Frank, Robert, et al (who's al?),
Reading over the various posts, I'll try to shed some light from my
experience.
O-ring valve stem seals are meant to ride on the valve stem. They end
up
in one position on the stem, and are meant to deflect the oil that might be
running down the stem. Most LBCs have them on intakes only, btw.
Top hat style also ride on the stem as above, but deflect the oil
farther,
hopefully.
Valve Guide seals, aka, Perfect Circle seals, etc. are designed to fit
over the guide. There is usually a groove in the guide that "locks" the
seal in place.
The first 2 types usually fall off, in my experience on LBCs, VWs
Volvos.
The 3rd is most desirable for oil control, with this caveat... they
should
NOT be used on iron guides. The cast iron guides that are original on LBCs
among many others, need the lubrication that finds its way to the stem.
Bronze or silicon-bronze guides can use the 3rd type, which more and more
seem to be made of Teflon-like material, often white, at least for European
cars. The bronze guides do not require the lubrication of the iron guides,
and are often "rifled".
So, IMHO, if you keep iron guides, you have to suffer the o-ring or
umbrella seals. An improvement in both performance and oil control can be
achieved by "rifling" the inside of the iron guide. I do not recommend
guide seals on iron guides. If you are doing a rebuild, replace the guides
with bronze and have them cut for Teflon seals.
Hope this helps.
Peter C.
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