The transparent discoloration and absence of carbon on the piston crown surrounding the crater in the center, is a sign of severe piston crown over heating. Detonation causes severe piston crown overheating.
The crater forming in the center of the piston is from pre-ignition. The pre-ignition is the result of detonation. The carbon/discoloration over this crater is evidence that the crater was formed during one of his prior engine abuse sessions
The piston shows severe detonation damage around the whole circumference of the piston. The sand blasted looking band that is about 1/8" wide around the whole circumference is the result of detonation.
The missing piece of piston is the result of force the ring is placing on the weakened area at high RPM of a severely overheated piston. I do not think that the piece was burned away because the top of the piston shows damage from the pieces. If this area was burned away there would not be debris damage on other areas of the piston crown.
Typical causes of detonation:
1. Low octane rating can cause detonation.
2. Advanced ignition timing can cause detonation .
3. A lean air/fuel ratio can cause detonation.
4. High coolant temperature/engine temperature can cause detonation.
5. An exhaust system that is over-restricted can cause detonation. A carboned up stinger ID or carboned up spark arrestor are common causes of an over-restricted exhaust system.
Is you buddy deaf??
This engine was announcing it was having problems loud and clear right up to the moment of death. I have seen hundreds of engines with copycat damage as pictured.
Why is your buddy trying to save money by running pump gas on such an expensive engine like a KTM?
