nylon VS rubber stem seals

[roanokeSpider]

Which is better?

[azygoustoyou]

Wouldn't nylon be more durable?

[manoa matt]

Also seen them in silicone. performancefiat.com

[engineerted]

Nylon? Who sells those. I thought there were only teflon and rubber.

Ted

[roanokeSpider]

Maybe teflon is the best their sold at IAP. I think I saw the nylon ones on Vicks website

[Daniel]

why is this posted in performance ?

[rlux4]

To get opinions on which would perform better?
Ron

[pope]

Usually any other material but rubber is listed in the performance sections of the catalogs. I think they are usually listed as upgrades for high performance engines, but surely would not hurt having them on our standard engines.

[Daniel]

oh i thought these were just supose to last longer then rubber my bad .

[manoa matt]

Let’s think about this from a materials/manufacturing stand point.

Nylon and Teflon are denser materials than Silicone or Rubber, and thus not as elastic. After looking at pictures of the Teflon and nylon valve stem seals it appears they do not contain the small spring like most typical oil seals. The spring is there to help hold the seal material against the shaft or sealing surface after the material itself has lost some of its elasticity.(mainly rubber that has undergone repeated heating/cooling cycles)

Since the Teflon and Nylon seals don't have the spring I'm guessing they must rely on a slight interference fit with the valve stem. Fortunately Teflon has the second lowest coefficient of friction of any material. So even with the seal tightly gripping the valve stem, it should still slide up and down through the seal pretty easily. I'm not sure about Nylon.

The questions are: Will the nylon and Teflon valve stem seals continue to be an interference fit with the valve stem after repeated heating and cooling cycles? Will the valve stem eventually wear enough surrounding material away to reduce the interference fit of the seal? Will the Teflon or nylon get damaged during the notoriously tricky valve stem seal installation?

I have a set of the silicone seals that I compared against some rubber ones. The silicone ones are definitely better quality than rubber, but I have yet to install them so I can't say how they perform. They were not much more expensive than the rubber ones and still about half the price of Teflon.

Obviously there will not be any noticeable or even measurable gains. The ultimate goal is to keep the oil from running down the valve guide into the combustion chamber. I think realistically they will all "perform" the same, its a matter of which one is going to keep oil out of the guide for the longest amount of time, because replacing them is not an easy task.

How about we discuss the pros and cons of rubber, vs, polyurethane, vs, derlin control arm bushings? Same argument.

[pastaroni34]

I urge you to use Viton or Teflon. Personally I would go with Viton, as I have no direct experience with Teflon seals on a Fiat.. I have used these on Porsche motors but I cannot vouch for Fiat ones, and to make matters worse different manufacturers use different tolerances, resulting in different performance from seals. Teflon has a reputation for being "too good" of a seal and not allowing enough oil past to lubricate the valve stems. The amount of oil required for the valve stems is a function of valve stem and guide material and manufacture.. again a complicated subject.. think of it this way, Viton is more of a general purpose seal that works well in all situations, Teflon is more of a high-strung solution that requires 'tuning' other engine components to work with it properly.

Anyway, Viton is superior to silicone, and nitrile rubber. Its not worth your time to put in the lesser quality parts.