1950s Shimming rear main seal 1955 331 engine

[Bob Kielar]

After 50 miles my 1955 rebuilt 331 engine the rear main has started to leak. The mechanic has used three different seals to no avail. I have searched on the forum and there is threads that the use of shims have helped. My question is what material (brass?) and size (.05 .010 .015) thickness and do you put it on the top and bottom of the seal?

Thanks,
Bob Kielar

[Jay Friedman]

I suggest you get in touch with Art Gardner, who has successfully shimmed the rear main seal in a 331. 

[Caddy Wizard]

After 50 miles my 1955 rebuilt 331 engine the rear main has started to leak. The mechanic has used three different seals to no avail. I have searched on the forum and there is threads that the use of shims have helped. My question is what material (brass?) and size (.05 .010 .015) thickness and do you put it on the top and bottom of the seal?

Thanks,
Bob Kielar

I had a new neoprene seal start to leak after about 50 miles, despite very careful installation.  I saw on the Forum that some speculate that the groove is not always the same dimension, while the seal is a precision part, so in some instances one might need to shim the seal to get a good fit on the crank journal.

To shim the seal, I took some thin gasket paper (I think it was 0.016" thick) and cut 2 strips the width of the channel and almost the length of each seal half.  I slipped one in the block and slid the seal half in (the seal then is between the crank journal and the paper shim).  It should still slide in without binding and requiring much force to get it to go in.  Then I installed the shim and the other seal half in the lower cap and installed the cap.  I put just a tiny dab of silicone sealant on the ends of the seal halves where they mate to each other.  I also indexed the seal halves so that the parting line between the two seal halves doesn't coincide with the parting line of the lower cap to the block.

So far, it is sealing well.

[Bob Kielar]

Thank you Art. I think we will give it a try both shimming and offsetting the seal.

Regards,
Bob Kielar