rubber head parts?

[mtn goat]

I finally recieved a new head for the o'l girl and noticed that the guide caps(i think thats what you call them, sits under the spring over the guide...maybe they are stem seals...I dont know) anyhow, they are rubber. my old ones were nylon or some sort of polymer. What is better in this case, and is it worth replacing if the nylon is better.

[jeepbob]

Your old hard seals usually end up in the oil pan when they start to break, they can even plug up the oil returns. If you have the tools to do them on the with the heads on or you are pulling the heads, it is worth the effort to put on the new rubber ones.

[Lindel]

Yup, valve stem seals, or "umbrella" seals. They keep excess oil from sneaking past the valve stem, into the combustion chamber.

Keeps the blue cloud at start-up down to a minimum.

[mtn goat]

So from what jeepbob said, I gather the rubber ones are more desirable. The head is on the front seat so it would be easy to change over nylon if I need to (dont worry, I wont reuse the old ones)

[Lindel]

If you do use the nylon seals, you'll need to warm them up in a pan of water, so they'll fit over the valve stem. Otherwise, you'll break them trying to put them on.

Get the water to boiling, then drop them in for a few minutes, but move quick when you go to put them on, cause they'll cool quickly.