This one is interesting, so I decided to post it for feedback. A fellow brought in a Stihl MS 290 that had been running fine but he said it stopped and could not be restarted. Seemed like no compression, so I decided to tear it down and rebuild it. I measured compression at 70 psi, so the top end was a gone goose. First find was a ruptured intake manifold boot. The second find was a missing piston snap ring that had come loose and wrecked the piston and rings. Here's the proof:
View attachment 756619 I inserted the scrap paper to better show the two tears in the intake boot. What I would like to know is which one failed first? The intake boot or the piston's snap ring that came loose and bounced around inside the combustion chamber until it tore up the piston, the rings, and damaged the cylinder?
BTW, the spark plug was dry as a bone as if it had been heated with a torch. And, the piston, rings, and cylinder are undamaged and clean on the exhaust side. WDYT?