So what rod bearings are these?

My engine has 24K total miles and about 3-4K on a rebuild. The rebuild was done in 1965 and the engine was run to .060 according to the pistons.

I going through with a ball hone and replacing the rings and rod bearings, maybe the main bearings too.

I pulled my rod bearings and they say this on the outside:

FM 7 5
2020-AP

Can anyone tell me what they are oversize wise, or if they are oversize at all?

Thanks!

 

Rod journal has been turned .020" undersize, that's usually what that number denotes. What year and CID engine are we talking about?

 

Totaly WRONG dude!!
That is the Federal Mogul part # for a SBC rod bearing in STANDARD!! for a 2" journal crank ie pre 68. Undersize would be marked .0X0 either in a ink stamping or stamped into the shell. Sold this stuff for 30 years . The "AP" tells the bearing material in aluminum based.

 

Totally sorry to mis-inform. My mistake.

 

No problem ,gota learn sometime. I got a un-fair advantage, been doing this stuff over 50 years and pushed auto/truck parts for better than 30.

 

Thank you! That is exactly what I was expecting giving the low mileage of the crank.

So who makes the best rod/main bearings nowadays?

Alex

 

Thanks for the correction. Guess it's been awhile since I've seen an undersize shell. Apologies to all.

 

Before removing the crank from the block I'd measure the endplay using feeler gages or a dial indicator. If its much over 0.010 inch the crank thrust flange may be worn. I;d look at the finish of the forward facing flange anyway, especially for a standard trans application. Every time the clutch is depressed that flange gets forced forward. It needs to be smooth and in good shape.
Before buying any bearings I'd get the crank and rods magnafluxed (wet fluorescent method, not dry powder). No sense starting with a cracked crank. The "ring" test only identifies a REALLY badly cracked part. If anyone tells you they've never seen a cracked or broken Chevy crank, they've just been lucky.

Then I'd measure every rod and main journal 6 ways using a micrometer, not a vernier, looking for taper and out-of-round.
page 35 of Mahle/Clevite catalog EB-40-07 has recommended tolerances.
http://www.clevite.com/pubs_detail.asp?c=1&id=108
You can cheat a little on those, but not a lot.

It may be that 0.001 or 0.002" undersized bearings are more appropriate, or that the crank needs grinding.

I'd take a fine sharp metal file and gently file an edge of a counterweight or the face of a crank cheek. If the file just skates and does not dig in, it is probably TuffTrided, and a premium piece. Tufftrided cranks have a distinctive dark gray color when thouroughly cleanee, too.