View original topic: rear main seal flush or countersunk
Boogie Child Wed Apr 26, 2017 11:15 pm

Putting in a new seal and Boston Bob says it should be counter sunk ie bottomed out. Tom Wilson says leave it flush with the case not to bottom it out. Both well respected minds, thoughts and comments from the crew please, who does what. I am using one of the go westy seals which are supposed to be superior and a little wider (deeper) so maybe I dont have an option any one used these seals? comments thanks.

lil-jinx Thu Apr 27, 2017 2:58 am

I flush mounted mine,as most{non vw} seals I have seen are flush.If it is flush,then you know it is in square and if you bottom it then you leave a ledge outside of the seal that could collect dirt and dust.

Wildthings Thu Apr 27, 2017 4:14 am

How badly grooved is your flywheel? If badly grooved you don't want the lip of your new seal to run in the groove and may want to vary the depth of your new seal accordingly.

raygreenwood Thu Apr 27, 2017 7:52 am

There are two seals. Both are designed as Lil jinx be installed all the way bottommed out on the ledge. If it isn't ....and the seal is sealing.....and it slips in further to the ledge while will leak like hell.

The thicker seal (11.5mm to 12mm) is technically a vanagon part. This is why you find them at Go westy. That seal ran in a bore that was usually about 11.5mm deep so the seal protrudes slightly. The part # is 021 105 245 C.

There were....for reasons unknown some non vanagon type 4 engines that came from the factory with a 12mm seal bore and the thicker seal. I have personally found about 6 of them over the years.

The thinner seal is part # 029 105 245 B its typically listed as 9mm thick. The bore depth in the case ranges from 9mm to close to 9.5mm. When installed this seal can be dead flush or very slightly below flush.

Whether they are flush or raised slightly above the seal bore has to do with what the actual bore depth is.
You need to measure the bore.
If you have a deep bore seal area.....and put in the thinner seal it will almost always leak intermittently as there will not be enough seal lip tension on the tapered snout of the crank.

If your crank endplay is also toward the high end of the spec and you either have high piston blow-by or poor crankcase ventilation.....the leakage will get ugly at highway speeds. I have heard that a few people have gotten away with using the thick seal in the shallower bore to fix an out of spec crank snout......but I have never done it and you will have a lot of seal mashing against the back of the flywheel.

Boogie Child Thu Apr 27, 2017 8:04 am

Thanks for the replies. I think Tom Wilson's theory has to do with wildthings point of flywheels that are grooved I will adjust accordingly.

raygreenwood Thu Apr 27, 2017 10:12 am

Boogie Child wrote: Thanks for the replies. I think Tom Wilson's theory has to do with wildthings point of flywheels that are grooved I will adjust accordingly.

No....I doubt that. Unless Wilson explains that he is moving the seal around to work around a flywheel that has a groove in it...dont assume that he is working along that theory. The factory never did that. If you had a groove in the replace it.

While moving the seal in or out is sound advice to counteract a grooved flywheel....its "aftermarket" knowledge from experience and not perfect information. Its what you do to get by.

Wilsons book was published in January of 1987. That means...back in that day....all of his information was gathered and submitted by somewhere in the spring or summer of 1986.

The thicker 12mm seal is a waterboxer part. Those engines were being made from August of 1982 onward. They had only been in production for a few years when wilson was working on his book.
I have not dived into my wilsons book in quite a while...but from memory there is not one mention of the thicker Waterboxer/Vanagon seal in the information is incomplete and should not be taken as such.

Either way....the seal MUST be driven down to the supporting ledge. This is the only way you can insure that its square and remains immobile.

The problem found over the that there is variation in seal thickness by brand, material and manufacturer. This goes for both the thinner seal and the thicker seal.

Its so happens...that when driving some seals all the way to the ledge like they should find out one seal is a few 10ths of a millimeter thinner...and will not sit flush...but is countersunk. By design...they should be flush with the outer surface from all of the publications i can find.

As I mentioned...measure the bore....then measure the seal.

By my experience....those really nice dual material...silicone/Viton (orange and black) Victor Reinz seals....awesome materials by the way....have tended to be on the thinner side over the years and I have had the most problems with them.

If you find you have a case with the 12mm bore...which is actually about 11.25 to 11.5mm...the seal when seated on the ledge will stand proud of the case by 0.5mm to 0.75mm...and works perfectly.

In a pinch....when I was first discovering that I had a case with the 12mm seal bore....and did not yet know it was a Vanagon seal....I fixed it by buying a big internal snap ring...actually whats called a "twist on internal retaining ring"...of about 3.75"... and sanded it to the correct thickness...seated it on the ledge and drove in the seal. Worked perfectly but you must make sure that it does not impinge on the shims.

Also....there is a LOT of confusion in the actual seal part #'s.

German supply lists this as the "thicker" 12mm seal...Part # 021 105 245 C
Nice one too...the high temp silicone seal.

German supply lists this one as the Victor Reinze dual material "thin" seal part #029 105 245 B

Now....the parts catalog for VW type 4 (411/412) notes the use of part # 021 105 245 C as the factory stock seal. I know from long experience that the vast majority of 411/412 with 1.7L and 1.8L engines (as well as Porsche 914 1.7L and 1.8L) came with the thinner seal and seal bore. this just German supply making the 021 105 245 C a universal in their books?

I think back in the day....many shops had these seals...thick and thin...mixed up in their parts bins and had no separate part that time. lists the 029 105 245 B as type 4 flywheel end dimensions listed

All I can say for sure is measure the bore depth and buy a seal that fits flush when driven down to the a minimum. In none of these engines that I have seen...whether shallow or deep bore...having the seal protrude 0.5-1.0mm above flush hurts nothing and may be the difference between sealing and chronic leaking.

Some very good information on this issue:


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