Posts
35
Joined
10/16/2017
Location
Valley Park, MO
US
Dennis_Fitzpatrick
2/6/2021 11:53am
2/6/2021 11:53am
Edited Date/Time
2/7/2021 1:38pm
My son and I picked up a 1996 WR250ZH and are in the process of doing a partial restoration on it. It ran before tearing it down, but take a look at the exhaust side of this piston crown. It’s eroded and curved. I’ll be having the cylinder bored and will be putting in a new piston kit. Does anyone know what could have caused the piston crown erosion?
The Shop
-low quality fuel
-incorrect ignition timing (follow service manual instructions to verify correct ignition timing)
-excessive combustion temperature (caused by lean condition)
-excessive compression (probably not the culprit as the head is most likely stock. A thinner base gasket can cause this)
-incorrect heat range of spark plug.
You will have to do some CSI work to determine the root cause of the detonation. Air leaks can cause a lean condition, incorrect ignition timing etc....
One bit of advice it to make sure the powervalve stop (left side cap on cylinder) is not worn. This will allow the powervalve to over-rotate and encroach into the cylinder and snag the piston ring. This is a well known failure point of that motor. Good luck!
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