I was looking a some rod bearings on a parts engine and was trying to figure out what size they are by the numbers on the bearing shells does anyone know if the numbers on the shells will tell what size they are.The shells have thease markings GMMA 8587 175N8 .The engine is a 235 from I think 1958
That appears to be a GM factory number, not an aftermarket replacement. It's most likely to be a "standard" size, 2.3125" shaft size, but the only way to be sure would be to measure the crankshaft. Undersize replacements would be marked with a 10, 20, or 30, etc. indicating a reground "undersize" shaft diameter. A close, but not necessarily exact measurement can be done with a dial caliper- - - -for less than $20.00 online, I can't think or a reason anybody's basic tool box shouldn't include one.
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That would be great if they are the original ,thought the numbers may have a code to the size ,next time I have the engine oil pan off I will measure .The pan is on as I am soaking the cylinder as one cylinder or maybe two are stuck.the bearing was off as when I got the engine I was told it threw a rod but only thing I found so far was a stuck valve and bent pushrod and the stuck cylinder as it sat before I got it .thanks Jerry
So far as I know all undersize bearings are marked so. Sometimes in ink and sometimes stamped. From the photo the bearing looks to be in good condition. You could stick it back in and check the clearance with some Plastigauge. That would tell you two things: if the crank is ground under size and if that bearing can be reused. I don't know what the lead time is on rod bearings but Mains are both expensive and some (55 2nd and earlier) are hard to find. Anyway you could have a new set on the way if you choose to replace them. You might find std. bearings harder to find than undersize. I bought 0.010 undersize bearings 2 years ago and they shipped right away.
If the crank is std. but worn 0.002 or so and still round, you might find 0.002 under bearings, saving a regrind. GM used to list these in the parts book. Failing that you could carefully shim the std. bearings with tapered shim stock if you can find that. I used up the last of mine shimming mains on another engine and haven't looked for more lately. It's a reliable method for setting clearances and sometimes necessary to save a crank compensating for sloppy machinists.
1951 3800 1-ton "Earning its keep from the get-go" In the DITY Gallery 1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
