Would anybody have the crankshaft bearing clearance for the main bearings and rods after they've been plastigauged for 71 429? Our engine is being rebuilt in the shop and they plastigauged it at 0004. Something happened and the engine tightened up and while hand turning the engine the bearings have messed up the crank. They are saying it is a bearing problem. Does this sound right? We aren't good with engines and we are learning. Thanks for your help.

 

ok i hope you read it wrong because .0004 is wayyyy too tight! mains for a street/strip car will work with .0029(+/-.0002) for the rods .0025(+/-.0002). if your reading the plastguage right then its possible you got the wrong size bearings, possibly for a cut crank. flip the bearing over what if any #s do you see? and remember everything must be spotlessly clean when assembling, so much as a tiny piece of dirt can ruin your whole day. also its critical to check crank endplay spec on this is 0.004-0.010 with a max of 0.012 no more! after the crank is torqued give it a whack with a mallet on the snout and on the rear to center the crank now with a dial indicator check your crank endplay. also on your rods side clearence must be checked also, if your unsure of anything grab someone who can help, id hate to see you lose a good 429. good luck

 

It read out at .004. We added an extra 0 by mistake. Here is a pic of the reading of the rod bearing. http://i141.photobucket.com/albums/r...ock/4294sc.jpg

Here is a picture of the crank bearing. The picture isn't very good though.

http://i141.photobucket.com/albums/r...ankbearing.jpg

 

I can't see it binding up with .004 clearance. That's pretty loose in my mind. Clearances when I build my motors are from .001 to .0015 on the mains. On the rods, I'll go as far as .002. Any more than that, and I don't like it. Did he line bore/hone the mains? There are a number of things that will put it in a bind, like said already, side clearances.

I don't like second guessing people but, it sounds like they got in a hurry. Engine building is a process that has to be checked at every step along the way....after every bearing..you can't put in 6 bearings and then spin the motor to find it tight. You'll have to undo 6 bearings to find the one that made it tight. (although that's not possible with rods)

Also, if the bearing caps are not "round", you may have .004 in the middle where you show plastic, but a lot less on the "side". (by the bearing split)

 

If they were using standard size bearings and didnt clean the mating surfaces of the caps and block that could cause tight bearings. like already mentioned one little bit of dirt can be bad between any metal. I built a 2.3 four banger and got myself in a hurry one evening and noticed upon tightening each cap the bugger was getting tighter on the stand after every one. I stopped, took it all apart and realized i overlooked polishing the mate surfaces. I usually use 0000 steel wool on caps and block just that little bit of residue made the difference. as mentioned you cant be too fussy! clean clean clean.

 

Try using red or green plastigauge, also that stuff isn't too accurate, it should really be mic'd. 4 is loose for mains.