14. Oil leaking from the bottom of the flywheel cover

There are only three sources for a continuing oil leak appearing below the flywheel housing: (listed somewhat in order of likelihood)

1) Overfilling the crank case. There is no conventional seal in front of the crankshaft, and if the crankcase is overfilled by much more than a quart or so, some oil can splash out of the front of the engine, just behind the flywheel, especially when sailing in choppy water.

2) A leaky gasket between the flywheel housing and the front of the block. Such a leak would be very unusual except possibly immediately after an overhaul.

3) Clogged drain holes in the "slinger seal" in front of the crankshaft.

The slinger seal consists of a collar machined around the front of the crankshaft where it extends out through the flywheel housing, just behind the flywheel. The outside edge of this collar is sharpened to a dull edge which lines up with the inside diameter of the hole in the flywheel housing. When oil tries to leave the crankcase, it encounters the crankcase side of this collar, and gets "slung" outward (hence the the name "slinger seal") into a groove cut into the inside diameter of the hole in the flywheel housing.

There are small drain holes (approximately 5) in the bottom of the groove around the inside of the hole in the flywheel housing, which allows the oil to flow back into the crankcase after it is flung outward into the groove by the edge of the sharpened collar on the crankshaft.

Every now and then, those holes get clogged with crud and oil cannot flow back into the crankcase as fast as it is being flung out by the slinging collar. - Updated: November 4, 2003