Chevrolet 216 235 (early) main bearings? The same?

[Lynn Eades]

Hi Alex.
I cannot confirm they are the same engine, or if they use the same bearings.
However, I can confirm that that the main bearing journals for the Chevy Cargo G 506, are he same diameters as Chev. cars from 1939 to 1951.

A "Motors Auto Repair Manual" describes The main bearings as "35 to 47 engines are Babbitt lined steel half shells. For replacement however, precision type bearings are furnished. These precision brgs. are of the same design as are used as standard for 1948 and later engines."

Your Question about "hand reaming" and "precision" bearings may be clarified a little by this: (my words)
The G506 book (TM 10-1557) explains a procedure where bearings are fitted and reamed to a finished size with a hand operated boring bar (which is first centered in the bell housing (clutch housing) gearbox pilot hole + front jig)
This operation could I guess, be carried out in the field.

I have heard of bearings being called "pre finished" (where they are made to first fit and then the Motor machinist line bores them to size)
What they mean by "precision" bearings, is a bearing shell that you just install because it is already finished to fit.

TM 10-1557 describes the main bearings : "Chevrolet main bearings are steel back babbitt- lined. The Babbitt is centrifugally cast or "spun in" into the steel lining. This method assures a positive bond" It continues.

Essentially the difference is Babbitt is very soft, will tolerate larger clearances and is somewhat forgiving. They can be adjusted (shims removed) The Babbitt is thick and by comparison The thin bearing material of a precision bearing (shell) when damaged, becomes junk.
The difference between the G506 motor (July 42) and the 50-51 car engine seems to be a very minimal difference in compression ratio. This may not sound much, but the crankshaft might be quite different. (counter weights?)
As Phil said, there is the pistons to consider, and there might be valve timing?
I don't know much about Chevs and the TMs don't give history or model comparisons.
I hope that's some help.