Sam R
8mm Socket
Good morning folks,
Pictured is the guts from a smoked MS 271 that came in to the shop with a complaint of non-running.
Externally there was not much of note; except see the chain in the pictures. Every cutter tooth looked like the ones pictured. I'd never seen this before but I was told it's the result of running a dull chain so long that it actually begins to bevel the top of the cutter tooth.
Based on findings inside the cylinder & crankcase, I believe this saw was ran at excessive unloaded RPMs for an extended period of time as evidenced by the destroyed main bearings, bluing on the connecting rod and transfer/detonation on the exhaust side of the piston. There's a small amount of melt over the clutch side bearing and the clutch itself was almost completely blue.
Finally there's some build up in the crank pan which appears to either be material from the bearings & piston or it could possibly be where the oil broke down in the extreme heat. I believe the series of events leading to the total failure of the unit went something like: Excessive RPM > lubrication breakdown > bearing failure (followed closely by seal failure on clutch side) > swelling of piston in cylinder due to RPMs and lean condition > detonation from heat > loss of compression > total failure.
Pictured is the guts from a smoked MS 271 that came in to the shop with a complaint of non-running.
Externally there was not much of note; except see the chain in the pictures. Every cutter tooth looked like the ones pictured. I'd never seen this before but I was told it's the result of running a dull chain so long that it actually begins to bevel the top of the cutter tooth.
Based on findings inside the cylinder & crankcase, I believe this saw was ran at excessive unloaded RPMs for an extended period of time as evidenced by the destroyed main bearings, bluing on the connecting rod and transfer/detonation on the exhaust side of the piston. There's a small amount of melt over the clutch side bearing and the clutch itself was almost completely blue.
Finally there's some build up in the crank pan which appears to either be material from the bearings & piston or it could possibly be where the oil broke down in the extreme heat. I believe the series of events leading to the total failure of the unit went something like: Excessive RPM > lubrication breakdown > bearing failure (followed closely by seal failure on clutch side) > swelling of piston in cylinder due to RPMs and lean condition > detonation from heat > loss of compression > total failure.
