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

[Mike K]

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[hrpearce]

Thank you Mike much appreciated.

[Alex van de Wetering]

Thanks everyone for all the replies, info and suggestions.

David; thanks for checking the manual. Interesting to see that GM 608421 is advertised by a parts supplier as being 010 oversize; if it proves to be Standard in stead, than maybe this is the solution for Maurice!

Thanks Maurice; I am after a full set of (preferebly precision) main bearings size 030.

Mike; Thanks for uploading the booklet; very interesting!

Phil; I am a regular on your website; so much interesting info...and I still have a lot to learn when it comes to the mechanical side of our beloved CMP's!

Keep us posted on your progress.

Indeed, it's about time I update my resto-log. My focus is on the engine and rear axle for this winter, as I hope to have the truck running, nex year!

Alex

[Alex van de Wetering]

David; thanks for checking the manual. Interesting to see that GM 608421 is advertised by a parts supplier as being 010 oversize; if it proves to be Standard in stead, than maybe this is the solution for Maurice!

608421 Consists of (1) 603943 Front Bearing Unit, (1) 603944 Front Inter.Bearing Unit, (1) 603946 Rear Inter. Bearing Unit, (1) 604359 Rear Bearing Unit, (2) 839125 Dowel Pin.

hmm....Even though the Canadian C8 parts list does not list the set "608421", it does list the individual bearings "603944, 603946 and 604359"....but all marked "for line reaming". The front crankshaft "for line reaming" bearing is listed as "604943"....a typo in the manual maybe?

Alex

[motto]

Alex
I have checked the TM and can confirm that all part numbers I have transcribed are as they appear in the manual.
This may indicate that one or other of the manuals is incorrect, but which one?
Somewhere there must exist a compilation of all bearing part numbers and their applications. All we seem to have are fragments of information that do not neatly dovetail.

David

[Mike K]

I have sets of precision main bearings NASCO brand . But not 100% sure if they fit the 216 .They appear to be the correct size for a 216 . both 20 and 30 under . I found them in Uptons shed at Corowa , must be 20 sets .

I posted a query on the GMH facebook page with pics of the bearings.

[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.

[Mike K]

Originally Posted by Mike Kelly

I have sets of precision main bearings NASCO brand . But not 100% sure if they fit the 216 .They appear to be the correct size for a 216 . both 20 and 30 under . I found them in Uptons shed at Corowa , must be 20 sets .

I posted a query on the GMH facebook page with pics of the bearings.

I have measured these NASCO bearings and they do measure up as 216 main bearings . I've got a feeling these are rejects or 2nd grade , they are oval shaped , maybe this is normal. They squeeze down to a round shape when the caps are tightened down ? They might be useless