cwatkin
ArboristSite Member
I have had excellent service at of all my Stihl saws including this M-250 that had probably served well beyond expectations. I suspect it is done for after a recent incident but figured I would ask.
The saw had been used and abused on my farm. It never seemed quite the same after a tree fell and pinched the bar during cutting. It didn't just bind the saw. It pulled the chain so hard that it ripped all the teeth off the drive sprocket, split the end of the bar down the middle, destroyed the tensioner, and ripped the bar nut studs out of of the plastic housing. I was about to write the saw off at this time and then realized I had a parts saw that someone had given me from a similar model Stihl. I pulled all the parts I needed and got the saw working again. It needed a new bar, chain, studs, sprocket, tensioner, etc.
I JB Welded the studs back in position. One held and one didn't so I only have one bar nut present. I figured any extra use from this saw was money in the bank and I had a larger backup if needed so wasn't too worried. I also suspect that the stress placed on the crank at this time somehow damaged the engine internally as it was running oddly at times. It was harder to start and sometimes was hard to keep running at idle.
Anyway, I was trimming some branches along a fence line when it started to sound like it was running a tad lean like if you were about out of gas. I knew this wasn't the case as I had just filled it up. It then ran normal for a few minutes and then the saw went into a runaway mode where throttle control or turning if off (killing spark) had no impact. The saw was just screaming. I tried to choke it to death and that had no impact. I probably should have dumped the gas out at this time but I was more worried about keeping the runaway saw away from me or the ground.
It ran for about a minute like this and then it started to bog and a shower of sparks began to come out of the exhaust. I figure the piston was getting so hot as to melt at this time. It then stopped dead and was locked up hard. Smoke was just pouring of the saw from all areas and you could feel heat radiating so it must have been extremely hot. It was still locked up the next day so figure it is really locked up.
I checked to see if the carb had come loose creating an intake leak and it was tight. I talked to a guy who works on these for a living and he said it probably had a small hole in the piston allowing it to still run but suck air from the crankcase and run lean. I always keep my saws tuned a tad richer than from factory as my local shop says they last a lot longer if you do this so don't think this was an issue.
I figure this unit is best used as parts for the new MS-250 I plan to replace it with and not consider rebuilding it with all it has gone through. I have found some piston and cylinder kits for not much more than $50 that were rated well online. I don't know if this would fix it or if other major damage was likely done and if I should just buy a new saw and keep this one for parts like I originally planned.
What do you suggest? Also, what do you think happened and do you think I could have saved the saw from this suicide mode it went into safely? I had something along these lines occur with a cheap consumer grade trimmer once. It had fixed carb jets so was tuned lean for the EPA of course. It decided to run away from me on a really hot day and tried to run backwards, shearing the flywheel key. The key was integral to the flywheel which cost more than I paid for the unit new. I hated the thing so gladly set it at the curb for scavengers to pickup and went out and bought a Stihl.
Conor
The saw had been used and abused on my farm. It never seemed quite the same after a tree fell and pinched the bar during cutting. It didn't just bind the saw. It pulled the chain so hard that it ripped all the teeth off the drive sprocket, split the end of the bar down the middle, destroyed the tensioner, and ripped the bar nut studs out of of the plastic housing. I was about to write the saw off at this time and then realized I had a parts saw that someone had given me from a similar model Stihl. I pulled all the parts I needed and got the saw working again. It needed a new bar, chain, studs, sprocket, tensioner, etc.
I JB Welded the studs back in position. One held and one didn't so I only have one bar nut present. I figured any extra use from this saw was money in the bank and I had a larger backup if needed so wasn't too worried. I also suspect that the stress placed on the crank at this time somehow damaged the engine internally as it was running oddly at times. It was harder to start and sometimes was hard to keep running at idle.
Anyway, I was trimming some branches along a fence line when it started to sound like it was running a tad lean like if you were about out of gas. I knew this wasn't the case as I had just filled it up. It then ran normal for a few minutes and then the saw went into a runaway mode where throttle control or turning if off (killing spark) had no impact. The saw was just screaming. I tried to choke it to death and that had no impact. I probably should have dumped the gas out at this time but I was more worried about keeping the runaway saw away from me or the ground.
It ran for about a minute like this and then it started to bog and a shower of sparks began to come out of the exhaust. I figure the piston was getting so hot as to melt at this time. It then stopped dead and was locked up hard. Smoke was just pouring of the saw from all areas and you could feel heat radiating so it must have been extremely hot. It was still locked up the next day so figure it is really locked up.
I checked to see if the carb had come loose creating an intake leak and it was tight. I talked to a guy who works on these for a living and he said it probably had a small hole in the piston allowing it to still run but suck air from the crankcase and run lean. I always keep my saws tuned a tad richer than from factory as my local shop says they last a lot longer if you do this so don't think this was an issue.
I figure this unit is best used as parts for the new MS-250 I plan to replace it with and not consider rebuilding it with all it has gone through. I have found some piston and cylinder kits for not much more than $50 that were rated well online. I don't know if this would fix it or if other major damage was likely done and if I should just buy a new saw and keep this one for parts like I originally planned.
What do you suggest? Also, what do you think happened and do you think I could have saved the saw from this suicide mode it went into safely? I had something along these lines occur with a cheap consumer grade trimmer once. It had fixed carb jets so was tuned lean for the EPA of course. It decided to run away from me on a really hot day and tried to run backwards, shearing the flywheel key. The key was integral to the flywheel which cost more than I paid for the unit new. I hated the thing so gladly set it at the curb for scavengers to pickup and went out and bought a Stihl.
Conor
