The Stovebolt Site Forums The Shop Area Engine Shop (1953-62) Neoprene Rear Main Seal-235 CI

Has anyone used one of these Neoprene Rear Main Seal-235? Our discussions have led me to believe today's rope seals aren't what they used to be. I'm just curious if anyone has used one and how it's holding up.

There's also the option of machining for a one-piece lip seal; however, this two-piece seal would eliminate the cost of machining. I've got a 1957 235 candidate for some new seals and gaskets and I'm trying to decide how to approach this, thanks.

Rear main seals have been beaten to death here . . (a poor joke).

The Best Gasket 6100 Rear Main Seal is good , but, their rubber rear main seal might now be good.
Wait to see if anyone has used their 4519S Rubber Rear Main Seal.
Maybe someone will post a link to the correct installation procedure for this seal?

Here is one procedure for the 6100 seal.

Just a note about Best Gasket and their products and, more importantly, their customer service.

The Best Gasket neoprene rear main seal for Cadillac 390/429 engines leaks within 30 minutes of installation. This has been verified by many people in the Cadillac community. Best Gasket's response to numerous complaints is/has been to ignore them rather than attempt to re-design the gasket or even figure out the exact reason for the failures.

Recently, a friend replaced the seal in his car twice with the Best Gasket seal, both of which failed almost immediately. After discovering that this problem was common to others with the same engine using the Best Gasket rear seal, he sought out NOS Felpro gaskets.

Needless to say they fit perfectly and didn't leak.

I wouldn't use the Best Gasket unless you have a long list of people who have installed it on the same engine as yours and will verify that it works as it should.

Not trying to pile on here but, the Willys Jeep 134 engine has the same problem with the Best Gasket rear main seal leaking, they are made to big. One builder of the Jeep engines is now having his cranks welded oversize and ground to match the spec of the Best seal since the NOS supply has dried up.

Mike B

I found the Jeep F head engine in my ‘61, unreliable, rings wore fast, etc., replaced it with GM 4cyl. from Chevy II, no more problems.

Ed

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.

Jon. here's work-around to avoid modifying the seal. A 3 7/8" Speedy-Sleeve on the crankshaft hub will increase its diameter around .010" and help the seal do its job. It will also restore the surface with super smooth stainless steel for the best sealing.
Jerry

Jerry, I'm glad you mentioned that. I bought one of those, but when I set it on the table and placed the 2 sides of the Viton seal around the outer edge, it seemed like there was going to be about 1/16" gap on each end. Doesn't that seem too tight to you for that sort of seal? I can see it working fine with the one piece seal, but I sort of wondered about the 2 part type. The sleeve I have is 3 7/8" id and as I recall the wall thickness of it was something like .012". I recall there were 2 sleeves that could have possibly been used on a 3.875" shaft. On one, 3.875" was in the middle of two measurements and on the other the 3.874" was the max diameter shaft that sleeve could fit on, so I figured it might be possible. Ideas?

Use the smaller diameter sleeve and secure it with red or green Loctite to assure that it doesn't spin on the shaft. If I can get away from this oxygen hose eventually, I've got a lot of work in progress, including fitting a speedy sleeve to a stovebolt shaft that is in line for some custom grinding. It's headed for my Frankenstein 235 that's going to end up close to 270 cubic inches.
Jerry
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JonG, you are absolutly correct. The neoprene/Viton seal was introduced for the 56 model year and its introduction is announced in the 56 pass car shop manual. So you would see that seal in 235s with casting dates consistant with the 56 production run. I have a september 55 motor that came with the neoprene seal and the 848 head with makes sense as the assembly plants were shut down September 56 for retooling and the casting dates on motors were generally a week or so ahead of an assembly date. That being said, I am still not 100 percent sure whether the truck line, or some of it, got the seal for 56. The problem being is that I have never had an unmolested never taken apart truck 235 or 261 in my hands. Being the work horses that they were and are, those motors often had an in chassis ring job, valve job, rear main seal replacement. The trucks needed to work so no time to waste.

The 55 motors on the other hand were still using shims, the rope seal and if stick shift, most still used the milk bottle lifters and the shorter push rods. The issue with the 55 rear main cap is that it was never designed for, and thus, never machined for, the hard seal. It was instead machined deeper which is why installing the neoprene seal in a 55 and earlier motor generally does not work and/or requires shimming, and even then, it still may not work.

My thanks to all of you that responded to this thread. I for one, learned quite a bit about the proper application of these rear main seals!

Jon, try fitting that seal around the crankshaft flange without a speedy sleeve. I think you'll find that it has an end gap that way, also.
Jerry

FYI-Last week I made a call to Best Gasket and asked them if any sealer is applied to the ends of the two-piece seal. The person I spoke with said no sealer such as Black Ultra RTV is recommended. He went on to tell me the seal should be installed with the two joints offset from the oil pan/block mating surface. IIRC, he said the installation instructions are on the packaging the seal comes in and the lip of the seal goes toward the front of the engine.

Thanks again everyone!

I've done that, Jerry. I have 2 cranks...one a 1959 in the engine currently and a 1956 here also (not being used). The 1956 measures 3.874~3.875" and a brand new Fel-Pro seal (held together tightly) measures 3.870". Holding it on the end of the crank, it isn't loose, but by the same token it isn't tight. There's an end gap, but a pretty doggone small one. I know from the past it would not seal for very long in the 1956 block...maybe 6 months to a year. It never seemed to be quite tight enough against the crank when I used it.

As for the 1959 engine, the clearance between my main bearing and crank journal at the rear was .0015 when it went together 2.5 ~3 years ago. I haven't checked lately, but I'd imagine it might be .002" or so now. When I put the engine together, knowing the problems I had with the 1956 block, I put a piece of copy paper between the crank and the Viton gasket. I stopped adding self-adhesive aluminum tape shims to the Viton piece when I got what I considered decent resistance top/bottom doing that (pulling the 1/2" wide piece of copy paper out). As I recall, each layer of the aluminum tape was .002" thick and I had to add 4 layers to get the seal to fit tightly enough.

As for offsetting the seal in the grooves, back when Fel-Pro was still making this seal I spoke with a gent (who had been there when this seal had been created...was retiring as I recall the week we talked). In that conversation, he mentioned they had reverted to telling people not to offset the 2 pieces. I asked him why and he said there were two reasons...one, people would not follow instructions...they'd offset the pieces too much...an inch or more and according to him that pretty well guaranteed they wouldn't work correctly and two, research they'd done indicated the ends butted together evenly at the joint would provide more uniform pressure on both sides of the joint which was how the seal was designed in the first place. He said if you thought you had to offset them not to rotate them by more than 1/16" inch at the very most. He also said it was important to remember to use a non-hardening sealer on the pieces where they went into the grooves.

Somebody wondered if anyone had disassembled a block in which the Viton seal had been there since the engine was new. Yes...at least I believe so. I was told by the prior owner the 1959 block I have had never been disassembled. It was obvious the water pump had been replaced and it had a rebuilt starter and generator, but no evidence of overhaul work at all. I took a picture showing one of the Viton seals I removed compared with a brand new one...below. The original had worn by almost 1mm and it had obviously been leaking back there.

I used the Best Gasket 4519S neoprene rear seals on my '61 261 and have had no leaks. I did have one heck of a time getting them in, though. I wish I could have done what Hotrod advises.