346 Flathead Oil Leak

[KenZ]

Within the last year I replaced the original 346 engine in my 1936 Cadillac with a WWII tank engine.  The engine runs and sounds great with 25 â€" 30 oil pressure.  The final challenge has been to fix an oil leak.  The leak seems to be most prevalent in the rear valley cover area (underneath the intake manifold) where the flange mates to the block.  I have removed, and replaced the gasket applying sealant without fixing the leak.  The valley cover itself was in good shape with no cracks or uneven surfaces.  I removed inspected the distributor tower shaft per another forum topic.  I also inspected the breather system for any obstructions.  The leak only occurs after the engine has been sitting for few hours after operation. It does not have any noticeable leaks in the subject area while the engine is operating.  I am suspecting that oil is accumulating in the rear area of the engine valley after operation.  Any ideas or similar experiences out there?  Thanks,  KenZ

[Bobby B]

Ken,
Hi..Is it leaking between the valley covers and the block OR from where the crossover breather bolts go thru each breather to secure it to the front/rear valley covers, therefore pooling down the valley cover and sitting on the flat surface the block, giving it the impression that it's coming from the valley cover to block gasket? Did you put the felt "O-rings" around the breather openings before you bolted it down to the valley covers? Oil should NOT pool in that area at all. Due to gravity, no oil should be stuck to the underside of the valley covers. Do you have a clog/ excessive blow-by? If you can't pinpoint it, get new gaskets and put a light coat of "The Right Stuff" by Permatex and torque your valley cover bolts down evenly. Then if you want to, you could put a coat of grease on the felt washers before you bolt them through the valley covers to hold your crossover bar down. You shouldn't have any leaks going on there unless there's a tear in the valley cover gasket or it's been over-torqued and squishing the gasket too much and distorting it. Not much pressure needed to seal those valley covers.
                                      Bobby

[Bill Ingler #7799]

Ken: You might check to see if you have a good gasket under the distributor tower as shown below. My 41 engine was leaking oil and I finally found that someone had not put in the gasket at the bottom of the distributor tower.   Bill

[Steve Passmore]

All good advice so far especially about the felt seals under the vent tubes and not over tightening the valley cover bolts, the cork will split very easily.  Why it only leaks when you stop is confusing though.
The factory also fitted copper washers under the valley bolts. I have found them left off many times. Could it be leaking around the bolts?

[Bobby B]

All Good Points...
              Bobby

[KenZ]

All good ideas and I have verified pretty much everything mentioned in the above responses.  I am under the same impression as Bobby regarding oil pooling in this area since after operation the oil should migrate downward.  The distributor tower shaft has a new thin gasket with sealant.  The felt breather gaskets are dry and breather system seems unobstructed. The bolts all have the tiny copper washers.  So I guess its back to changing the cork gasket again and try the "Right Stuff".  The leak isn't terrible just annoying. Thanks to all for responses.  Ken     

[Paul Phillips]

Seems strange to be leaking only after running and not during operation.  The breather crossover is the only thing that would feed that area by gravity.  Otherwise, the two things not mentioned to check would be the oil inlet fitting in the middle under the intake and the oil pressure gauge fitting.

Paul

[Bobby B]

Seems strange to be leaking only after running and not during operation.  The breather crossover is the only thing that would feed that area by gravity.  Otherwise, the two things not mentioned to check would be the oil inlet fitting in the middle under the intake and the oil pressure gauge fitting.
Paul

Paul,
Good Point....Those 90 degree brass fittings can crack, and the oil fitting is a funky thread. If it's the original gauge, the tubing might have a hairline crack where it's soldered into the fitting, therefore causing the hot oil to return back from the gauge, thru the line, and possibly out of a hairline crack after the engine is shut down. The super thin gauge tubing is way fragile.....
                                                                                                                                                                                Bobby