The Stovebolt Site Forums The Shop Area Engine Shop Need help please concerning 235 main bearing size

I was in the process of replacing the main bearings in a 1960 235. the main bearings that came out of the motor had "001" stamped on them so that is what im ordered. But instead I recieved "STD" or standard size main bearings. My questions is would it be possible to use the "STD" size main bearings in place of the 001 bearings? Can anyone help me out on this? thanks

folks have viewed the thread, can anyone help out? thanks

You have to measure the crankshaft mains up and match them to the bearings then You can order the bearings to match there are different ways of doing it , the best thing to do is get a engine building book or if You know someone that has done that before he can help You .It's really important to get it right the engine will not last if You don't. Some times it's better to give some of the work to a professional.

Pete

Hy tracern1, people look at threads to see if they can answer a question, or to try and learn something, in either case expecting an answer in less than a half an hour is unrealistic at best. Using standard size bearings on a crank ground .001" undersize will give you at least .001" more clearance than the specifications call for, in effect you'd be starting from a worn position. Undersize bearings are actually thicker than standard bearings, it is the crank that has been ground "under" the factory standard size, therefore the undersize bearings must provide a hole smaller in diameter than the factory standard bearing to take up for the fact that metal has been removed from the shaft, hope that helps.

Its very unlikely that someone turned a crank .001 maybe.010. If the inserts are .001 thecrank probably had enough wear to accept them, which tells me it probably needs turned. Run your fingernail across the journal and if it doesnt slide smoothly turn the crank. And Plastic-Gauge is your friend.

Thank you for all the replies and advice. I really was not expecting a reply in under 30 minutes. It was just surprising to have so many views of the posting within 30 minutes and not a tid bit of info. I do have some experience with engine repair and building. I just completed a replica car last summer from the wheels up. I'm just not to fimiliar with the 235, yet The crankshaft is not damaged, nicked scratched or warped. And I found that the STD size bearing will work in place of the 001. I just found this in the 235 engine manual on page 8-23. I will plastigage the crank in the morning Again thanks for all the advice and hopefully this will help some of the folks who are viewing to "learn" .

The .001" and .002" undersize bearings are made to compensate for slight wear on a crankshaft that's still round and smooth. If you've got one that checks out on the high side of the oil clearance, or slightly over, the smaller bearings can keep the crank from having to be reground. On a 235 main bearing, shoot for an oil clearance of .0015" to .0025", with a maximum of .003". If it's .004" or more, the 1 or 2 under bearing might be needed. They're still listed in the Federal-Mogul catalog, but they might be a bit hard to locate.
Jerry

Many times GM built their engines with .001 and .002 bearings from the factory. For whatever reason the crank when originally turned was that much under so they had bearings to fit rather than turning the crank or scrapping the crank.

Have it measured to make sure that it is still .001 under and buy the appropriate bearings to go with it. You will be fine.

Thanks again for the replies and advice concerning the main bearings. I'm going out and checking the crank shaft agian this morning before replacing the bearings. thanks

Extra clearance in the main bearings will make for a leaky rear main seal. Ask me how I know!

OOPS! I mis-spoke (must be a politician, right?) There is not a .002" undersize bearing available, .001" only. The Federal-Mogul part number is 960M for the 1956-62 engines, followed by the undersize, like 960M-001 for instance. The old TRW number for the same bearing set is MS1721P. The F/M shim set that's reccomended is FSM 124S, if you choose to use it. Some people do, others don't.
Jerry

replaced the main and rod bearings this morning along with the oil pump. Plastigaged the mains and they were within tolerance. Primed up the oil pump. Cranked it up, the motor ran great with very good oil preasure. Took the truck for a test drive then checked everything over again. looks like the main and rod bearing swapped worked out great. And I did not need the shims that were sent with the main bearings. Advance auto sells the plastigage for about $4.00 . Thanks for all the help and advice.

that is a cool 38 chevy you have. How far are you on that project?