I finished disassembling and measuring my "mystery motor" last weekend, and was surprised to find out it looked pretty darn good inside.
The bearings show wear, but the good kind - nice and even, and not too much of it, with no scoring, burning, or other nastiness.

I plan to replace the shells, so I checked the numbers on the backs, to be sure I didn't have any undersizes. For the most part, none of the numbers corresponds to any part number that I can find.

I am interested in knowing what all those numbers DO mean, and, of course, in getting the right new bearings to replace the old ones.

First, for reference, my measurements:

• Main Journals:
  1. 2.4995
  2. 2.4990
  3. 2.4990
  4. 2.4995
  5. 2.4985
• Main Bearings - Plastigage:
  1. 0.0020
  2. 0.0025
  3. 0.0030
  4. 0.0018
  5. 0.0030
• Rod Journals:
  1. 2.1240
  2. 2.1240
  3. 2.1244
  4. 2.1244
  5. 2.1244
  6. 2.1255
  7. 2.1248
  8. 2.1248
• Rod Bearings - Plastigage:
  1. 0.0030
  2. 0.0030
  3. 0.0025
  4. 0.0030
  5. 0.0030
  6. 0.0025
  7. 0.0030
  8. 0.0030
• Rod Bearing Side Clearance - All - 0.0125"

Now, the bearing numbers...
All of the main bearing shells have four numbers, stamped across the back surface, parallel to the axis of the crank, with each one about ½" below the previous one.
For instance, the №1 shells read like this:
5458936
GMM400
0005
34H6

I assume that the "GM400" (or "GMMA" on some of them) is a code to identify the manufacturer and that the "34H6" is a date code.
That would leave the "5458936" as a part number, and the "0005" as a potential over or undersize marking.
The manual states that undersizes will be marked by letters stamped on the tang, and, in fact, my №5 bearing has an A with a circle around it right on the tang on both halves.
The problem is that I have looked up all of the GM part numbers for these bearings, and none of them is the same as the numbers stamped on the backs of the shells, which offends my sense of order.

Here are the "part" numbers on my main shells (some halves have different numbers from each other), along with the potential "date" and "undersize" numbers:

1. 5466_89....5458936....10B6....34H6....0005
2. 5458936....5458936....34H6....34H6....0005
3. 57707.......57701........35605..29X6
4. 5458937....5458937....301B6....314G5....001
5. 57703.......57703........1006....49P6

As for the rod shells, they all have the same "part" number, 2623332 (GM part number should be 5474130), and the same "GMM400" code.
Interestingly, the alphanumeric code varies with the side of the engine:
Even cylinders are 54-G, Odd cylinders are 36-E.

On a separate note, and to see if you're paying attention, the cam bearings all look good, ie: not worn or scored, but the upper surfaces of all of them are rough with what appears to be brown baked-on oil deposits. Is this a sign of anything bad? Do they need to be changed, or should they just be cleaned?

Thanks for reading this far, and for any insights you may have!

- Eric

 

The 1970 Olds Engine Assembly Manual lists some of your bearing part numbers as being factory-installed on 350s that year -- which means they were probably used in other years as well. In particular:

548936 was used for .0005 undersize on #1 upper and #2&4 upper for the Qx and QD code engines. It was also used on #2&4 lower for all the 4 bbl (high-compression) engines (not just QX and QD).

548937 was used the same way as the '936 above, except that it's for .0010 undersize.

Those descriptions are from the parts list at the end of the manual. If I'm reading things correctly, the guys on the engine assembly line were actually supposed to use some charts earlier in the manual to choose the proper bearing shell for each location. I'm not going to retype everything, but basically they made a measurement of the block's bearing bore and of the crank's journal diameter. Based on those measurements, a bearing shell was selected from the charts to produce the desired vertical diameter clearance.

This sounds like a lot of work, but the task was apparently broken down into multiple jobs. Each bore and journal was measured ahead of time and marked with a dab of colored paint. The guy installing bearings simply had to look at the two colors for each location, find that combination on the charts, then grab the proper bearing.

 

Wow. I had no idea that there was an engine assembly manual, or that bearing numbers were in it, or that they would be different from the bearing numbers in the parts manual.

At least my idea about the "0005" and the "001" markings was correct.

Is the engine assembly manual available on line, like the general assembly manual is, or does one have to buy it?

Thanks.

- Eric

 

Okay, having reviewed the regular Assembly Manual, I can see that in its index, it makes reference to the Engine Assembly Manual as a separate book (Section 6 of the Table of Contents).

Is this a readily available publication? Would it be possible for anyone to shoot me a scan of the relavent tables of specs and parts? It's mostly just for curiosity, but I'm always happier to have the manual than to speculate.

- Eric

 

Ding ding ding!!!
You're the first person I know to have figured that out himself.

Years ago I bought a copy of the "Engine Assembly Manual" at a swap meet, not knowing what it was. A little later I figured out that it was the document referenced in the table of contents of the whole-car assembly manual; it has the document number listed.

I also became aware that not many people had a copy of this manual, and it really is essential if you're into originality and own a 1970 Olds. So I started selling reproductions of the manual. e-mail me for more information if you're interested in getting a copy. Maybe in the future I'll get a scanned version available on-line.

As for the part numbers, it was (and still is) very common for GM to consolidate the plethora of original part numbers into a few common, supposedly equivalent, part numbers. So even if you look in a parts catalog that was published just a couple years after your car was built, it's not uncommon to find part numbers different than what was installed on the assembly line (per the assembly manual).

I always get a kick out of people who go to great lengths to load their car up with NOS parts, even though those NOS parts don't have the same apperance, same performance, or even same part number as the original part.