This thread covers the teardown of a 79.5cc Chinese clone engine that was used on a small 1500W generator. Failure occured after some 4,000 hours of operation.
Engine had been treated with a one time treatment of one heaping teaspoon of pure molybdenum disulphide powder on third oil change. Oil was changed roughly weekly, but sometimes not for a couple of weeks.
The actual failure was caused by the rivets on the cam that hold the decompression pall worked loose. This alowed the pall to move sideways. Edge of pall basically beat the crap out of the cam drive gear on crankshaft. Distorting teeth of gear bad enough for gear teeth to bind up.
What is truly remarkable about the engine is the pristine condition the cylinder, piston and connecting rod bearing are in after 4,000 hours of operation. The only other preventative thing done to rngine was the addition of a drail plug magnet to collect any loose wear particles. Magnet was eiped clean with every oil change. Only cleaning done on thid teardown was drain oil and wipe residue with shop towels.
Here us link to photo series: Moly Treated Engine Teardown