VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 1931 engine bearing shim adjust

Greetings,
I am looking for help with the bearing adjustment on my 31 coupe.
Engine has bad knock.
Is there a thread on the site or on Bill Barkers site, or you tube?
Thanks for any help,
Three Window
Randy

Use a Repair Manual and follow the instructions on adjusting the rod and main bearings. Those engines are intended to be repaired under the old Maple tree in the backyard. A reprint manual is available from The Filling Station or many other literature dealers.

I had a problem with some engine knocks when I rebuilt the '28 engine that is in Lurch back in 2017. The babbitt bearings that you have in your '31 are similar and I suspect the troubleshooting would be similar too.

I documented my rebuild in the VCCA 1912-1928 category. Note: I did an inexpensive rebuild, so I did not have new babbitt bearings pored. When (and if) this engine gets rebuilt in the future, it will need new bearings pored and line bored.

Here's a link to where I dealt with the engine knocks: https://vccachat.org/ubbthreads.php/topics/404082/re-resurrecting-a-28-4-banger.html#Post404082

Hope this helps. Dean

Thanks Chipper and Rustoholic,

Im using plastaguage among other methods.
What is the minimum clearance for oil lube.
I think Ive seen 15 thou speked.

Thank again.

Interested in your trailer build.
Any more pics avalible?

Hi Randy

Outside of getting someone who has done this before to help you,
as Chipper said, your best bet is to consult an actual Chevrolet repair manual.

Oil clearance for your engine is more of a "feel" thing than a "measured" thing.
This is probably due to the babbit used in the bearings.

Plastigauge will be good for determining the clearance you have now, but not for final fitting.

If the final setting WERE to be accurately measured, the MINIMUM would be not much over .000",
or in other words... a light drag, so the rod can be tapped from side to side with a small ball peen hammer.

The MAXIMUM would be not much over .001",
the amount you get when you add a .002" shim to ONE side of the rod.

At any rate, you do NOT want "15 thou"!! 🙂

I agree that the adjustment is as much or more a "feel" scenario as a measured one. A limitation with Plastigage is that you have to "force" the clearance to the portion of the bearing where you insert the Plastigage. This takes a little extra care especially if you are using it with the engine in the vehicle.

On the rods, this means that you need to have a way to pull the rod down so the top of the bearing is tight against the journal.

When checking the main bearings you have to push the crank up into the block. The "push" needs to be applied as close as possible to the main that you are checking. Othewise the flex in the crank will produce a false reading.

I think you meant .0015 or "one and a half thousandths".

If the engine has a bad knock it is probably going to takw morw than adujsting.
Inspect te condition of the babbitt on both the rod and cap first.

Agreed

Even if the babbit and journal are still okay, there probably aren't enough shims left to fix a "knock".
Especially if it's been there for a while.

Although it is "not recommended practice" many backyard mechanics placed shim stock under the main bearing shells. It would be used in an instance where an entire rebuild is delayed to an otherwise okay engine. I have torn down engines of this vintage and discovered shim stock under the bearing shells. I have my step grandads shim stock package that has .002", .003", .005", .010", and .020" rolled up all in one canister. He could put together about any combination of thickness needed.

Art