Wanted to throw this one up for discussion as I am sure others have far my experience than I do.
I recently had my 18-RG head reconditioned to fix valve clearance gaps closing up. The cause of this was overheating valves due to minimal margin left on the valves.
All new valves were fitted, the standard cams re-ground, and some port work was done. The motor performed excellently with plenty of power.
10 000km later the head decided to drop a valve. Fortunately no other damage to the bottom end except a small mark on the piston due to the dropped valve.
Cause of problem according to the machining shop that did the original repairs was the valve guide moving in the head which has cause the collet to let go thus dropping the valve. (Valve guides were not changed during original work).
I was told that this was extremely rare, and extremely unlucky to happen.
Has anyone experienced similar problems?
The motor hasn't been driven hard and when the valve let go it was only revving at 2000 rpm.
It does happen sometimes, but saying how often, how likely etc is like asking how long is a piece of string....
It is kind of understandable if the guides weren't replaced, since the 18R-G heads have this completely abnormal valve stem diameter of 8.5mm (or something like that) which is totally different to everything else - hence guides are expensive.
I would just get the guides done - being an 8 valve head makes it very cheap if you remove the head yourself.
Tue, 29 June 2004 03:49
