The Stovebolt Site Forums The Shop Area Engine Shop Leaking rear main seal (oil) - Now You See It, Now You Don't

This 1951 216 has had a rear main seal leak since I brought it back to life in 2021 or so. It leaked/leaks a prodigious amount of oil when parked (and probably when driving, too).

It has leaked enough oil where I have to add some every couple hundred miles or so. In other words, I carry oil with me and I check and add frequently.

Lately, the oil puddles have diminished in both the amount of oil and in frequency. Sometimes, after parking for a short period of time there is no oil or very little oil on the concrete whereas before there was a large slick that needed immediate application of kitty litter.

I've put about 5000 miles on the truck since I got it running and driving.

As much as I'd like to believe that some problems fix themselves, I realize that that is not the case. What do you think is the cause behind a leaking rear main seal suddenly leaking considerably less oil?

Oil has been 20W-50 the whole time. I would have thought if the rope seal were going to swell up and re-seal itself after a long rest, it would have done so early on in the engine's re-awakening.

Any thoughts?


And yes, I'm aware of the old adage about Harley-Davidsons and all British cars. It does have oil in it up to the full mark on the dipstick.

If it's a daily driver, it probably won't leak a lot. Sitting for extended periods between trips probably lets the seal dry out and shrink, and it has to swell up and tighten onto the crankshaft hub when you start driving again. There are quite a few OEM rope seals on Ebay, the kind with that "unmentionable" material in them that actually makes the seal work right!
Jerry

That's what I first thought but would it have taken 5000 miles and 2+ years to swell up?

Do you think the July to January "rest" it had while it was at my mom's and the subsequent down time due to the bad gas/faulty gas tank episode played a part? It was already leaking a lot prior to that period of time and was still leaking after it got back into regular use but then, almost suddenly stopped leaking profusely.

Whatever the reason, I'm not complaining.

I found several of these seals on Ebay, at MUCH better prices that what's listed here. Bought a bunch of them! Machining the back of the block with a cylinder boring bar is simple and accurate, but it requires a teardown to the bare bones to do it. It solves the leak problem permanently, and also allows the use of a speedy-sleeve on a crankshaft with a worn seal surface.

www.motion.com/products/sku/01315653

Jerry