2003 Ski-Doo ZX Series Factory Shop Manual, Page 67Get this manual

2003 Ski-Doo ZX Series Factory Shop Manual, Page 67

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Section 03 TROUBLESHOOTING Subsection 02 (ENGINE)
4 Melted andor perforated piston dome; melted section at ring end gapaWhen piston reaches TDC, mixture is ignited by heated areas in combustion