Rear main seal Again


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By paul2748 - 11 Years Ago
About two years ago I replaced the rear main seal with a neoprene one as part of a restoration of my 56 Bird (312).  Last year I went on a trip across country (6300 miles) and the seal started leaking, so last winter I replaced it.  I just came back from a 2200 mile trip and the new seal is leaking.  This latest seal was one by Best recommended by Ted. I bought it from John.  I also installed an aftermarket retainer (when the seal was replaced the first time) and everything was checked for trueness (replacement was done out of the car, crank removed) when the second seal was installed. The crank surface was smoothed as part of the seal replacement.

The first time I replaced the seal the engine had a rope seal that really wasn't too bad. I am thinking of going back to a rope seal.  A while back , Best gasket came out with a graphite composition that is supposed to be much better than currently available rope seals..  Has anybody used one of these? Any luck with it?

As part of this is crankcase venting.  I currently use the old vent tube.  Is going to one of the PCV kits a better choice as far as real main problems go (internal pressure)?

Thanks for any information.
By slick56 - 11 Years Ago

Paul, i would try the PCV conversion before i replace the rear main seal,
it really does help lower crankcase pressure.
By Ted - 11 Years Ago

Paul. Was that last installed neoprene rear main seal orange or black?  The orange seals have been lasting about 2000 miles but I’ve had no problems yet with the latest Best Gasket 312 neoprene seal offering which is black.  If you have the latest black seal in place now, then this will take a much closer examination to determine exactly what is going on.  As slick56 mentions, a PCV valve may help if the leak is minor.
By Jeff - 11 Years Ago
I replaced the original rope seal on my '56 292 with the neoprene seal.  Now this is a 60,000 mile original engine that's never been apart (except for my messing around).  The leak stopped for a while and then returned.  I assumed that the condition of the journal was effecting the neoprene seal (it has some corrosion, etc).  I had cleaned up the journal as best I could before installation.  Given the condition of the journal I decided to try the Best Gasket graphite rope seal.  This is all being done with the engine in the car so it wasn't much fun.
Using one of those Sneaky Pete installation tools (Chinese finger puzzle) we managed to get the seal installed.  It took one person pulling like crazy on the tool and the other pushing and guiding the rope.
We determined that to get the tool and seal to fit over the top we tapered the end of the seal and fit it into the very end of the installation tool. Just as the seal was around the crank the tool slipped off the seal, but it look like we were just passed the portion where we had cut our taper.  So I decided to button it up and hope for the best.  At first I had a small leak but after some driving I think I'm happy with the results.  The graphite seal material is pretty cool and nothing like the old rope seals.
Hope this helps.
By paul2748 - 11 Years Ago
Both seals were black, not sure of the manufacturer of the first one.  I don't consider the leak minor as I'm going through a quart every 450 miles or so (traveling at 65 MPH).
By charliemccraney - 11 Years Ago
Are you positive it is not coming from another place on the engine?
By paul2748 - 11 Years Ago
I'm going to check this out in the next day or two.
By hotdoger1 - 11 Years Ago
I put in black seal from napa ten years ago. today I still get 1/2 quart to 2000 miles. I have a blockoff plate on the side of engine pcv  valve piped from the back of lifter cover into the bottom of  air cleaner.
By Ted - 11 Years Ago

You'll have to take into account that Paul’s engine is a 312 which has a completely different rear crankshaft seal than that which is required for a 292.  312’s have larger main bearing sizes which also requires a larger diameter rear seal.  While neoprene rear seals have been available for the 272/292 engines since the early Sixties, it wasn’t until about eight years ago that a commercially available orange ‘rubber’ seal was made available for the 312 engines by Best Gasket.  That orange seal proved to be too soft and wore out quite quickly.  About two years ago, Best Gasket redesigned the 312 seal so that it was a firmer material and similar in texture to the black seals already available from several different manufacturers for the 292 engines; this new seal replaced that troublesome orange seal.  On my end, the latest Best Gasket 312 black seal offering has been holding up. FordCraft has for a number of years offered a modified Chrysler neoprene seal that also works in the 312 engines and I’ve used those with success also.  I’ll also add that PCV valve systems are used on almost all the Y engines I put together and that has to help in reducing the potential for oil leaks from these engines.