Back to Andy's question this seal should not be used in engines made prior to 1956...and around 2002 a tech engineer at Fel-Pro told me it was actually made of Viton. He said the neoprene idea came from a misunderstanding. There were machining differences that were corrected in the 1956 engine (which as I recall is when this seal was introduced). They're ok for the 56 through 62, however. Having said that I helped a friend use one in a 1955 engine a long time ago but we ended up having to shim the bottom half of the gasket to make it work.
I have the Fel-Pro orange seal in my 235 (a 1959) and I had to shim it also. In addition to shimming, I had to use a Dremel tool to grind a wee bit off of the steel inner rod of it (to eliminate interference there). Also always polish that part of the crank as much as possible. Just like the harmonic balancer shaft, any roughness or groove or irregularity will wreck the seal quickly. The surface left by the rope seal is anything but smooth...some of them are pretty rough and pitted. I have read the Best Gasket seal won't last and some believe it is made from a different material...not Viton. But I'm not sold on Best Gasket products as some people seem to be.
As for how mine is holding up, it did perfectly for 2.5 years and now it will allow a bit of oil through...especially if I use 10-30 oil in the summer. A bit defined as one drop or two per week. Just enough to irritate me. I've decided that's about the best you can hope for with that type of seal, however. One other big concern (aside from polishing) is the clearance between crank and bearing. .001" to .0015" is ideal. The wider that gap gets, more oil flows out of the bearing and the more your crank moves around. A spring loaded lip seal will compensate for that, but this seal can't compensate as well. I've always thought a slinger might help direct oil away, but have never tried this. The very best would be the one-piece seal.
Back to the Fel-Pro Viton seal, here is what I would suggest: use a micrometer or at least a 4 place digital measuring tool to measure the diameter of your crank surface (after it has been polished). Then set the two halves of the seal on a flat surface, force them together (top and sides at the same time) and measure the interior diameter you have. You'll have to get your wife, girlfriend or a helper to assist. If the interior measurement of the two gaskets isn't smaller than your crank diameter, it won't seal right. It needs to be .006 to .008" smaller in my experience. Good luck.
Last edited by Jon G; 10/23/2021 5:12 PM. Reason: typo
