What makes the valve guide seals fail?

Just curious as to what makes the valve guide seals fail on these things? I am in the process of selling my XR, and unfortunately if its been sitting for a few days, it will smoke quite a bit on start up until it warms up. Run it often, and it smokes very little. I did a compression test, and it made 180 PSI so the rings are still healthy.

Anything I can do to reduce the seal leakage, or convince the buyer that with 180 PSI compression the engine is still healthy, even if it does smoke some on startup.

With 180psi it sounds like a healthy engine to me.

Oil going down the guides provide lubrication, air cooled engines need more than water cooled engines because of the wider range of operating temperatures.

A very miniscule amount of oil makes a lot of smoke. Run the engine before a buyer comes to look at it. Also run it outside.

Heat and dirt. Run it to lean and the motor runs hot and eventually cooks the seals.

Dirty oil or dirty airfilter allow dirt to stick to the valve shaft and this is forced up to the seal wearing it out.

Anyone change the seals without taking off the head? I know you can do it to a car motor with the right spring compressor. I need to find that style small enough for the little motors. I have one that smokes at startup for 45 seconds or so ...was thinking of changing the seals one day.

I told the buyer about the valve seals, and that the smoke clears up once the engine warms up. He didn't seem to mind too much, and the 180 PSI compression sealed the deal. Sold it for $800, was hoping to get a bit more, but I guess I can't really complain since we bought the bike for $800 4 years ago...

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