GM Main Bearing Experts-----Help!

[TurboDave]

I don't plan on re using these, but I'd like to determine what's and why's of the markings. These are the mains that came out of my original factory block.
I listed the markings as on the passenger side or driver's side (passenger side being the tang side) because the markings were on two sides.

Can anyone deciefer these numbers so that I know what sizes to start with at first?? It's obvious which bearing halves are .001 under (Top #1, and Top #3) but are there others that are hidden in the numbers??


TOP #1 driver's side--6-5...................passenger side--GM66, .001 u.s., 1-86
Bottom#1 dr side--31Q632.................pass. side--GMM400, 18001493

Top #2 dr side--3806........................pass. side--57691, GMM400
Bottom#2 dr side--57691, GMM400......pass.side--3806

Top #3 dr.side--001, 65G631..............pass.side--GMM400, 180011491
Bottom#3 dr.side--08798, GMMA.........pass.side--48L6

Top #4 dr.side--57692, GMMA.............pass.side--50B6
bottom #4 dr.side--339C5...................pass.dide--57692, GMMA

 

[TurboDave]

OH, and here's a followup in case anyone wants to pipe in with suggestions. please.

The crank has been polished and the journal measurements are:
#1 main------2.4993
#2 main------2.4993
#3 main------2.4993
#4 main------2.4994
With no discernable taper

#1 rod journal------2.2486
#2 rod journal------2.2485
#3 rod journal------2.2485
#4 rod journal------2.2485
#5 rod journal------2.2486
#6 rod journal------2.2486
Also, no discernable taper

With the above measurements, what would you recommend for bearings??? mix and match mains to what the old ones were?

Rod journals are just a "smidge" under spec so may require .001 bearings, agree? disagree?

 

[Mike Licht]

Dave since different manufacturers use slightly different shells they only way is to put the bearings in the block and rods, torque them down and measure
Mike

 

[Mac in SD]

Dave,
Looking at your measurements, the rod journals are at or just below the stock range and the mains are real close to the 2.4995 spec. I'd order .001 under, and go from there. Mix-match was good enough from the factory, right?

 

[TurboDave]

Dave,
Looking at your measurements, the rod journals are at or just below the stock range and the mains are real close to the 2.4995 spec. I'd order .001 under, and go from there. Mix-match was good enough from the factory, right?

I think you're right. As soon as my cam bearings come in, I'll get them installed, and then put the (std) mains in and see how they measure up. If need be, I'll get Mike to send me a set of .001's and match what I took out.

I'd re-use the one's I took out, but one or two have a piece or two of suspicious looking material imbedded (I think).

I installed the rod bearings yesturday, and they all came out at .0017 to .0020 clearances.