Viton vs Teflon valve seals

If the heads are cut for PC seals absolutely go with Viton.

I don't use either for double springs on 3/8" stock valve guide tops that I don't want to cut. I am not that big a fan of PC seals and I like the guides to get a little more oil.

One particular set of double springs I use has a .700" id on the inner spring, so using umbrella seals is obviously out unless you trim them into disk.

So years ago I just started using square profile, high temperature (400F), silicone o-rings that have a .637" od that I buy from McMaster-Carr McMaster-Carr

I assemble the o-ring right against the top of the guide and once the engine is rotated the o-ring slides up the valve stem whatever the lift of the cam.

Since oil comes sliding down the valve stems from above through the two gaps in the valve keepers it really isn't an issue letting the o-ring ride on the stem to deflect the oil.

I run my 499" street engine with this setup and have no issues using the o-rings.

Tom