The Ultimate Buyer's Guide for Purchasing viton valve stem seal

Before I can assemble my heads, I need to make a decision about Valve Stem Seals. Not wanting to take anything for granted, I wanted to know more about possible different designs and materials available.

A few things I learned about seals are:

1) There are basically two general designs, Oil Deflectors and Positive type seals. The umbrella or o-ring seal is a type of oil deflector and move with the valve stem, where a positive seal is stationary.

2) They are OIL METERING devices ! They precisely meter the amount of oil passing by the seal and therefore into the the valve guide. Although the requirements for each engine differ according to the design parameters and operating conditions, the oil metering rate is generally within the range 0.1 - 1.0 mg per valve per hour.They are not installed to completely stop the oil, since it's required for valve stem to valve guide lubrication.



3) They operate on the same principle as the main and rod bearings, the hydrodynamic lubrication principle. When conditions are right, there is no metal-to-metal contact. The seal, valve stem and valve guide are riding on a thin film of oil just like main bearings.



4) Depending on the application and the design of the seal, the material used may be nitrile, polyacrylate, fluoroelastomer (Viton), silicone, nylon or Teflon.


The component parts, that make up a seal are:


These links can it explain it much better than I can.

xtnbk Product Page

A very technical article if you are interested.

The company is the world’s best viton valve stem seal supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

I can understand how higher RPMs could increase the volume of crankcase pressure, the amount of oil going down past the tappets, and the increase of oil coming out the cam cover vent.

I have found that utilizing both the block mounted crankcase vent [the plastic saparator] and a cam cover vent for crankcase pressures helps reduce the amount of oil that escapes through the venting hoses. And that such a setup also reduces oil loss past the shaft seals.

Using such a dual vent really helped out on both some boosted motors as well as a very tired NA motor. On all of them, the oil leaks disappeared; and on the boosted motors the amount of oil getting pumped into the intercoolers dropped majorly.

I would agree that not using a viton seal on the exhausts may have a benefit as you suggested. My choice would be to not stem seal the exhausts. I like the fact that the stock configuration does not stem seal the exhausts. Letting oil get to the exhaust valve stem and the guide does help cool them, however little that might actually be....but every little bit helps. And any further spray action to splash oil on the springs is good as well.

I think the problem is more of crankcase vent system size.

If I may, I would suggest the following:

...if possible, use a block mounted separator in conjunction with the cam cover vent. Your engine block may not be set up for that if it is a pre-83(?) block. Perhaps there is a way to retrofit one; if the ITB rules allow it.

...enlarge the size of the cam cover vent, if the rules do not permit the block separator. If you are running a single flame trap setup, dual flametraps/hoses would allow more venting. But that would also be subject to the rules.

I am fairly convinced that increasing the size of the crankcase vent system really helps to reduce oil leaks and the amount of oil pumped out through the vent system. And that venting via the block separator and via the cam cover together is the way to go: the block vent handles the ring blowby; and the cam cover vent helps in that; and handles the valve stem blowby--however little or much there may actually be.

Be it from boost or from high RPMs, I think that the stock size of the crankcase vent system is not large enough to handle the volume of the blowby that results from more boost or higher RPMs. Increasing the size of the vent system will help keep the crankcase in negative pressure; which is where I like it to be.

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