Valve Seals - Use them or not?

[Tom Cole]

I have built quite a few Yamaha YF200R1 engines.  It is basically a single cylinder version of the same engine we use.  The valve guides and the valve seals are the same in both engines.

It was necessary to modify and upgrade the valve train in this engine in order to maximize intake flow.  That modification required the use of a valve spring retainer that would collide with the intake valve guide seal, so the seal had to be removed.

We saw no ill effects of running without the seal, and in fact, actually got less vlave stem and guide wear over the year.

Have any of you tried this on a 1200?  Every built head I have seen has the seals installed, and I'm wondering if the only reason they are there is because nobody has tried it without them.  Seals are generally designed to reduce oil consumption over long oil change intervals, which we do not incurr.  The seals therefore can starve the guide for oil causing friction, heat, and wear.

I also wonder about the potential lubrication that a slight amount of oil leakage past the intake valves could give to the combustion chamber.  Since the fuel in the tank has a specific gravity spec, this could help with friction and heat in the combustion chamber.

I'd love to hear any thoughts.

[elimn8u_43]

I just built a head for my dad's car and I did not install the exhaust valve seals. I used them on the intake because of the vacum in the ports maybe pulling excessive oil into the cylinder. I have built many american race engines and have never used valve seals with no adverse affects. I have even seen very small horsepower gains on the dyno due to the friction loss.

Geoff

[Tom Cole]

Thanks for your input...anyone else?

I'm going to try it without the seals.