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1929 Pontiac oil leak

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I am having the engine rebuilt in my 1929 Pontiac by the local machine shop. Everything has went pretty smoothly except they have an oil leak they are not for sure on how to fix. They have the engine running and probably have about 2 hours run time on it so far. There is an oil leak between the rear of the crank and the block. There originally is no gasket there. They say it is made to drain the oil from that area back down into the pan. We assume they always have leaked some because of the design but they are not comfortable letting it leave because of the size of the leak. Concerns with getting oil on the clutch etc. Does anyone have any suggestions on a fix?? Thank You for your help!

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Did they insert the proper wooden seals on each side of the rear main cap?  If the rear main clearance is correct and the wood seals are in place the groove at the rear of the engine should carry the oil down to the drain hole and into the crankcase.  By the way EGGE has the wooden seals.

Are they running the engine on a stand?  If so that may be their problem because there is no suction through the crankcase and it builds up pressure.  When driving on the road the road draft tube alleviates this situation.  At an idle the air from the fan blowing into the oil filler tube is sufficient..

Did they use new pistons with all the rings above the wrist pin or reuse the originals with one ring at the bottom of the piston.  If so maybe they didn't notice that the bottom ring comes half out of the cylinder at the bottom of the stroke.  If a three piece oil ring is used here (rather than the original type) the first time the engine turns over you break the bottoms off all the pistons.

Edited by Tinindian (see edit history)

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My parts book shows 2 wooden wedge blocks in both the front and rear main bearings.  I do have some of these blocks NOS @ $4 each.  Call me if you want to order them.  Kurt 641-648-9086 Thanks

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Well the machine shop installed the wooden seals and it did not stop the leak. Of course I know it is next to impossible to diagnose an engine leak when you cannot see the engine but does anyone have any other ideas??

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