VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 Oversized Rope Seal???

Checking to see if I'm getting correct info... During the rebuild process if the crankshaft is ground down 20 under is it possible to find a rear main rope seal that is 20 over stock to go along with the new 20 over bearing?

When installing a new rope seal you need to trim the ends. They do have extra material when you get them.

Unclear on the concept...? O.D. of the bearing remains the same...

( Thickness of the bearing "shell" is the only difference...)

Unless of course, your block crankshaft journals were also align bored...Then the O.D. will be larger...But, it would still be an insignificant amount in your case...

For over a year I dealt with a leaking rear seal on a 216 1948 block. I pulled the engine twice and used different techniques to seat the new rear seal. Each time I still had a leak after driving the car less than a mile. So I used the shim material used for shimming the rods or crank caps. I just cut a narrow shim the length of the rope and put it under the rope. I figured if the rope was a little more snug it would solve the problem. I did it only on the bottom rope since I gave up on pulling the engine again to do the top seal. The shim did not make any difference. But maybe it was the top rope seal that was leaking? I decided to walk away from the engine and have a 41 engine rebuilt professionally this last winter for my 1941 car. I have not gotten the engine back yet, but am hoping the rear seal will not be a problem. You could try putting a little gasket sealer on both sides of the shim so the oil would not leak between the block and shim? Good luck, Please keep us informed on what you decide to do and if it worked okay. Thanks, Mike

thanks for all the info guys, I think i'm getting incorrect info. thanks again

Hi Fleetboy
When the crankshaft journals of an engine are ground it is called undersizing. So the main bearings inserts or shells will be undersize or thicker. When this operation is done at a machine shop, the rear main seal journal on the crank usually is just polished and not ground unless it is in really bad shape. When a rubber rear main seal is used in an engine, the crankshaft seal journal can not be ground undersize as this will cause a lack of tension of the seal lip to the journal surface resulting in leakage. A standard rope seal will take up a small amount of undersizing done to the seal journal on the crankshaft as the rope is not just laid in the groove in the engine block and main bearing cap but formed or worked into the groove to approximate the size of the crankshaft seal journal. This is the process that is not done or is done incorrectly which causes most of the problems with rope seals. If the seal in installed to tight, the resulting friction will burn the seal face and cause leakage. If the seal is compacted or rolled to tightly into the groove, then there is not enough contact between the rope seal and the crankshaft resulting in leakage. Another factor that affects rear main seal performance is the proper operation in grinding the crank main journals. If the crankshaft is not correctly centered in the crankshaft grinder, the main bearing journals can be ground off center from the centerline of the crankshaft turning the rear main seal journal into an eccentric lobe with a high spot. If this happens no matter what seal you use will never cure the leak.
Rope seals come in many different sizes by width and height depending upon size of the rear main seal groove.
Hope this explain it.
If you need rear main seals or gaskets, check out our website www.marxparts.com
Regards
Bob@marxparts

A friend in Canada had a leaking rear seal on his 52 and an old time mechanic cured it by inserting a stiff wire behind the seal to increase the pressure on the seal to crankshaft. I believe this was only on the block side and the cap seal was replaced with new.