Rear main seal leak

[Rusty_OToole]

I have a 1942 Chev (with a replacement engine of about 1950). It has been off the road since about 1965. I notice when I start it up the rear main seal leaks  badly. I believe it has become dried out or shrunk due to lack of use. Is there anything I can do about this short of tearing down the motor and replacing the seal? Will it swell up and stop leaking or at least slow down if I start driving the car regularly?

[Spinneyhill]

According to this site, http://www.chevytrucks.org/tech/bobadler-1.htm

the original seal was a graphite impregnated asbestos rope. A later seal might be made of something else impregnated in graphite. There is no "modern" type replacement. Hemmings also have a discussion about it: https://www.hemmings.com/magazine/mus/2009/03/Rear-Main-Seal-Repair/1782923.html

 

Maybe it will swell up again, but graphite rings alarm bells for galvanic corrosion if it dries out. So if the engine has sat for 50 years and the seals have dried out, you might expect to drop the sump and have a look at the crankshaft where the seal rubs to make sure it is not rusty. If any moisture got in there, you might find a bit of rust. I guess a reasonable wait to see if it stops leaking and if not, look and see!

[F&J]

19 hours ago, Rusty_OToole said:

main seal leaks  badly.

 

19 hours ago, Rusty_OToole said:

has been off the road since about 1965.

 

17 hours ago, Spinneyhill said:

If any moisture got in there, you might find a bit of rust.

 

 

I agree with Spinneyhill.    It may be not that common, but well known to vintage engine shops, that a 50-year dormant engine can have rust on the crank there, as well as the main/rod journals from acids trapped in the oil.

 

My 55 Olds totally remachined engine was only used a very short time before 40+ years storage.  I was cleaning the engine before install and decided to replace the rope seal.  I dropped the main cap and found what he said, as well as on the bearing journal!  Dropped a few rod caps and saw the same rust.  I had test driven this engine before taking it out to clean it, and there was a serious "pile" of bearing babbit micro-flakes in the sump.   That engine sounded fine, but never would have gone very far under a load.

 

Being you said leaks "badly" sends out a possible warning sign?  However, I also can't see it getting better if it is now "pouring out", even if the crank is clean.

[Doug Novak]

I had my Rear Rope Seal replaced in my '68 AMX V8 a few years ago by a local garage that does Antique and Muscle Car Repairs and Restorations. The recommended way to do the Rear Rope Seal replacement on mine was to go in from the top, which makes it easier to do. The shop pulled the engine, did the Rear Seal replacement and while in there they were able to replace worn Main Bearings, Gaskets and Seals. Everything else looked good.  It was a little costly but having it all done at the same time is cheaper in the long run.   Hasn't leaked since.  One other thing I heard was the newer thinner weight oil's especially Synthetic Oils can penetrate the rope seals causing them to leak.

[Dave Henderson]

The graphite impregnated rope seals used on main bearings could sometimes be replaced without having to do a lot of dismantling work, just the pan had to be pulled.  The main bearing bolts were loosened a bit and the cap of the rear main was removed.  A screw such as a drywall screw was screwed into the end of the upper seal and it was pulled on it while gently pushing on the other end with some appropriate object, and with luck it would come out.  Inserting a new top rope could be accomplished, at least in the good old days, when a wire "chinese finger" tool could be obtained that would be shoved up and around the crankshaft.  Once the finger end passed through, the new rope seal 's end was inserted into it, and by pulling on the other end of the finger device the new seal was grasped and could be gotten around the upper part of the crankshaft journal.  The exposed ends were then trimmed. The main cap  got its new rope seal and it was rolled upon to seat it, and then its ends were trimmed. The rear cap was installed, the mains were torqued back up, the pan installed, and you were about done. 
The tricky part may be finding the finger tool, I dunno, they may still be around.