327 main cap mix up!!

10062 Views 6 Replies 5 Participants Last post by Dave Koehler, Jun 27, 2009

327nova373

Discussion Starter · Jun 25, 2009

OK i just started putting a 327 i have two sets of main caps. set one casting numbers 3951 on all of them then on each one 490,492,536,537. set two 3951 then 21,19,19,43. could anyone tell me which ones are for the motor and what order they go?? vin on block 3903352.

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eloc431962

· #2 · Jun 25, 2009

I always mark mine before i remove them, with a punch or use the punches with the numbers on them for easy id when going back together so they dont get mixed up. If they werent marked before removal ther is no way to know where they went or what order. sorry. Cole

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eloc431962

· #3 · Jun 25, 2009 (Edited)

Have you checked real good to see if the main caps are already numbered. like 1-2 -3 and so on look on the side of the main cap. Was the rod caps marked before removal? You might as well get align hone to straighten out the mistake you made when you accidentally mixed up the unmarked main caps. That is why the first thing you should do before disassembling an engine is mark the main caps and rods to prevent this from happening. JMO, just trying to help your not the first person this has happened too. Cole

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327nova373

Discussion Starter · #4 · Jun 26, 2009

i bought it without the caps on it and i got two sets he said he doesn't know which ones came off the motor. one of the sets has the bolts with it and they're to long so i'm ruling them out. i'll look and see if they have any markings anywhere thanx

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BogiesAnnex1

· #5 · Jun 26, 2009

327nova373 said:
OK i just started putting a 327 i have two sets of main caps. set one casting numbers 3951 on all of them then on each one 490,492,536,537. set two 3951 then 21,19,19,43. could anyone tell me which ones are for the motor and what order they go?? vin on block 3903352.

No they came in sets machined specific to each engine. The numbers indicate fits to the block of origin but the block most likely doesn't have corresponding numbers since the fit is caps customized to the block.

A shop can probably figure this out by putting a crank mandrel down the main bore and seeing where which caps provide the best fit. You could do this yourself with the crank instead of a mandrel if your confident of your ability to divine good from bad fits. The basic test is how the cap fits any given block register and do the cap bolts just drop in without being offset or at angles. The register fit should be tight but not forced no more than rubber hammer tight and certainly not loose. Then you look for front to rear match and side to side match, then the bolt drop test. If you can torque them up and keep 'em aligned, you getting warm. Then test the crank for spin it should rotate with some drag but be smooth all the way around. This is going to take a while as you have 8 interchangeable caps and 4 possible locations for each, plus 2 oil caps and one location. So expect to put a couple hours into try and fit. Write notes and id the caps as this will quickly get confusing if you don't. Once you get it pretty good, a shop can install an undersized (dimensionally larger in automotive shop speak) set of bearings and hone them straight and properly sized. As long as the caps register properly in the block, getting a straight line thru the bearing bores isn't too hard. But I'd recommend you deliver this pile to a trusted machinist, rather than doing it yourself.

Bogie

P.S. What about the rods, were the caps and shanks numbered so they can be re-matched on assembly or is this an OSIF moment?

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racecar100

· #6 · Jun 26, 2009

Find a set of caps that lined up very close at the parting joints and have it line hone will fix the problem. Cast number on the caps don't mean any thing. Done it so many times.

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Dave Koehler

· #7 · Jun 27, 2009 (Edited by Moderator)

Been through this with customer blocks at least once a year. Get a magnifying glass and good lighting. Start with the rear since it is the easiest. it will either line up in all planes or it wont. If neither set does you are dead in the water unless you can find more caps and hope one of them fits close enough to line bore.

For the others the magnifying glass comes in handy. You can have two caps that may appear to line up at the parting line but only one is exactly right. Use the glass, get close and look at the machine marks. The right one will have the boring lines match up going from the block to the cap. it takes some time if someone didn't number them because Chevy never bothered.

As it's an old one it likely needs line honed or bored anyway. When you go to the shop tell them your story and ask that your detective work be confirmed.

Have a safe race
Dave Koehler
******************************

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