someone needs to sticky this thing all over TT, for the half dozen JA that think you should lap the valves on install, like it is a 1970 small block chevy...
Interesting that it says the Wiseco valve is a "one piece" valve. I believe the stock Yamaha valves are two piece, welded together, which may be why they occasionally decide to break off.
This is exactly what I've been saying for years now.
The friction welding process by which Yamaha and most other two piece valves are made is usually not the reason for their occasional failure, the recall on the '06 YZ250F notwithstanding. The most common causes are timing failures that bring the valves into contact with the piston, and fatigue, usually aggravated by seats and valve faces wearing off center, and causing the valve to "scrub" and twist as it closes on the seat.
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