Last month I asked a Stihl dealer to repair an MS 660 that had lost a small chunk off the top of the piston after about 500 hours of use. He replaced the piston, the rings, and the cylinder. After about 60 hours, the engine shut down again this week. This time we had a strange uneven wear problem. The intake side of the piston, cylinder, and rings is clean as a whistle. Here's a shot of the piston after I removed it:
However, the exhaust side of the piston is shot. The rings are burned out and fused to the walls, and the inside of the cylinder mirrors the piston with wear streaks everywhere:
The piston was actually loose inside the cylinder, so compression was almost zip. All other parts seem OK (bearings, crank shaft, etc). This time I'm going to rebuild the engine myself. Does anybody have a clue what caused this so that I can tell the operator after I fix it again? Maybe he can take corrective action. This seems goofy. TIA.
However, the exhaust side of the piston is shot. The rings are burned out and fused to the walls, and the inside of the cylinder mirrors the piston with wear streaks everywhere:
The piston was actually loose inside the cylinder, so compression was almost zip. All other parts seem OK (bearings, crank shaft, etc). This time I'm going to rebuild the engine myself. Does anybody have a clue what caused this so that I can tell the operator after I fix it again? Maybe he can take corrective action. This seems goofy. TIA.
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