Amc V8, Letters Beside Caps

Guys

Emptied the original 73 engine today, noticed letters stamped on passenger side of the main bearing caps

1: no stamp
2: C
3: D
4: D
5: C.

I'm hoping these dont denote oversize mains.

Mains were down to copper, except #3 which had a pretty deep debris stripe. Engine has 60k on odometer, whatever thats worth.

Thanks
Chilly

 

Look on the backside of the bearing, and you will know.

 

Back when the factories assembled engines by hand, clearances were checked properly. I’ll bet they are all standard size with only .001” difference. The assembler would select the slightly over or undersized bearing to achieve the specified measurement. I’ve never seen the bearing cap stamped to indicate this though. These small increment over/under bearings weren’t available as a service part. As stated previously the oversize should be stamped or inked on the backside of the shell.

 

was there a tag on the pass valve cover? I think if they are oversized from factory its marked on that tag.

 

Yep. That's in the TSM. According to the TSM, the stamps are not a factory marking scheme.

Buy an inexpensive micrometer and measure.

https://www.amazon.com/s/ref=nb_sb_...eld-keywords=micrometer&rh=i:aps,k:micrometer

 

AMC engines are infamous for odd-sized bearings from the factory, especially in the early to mid '70s. I have a 360 that had a mix of 0.0005 and 0.0003, and a couple other sizes on both rods and mains. I actually installed some back with a split set of 0.001 and std and it has been fine. Others, I re-used the original odd bearings as this was a very low-mile engine. Yes, I should have had the crank turned, but the factory "saved" a bunch of what I consider out-of-spec cranks by using now unobtanium odd sized bearings.
-Donny

 

Valve cover tag has no digits indicating over/under bearings.

Im fortunate to have been site quality leader when we set up a new factory, and insisted on Mitutoyo bore micrometers and Dorsey snap gauges that use miyutoyo digital indicators. As well as Mitutoyo OD digital mics, and analog where that makes sense. I can probably borrow the stuff that will legitimately measure to 0.00005" accuracy.