Re: Leaking Rear Main Seal

Posted by marith mccoul on Oct. 17, 1996 at 12:36:24

In Reply to: Leaking Rear Main Seal
posted by Asa Scranton on Oct. 10, 1996 at 17:05:34

In original Model A's, Henry designed the rear main with a "trough" in which a "slinger" built on the crankshaft ran.The idea was that excess oil from the rear main would find its way through the bearing and out the back, oiling the full surface of the bearing as it went.He put in a little groove running toward the front to help spread that oil around, but the bulk of the oil would come in from the top, through a passage from the valve chamber, and circulate, finally finding its way out the back where it encountered slinger and trough.The trough had a hole in it that led through the bottom main cap casting and out a "rear main drain tube".In 1930, it had become clear that this drain restricted the oil enough that too much was finding its way out the back, so a larger tube was installed.When an entirely unacceptable amount of oil leaves the rear main, it may be several things:1-maybe you just need to upgrade to the later, larger drain tube.2:Maybe you need to take out a shim or two - check the clearances on your main caps.They should be .001 to .002.While you're there, check the clearance between the thrust face of the rear main cap and the crankshaft.It should be .004 to .007.This last item is one that can only be correctly repaired by re-babbitting, if it's found to be out of tolerance, however I have heard of people building the thrust face up VERY CAREFULLY with solder.3.Your drain tube and/or return passage aren't plugged are they?4."Entirely too much oil" on the driveway is a relative thing.They'll always drip a little.Or is this a "texas oil strike"? Some people, faced with out-of-tolerance mains have been known to partially plug the hole in the valve chamber to slow down the rate of oil feed to the rear main and thus the leak.I don't recommend it.Sitting doesn't hurt babbitt and there aren't any seals to dry out.Either the restorer did the job right, and something's plugged, or he did the job wrong and you need to fix it, or he didn't do the job at all.Skipping the rebabbitt job on the mains is a real common "shortcut" 'cause it's difficult and expensive.

Follow Ups:
Re: Leaking Rear Main Seal Asa Scranton Oct. 24, 1996 at 09:23:55(0)

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