Low Compression in #4 Cylinder that had a stuck valve

[Sailor Ron]

I had a stuck exhaust valve in #4 cylinder. Managed to free it using Marvel Mystery Oil and tapping it down with an allen key. Valve is now moving OK and cylinder is firing. But it has very low compression which does not increase when oil is added to cylinder. When the engine is running there is no audiable difference when spark plug is removed at low idle but there is some difference at fast idle.
My mechanic friend suspects carbon build resulting is a poor valve seat and that to protect the valve from burning out I should close gap on the spark plug so that this cylinder does not fire until I can remove the head in the fall and repair the valve seat.
Do folks agree with this approach? The engine runs smoothly on 3 cylinders.

[thatch]

Ron,
Welcome to the fray. Your mechanic sounds like a saavy kind of a guy and his approach of shorting out the #4 cyl certainly could save some seat damage while still allowing you to use the engine. It is entirely possible that while loostening the stuck valve with the allen wrench that the valve was actually bent in the process. Since you will be removing the head to fix the problem, my comment is probably a moot point. Depending on how handy you are, you may want to try pulling the head and doing the repair work yourself. In any event it would be a good idea to buy a copy of the Moyer repair/rebuild manual which is truly a "laymans" approach to repairing the A4.
Tom