[Amc-list] Bronze Valve Guides & Seals

["Bruce Hevner" <scramblr@xxxxxxxxxxx>]

While using the guides you have referred to will work (I used to MAKE
Bronze guides) I have some advice from 40 years of using them. You
should NOT use the white Teflon seals with them, especially if it's a
street motor!!
 
The white Teflon seal is really for hi-performance use where spring size
will not allow anything else to fit. It does NOT work well on the street
under high vacuum conditions. I ONLY use them as a last resort where
nothing else will fit. You would not think something made from Teflon
would wear steel but they will! Hard chrome resists wear from the seal
pretty well but standard valves will end up with a "notch" where the
seal contacts it.

 These seals are difficult to install over the valve stem and grip it
tightly when new causing some to believe (erroneously) that they might
"dry up" the guide. In reality the reverse is true! Being a "square"
type seal they don't do a good job of sealing and maintain the same
pressure on the valve under all conditions. Over the years I have seen
time and time again oil usage caused by these seals. Better than nothing
but not by much.

If you will look at most late model OEM seals (especially OHC heads) you
will see they have went to the "flexible lip" type seal. Kind of looks
like a small crankshaft or camshaft seal. These type seals have several
major advantages over the Teflon seal.
Having a small spring they maintain contact with the moving stem better
than the Teflon seal. By design the seal has a low drag on the stem
under low vacuum but as vacuum rises the seal grips the stem tighter
causing it to seal better. Exactly what you want it to do! And believe
it or not there is VACUUM in the exhaust port too. 
 Since most of the time they have low drag on the stem they do not show
the stem wear that the Teflon seal does. 

They do have a few disadvantages though. Being subjected to the high
heat of the stem (especially exhaust) they need to be made of high
quality material which adds to their cost. And it's hard to find them in
the .500 diameter that some of these bronze guides are made to. If you
can, try and use a guide which has a .530 top diameter. This makes it
MUCH easier to find lip seals for them and creates a "shoulder" to help
keep them from moving in the head.

A company called Enginetech
(http://www.enginetech.com/pr_valvestemseal.php) has some VERY high
quality lip seals which worked GREAT for me. They were only available in
bulk packs of 100 but we used LOTS of them so that was not a problem.
Contact them for a local distributor.
But HEY,,, that's just ME!
Bruce Hevner


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