<VV> Bell Housing Seal

[corvairs]

Comments in text.

BobHelt at aol.com wrote:

> 
>In a message dated 7/1/2007 8:40:19 PM US Mountain Standard Time,  
>jb30343 at navix.net writes:
>
>Bob,  Would you mind explaining your reasoning?   Thanks.  --J.B.
>
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>Hi JB,
> 
>Gosh, i thought that would be obvious. 
>  
>
Don't you mean superficially obvious?

> 
>First, Polyacrylate is the same material that the second generation of Chev  
>pushrod tube O-rings were made of......that failed just as rapidly as the 
>Buna-N  ones. 
>
Not exactly. Current compound is improved.

>Polyacrylate has a much lower temperature acceptance than Viton.
>
Actually, it's only about 30 degrees less.

> So, 
>since  Viton was a superior material for O-rings, it too is superior for the 
>bell  housing seal. 
>
There is no logic there. Steel is a superior material to wood, but you 
can't burn it in a steam locomotive. Note that 99% of the time the o 
rings that fail from heat and age are the ones on the cylinder head. The 
block o rings are virtually never brittle or leaking. Considering the 
location of the crank seals (on either end) if you needed the extra 30 
degrees of protection you're in SERIOUS heat trouble with your engine.

>In my experience, viton wears and seals just as well as 
>the  others.
>
Well, according to the head engineers at Parker Seal, Viton does NOT 
wear like many other materials. This application of seal is called 
"dynamic" as opposed to "static" (like the o rings) and Viton is not 
thier preferred material.

>It just lasts longer before hardening up and failing to seal.
>  
>
Again, in this application it makes no difference. The real question is 
whether the Viton will wear as well and the conclusion is, at the least, 
controversial.

> 
>That is coupled with the problem that this seal is so difficult to replace  
>when it fails. You want to use the best seal possible.
>  
>
No argument there.

> 
>Then there are always the comments from Larry Claypool that the Viton  seal 
>is all he ever uses......
>  
>
Larry is a good friend and the only person I go to when I'm technically 
stumped. But his comments here baffle me. We discussed many times the 
problems he had had with bell housing seals. They all related to some 
seals on the market 5+ years ago that were dimensionally too large on 
the i.d. (They weren't from us by the way) What Larry had to do was use 
a redi-sleeve with those seals to keep them from leaking.  When I saw 
his note in the Clark's catalog it surprised me because the material the 
seals were made out of was never the issue in the first place. It was a 
question of the i.d. being the proper dimension.

When we (and Clarks) contracted to have the seals made (apparently, it 
turns out, from the same supplier) we both obviously insisted on having 
them made dimensionally correct. The seals were available to both of us 
in Poly or Viton. Clarks had both made - I (after advice from some of 
the country's foremost sealing experts) chose only the "poly".

The seals work because they are dimensionally correct - NOT because of 
the materials they are made of.  How could Larry (or anyone else) know 
that the Viton worked better because of it's compound when the seals had 
only been in use for less than 6 months (when the letter was written by 
Larry)?? I could understand 10 years later if the poly seals didn't hold 
up but the Viton did then you could make the argument......

But according to Parker, the reverse MAY be true. In 10 years the Viton 
seals may be worn out and poly seals will still be sealing. That's why I 
stayed away from them.  Temperature is NOT the issue in this application.

> 
>Then there is my experience of having to replace many a hard-as-rocks bell  
>housing seal that wouldn't seal.
>  
>
I don't doubt it, but older, inferior seal material plus other unknown 
factors (plus 40 years of use) etc etc may mean a lot of things  but it 
isn't an endorsement for dynamic Viton seals.

Lon
www.corvairunderground.com

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