorable” direction. If the thrust surface was contacted during the resizing operation it must also be polished.


HERES WHAT A MACHINE SHOP CRANK POLISHING BELT LOOKS LIKE

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care must be taken to ensure the journal does not get polished unevenly, tapered or egg shaped
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journal surface must be polished so micro burrs face away from the direction of rotation on bearing surface for max durability on bearing surface, burrs far to small too see or feel still induce wear
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yes you generally need to verify clearances and journal taper and measure bearing journal roundness but in many cases a bearing thats slightly tighter can match the journals required clearances without going to a .010-.020,.030 under size.
Id also point out that occasionally guys forget to clean out the cross drilled oil passages resulting in metallic debris embedded in the bearings so clean carefully after any crank journal polish work
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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!!
grumpyvette

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Site Admin
Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida


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