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

[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]

Relining steel bearing shells with new babbit, it is possible to achieve good results with basic equipment . Some of the vintage car people with rare cars ( replacement parts not available ) have successfully relined steel bearing shells with new babbit in a home workshop . You need to find the correct flux and some new babbit . I'm not saying its a quick and easy job but the other option is to pay somebody 300-400 bucks per shell.

With babbit rods, if you have a lathe with decent throw, after the babbit reline you can bore the rods to size. Make a mistake, no problem , go back to the beginning and melt out the babbit . Try again .

Years ago at the Melbourne Showgrounds swap, they had a line boring demo setup, an old chap had the block set up and the cutters slowly went through each bearing .

[Alex van de Wetering]

Thanks guys; your reactions are very much appreciated!

David; I agree....there must be a typo in one of the manuals, as the other 3 bearing numbers do match. They were thorough though as the index shows the same number.

Lynn; thanks for the explanation on the different bearings. At first I thought the quality of the wartime blocks was rather poor which meant line-boring or hand scraping was always necessary....which is why I couldn't figure out why "precision" bearings would also work. Silly me! . That was before I noticed the line-boring type bearings only come in one size....and "hand sraping" and "precision" bearings in several oversizes.

I now understand the benefit of the line-boring type bearings (at the time)....from what I have heard there is a lot of "meat" on these bearings, which means the supply line would only have to provide one set of bearings which could than be line-bored to the neccessary oversize.....in stead of supplying several bearings sets in several oversizes. But, of course the downside is extra labour and equipment to do the line-boring.

The problem I have found so far in finding bearings for my Chev is that a lot of the Ebay adds have incomplete or incorrect decriptions....often it's not clear what type of bearings is being offered (line boring, precision etc.) or sets are mismatched or incomplete. One set currently being offered as STD bearings display the same numbers that David posted earlier...which according to the Canadian manual would make them the lineboring type!
Same with a dealer in France.....a set marked "010" again uses the same numbers, which would again make them the "lineboring" type.....which nowadays seems to be a rather expensive procedure at the engine rebuilders.


Mike; Yes, I did read about some tractor restorers here in Holland that do re-babbiting themselves...however I wonder how these bearings would hold up? Maybe for a tractor it would be good enough....but for a fire-breathing CMP?

Alex

[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

[Lynn Eades]

Alex, I'd suggest locating some post war (commercial branded as opposed to NOS military) this should come up with steel backed precision bearings. (std from 48 on)
It is probably worth the extra money for a recently made set, from a reputable manufacturer.

[Alex van de Wetering]

they are oval shaped

Mike; do you mean the radius of the bearings is bigger than the radius of the caps? I guess that's a good thing....as it clamps itself inside the cap, rather than around the crank, right? (wishfull thinking maybe )

Did you use the NASCO bearings for your C8 at the time?

Lynn; thanks again for your ideas. Maybe, getting a proper newly made bearing kit is indeed the way to go, but I have some leads, one of them a very good offer from Mike, so I want to see if this could be the solution for my engine.
But I agree...with so many wrong descriptions of NOS bearings sets around, it could be wise to spend some extra cash on a set from one of the Chev parts dealers in the US instead.

Talking about oval shaped bearings......Do two bearings shells clamped together by the caps from a perfect circle?......or an oval, with shims needing to be added to get the result to be a perfect circle?

Alex

[Lynn Eades]

Alex, I am not 100 % sure about the shims, but logic says they are left out with the precision bearings.
These bearings are made to fit a given size bore (tunnel) a part result of the factory line boring of the block when machined.
The precision bearings when paired do not form a perfect circle in this situation as they are usually "sprung" to some degree.(Is this what you have Mike?) This helps them hold in place during assembly (before the caps go on) I think this is the "nip" part of the motor reconditioner's term "nip and crush"?

These bearings also have "crush" Basically when the cap is pulled (torqued) down, the ends of the bearings at the split line are crushed together, forcing the shells into a tight fit with the tunnel bore. This is important as it stops the bearing from rotating in the bore, and it achieves a metal to metal surface contact, essential for heat transfer.
To follow on, the block bores and the shell backs should be cleaned with a solvent and only fitted when perfectly clean and dry.
BTW. the locating tab would not stop the bearing spinning and in modern engines the manufacturers don't use them.

[Mike K]

Originally Posted by Alex van de Wetering

Mike; do you mean the radius of the bearings is bigger than the radius of the caps? I guess that's a good thing....as it clamps itself inside the cap, rather than around the crank, right? (wishfull thinking maybe )

Did you use the NASCO bearings for your C8 at the time?

Lynn; thanks again for your ideas. Maybe, getting a proper newly made bearing kit is indeed the way to go, but I have some leads, one of them a very good offer from Mike, so I want to see if this could be the solution for my engine.
But I agree...with so many wrong descriptions of NOS bearings sets around, it could be wise to spend some extra cash on a set from one of the Chev parts dealers in the US instead.

Talking about oval shaped bearings......Do two bearings shells clamped together by the caps from a perfect circle?......or an oval, with shims needing to be added to get the result to be a perfect circle?

Alex

My C8 has the original babbit lined rod bearings, I removed a few shims from each cap and it's been fine. I polished the journals before re-assembly with a fine emery cloth .

A good engine machinist will fit the new bearings in the caps , then he bolts the bearing caps down and tightens to the torque specification ( no crankshaft in place ) , then he measures the bore of the bearing with a accurate gauge . The measurement tells him what size to grind the crank to , normally they allow about .001"per inch of diameter for clearance . eg for a 3"diameter journal, they aim for a .003"clearance

Measuring the bearing bores after the caps have been tightened down ( no crankshaft in ) is very important . I think a slight oval is acceptable.

I think Lynn explained the crush concept well. Anyway I hope the NASCO bearings fit .

[Maurice Donckers]

Alex , I found several sets 0.30 , and 0.40 in my stock .