Exhaust Valve gear grinded?

Mine's not perfect on my '03. If it looks pretty bad of course I would go ahead and replace it. I really don't know what causes these things to wear the way they do, unless carbon buildup causes them to slip and grind. If that's the only damage you have your doing pretty good. Is your piston stock?

My guess would be from carbon build up or mabye there were some debris in there that caused it to stick. The piston with the B on top is a proX / stock piston.

John,

Replace the powervalve. It will be stripped by the time you next need to do a set of rings. It is a problem with the 1989-1994 KDX200s.

That’s a common problem with the 89-94 200s. One of two things happen. Either the sub port valves become carbon seized in their bore causing the actuator rod to strip the gear or the hole in where the valve fits in the bottom of the sub-port valves bore become s enlarged over time and allows the valve to lean on an angle and bind. It’s important to check the condition of the hole before installing a new valve. If the hole is enlarged there are a couple things that you can do to fix it. One is to bring the cylinder to a machine shop and have them machine and install a brass bushing to restore the hole to its original size. The second is to purposely deform the aluminum around the hole reducing its size. This is what most people will do. Basically you use a punch and hammer and make four punch marks equally around the hole then test fit the valve. Punch in the same four holes until the hole is reduced to an appropriate size. I would punch about 3 or 4mm from the hole. Once the valve was fitting snug again I would punch it one more time then resize the hole to the appropriate size by carefully drilling it out again with an appropriate sized bit. It sounds brutal but it works and will prevent you form continually breaking valves. It will also be important to properly jet the carb to avoid running excessively rich and to clean the valves when ever the motor is apart for service.

David