Stihl MS251 1 year old burnt out?

[c2far]

I was using my Stihl MS 251 chainsaw last weekend helping a friend cut the stumps off a number of small trees and he wanted the cut as close to the ground as possible without getting the bar & chain into the earth. Approaching lunch time and the saw had been working fine all morning without any sign of a problem I turned the saw off. After lunch I went to restart my saw when I immediately noticed virtually no resistance when I pulled the starter cord. The saw was clearly damaged in some way. When I got home I took the muffler off so I could see into the exhaust port. I noticed the piston top appears to be broken around the top circumference and vertical scratch lines along the piston surface so something has obviously damaged the Stihl question what?

The fuel was new, 5 litres unleaded petrol purchased only a few days before, I had mixed one of the Stihl two-stroke 100ml oil cartons sin the petrol container and shaken well so I recon the fuel mix will have been ok.

What I would like to know is if it was a result of me cutting the stumps close to the ground, I could feel the hot exhaust gasses wafting up to me due to the saws close proximity to the ground, and the tree stump and because the saw was on its side the exhaust gasses did not have as much space to escape as they would have had if I was using the saw limbing a branch etc.

Could this have caused the Stihl to overheat and damaged the piston?

The Stihl is just over a year old, and only gets the occasional use so I am hoping the 2-year guarantee will cover the repair. I have not adjusted any carb settings so they are as from the factory, and the saw has always ran well and cuts logs and branches like a hot knife through butter, I always use a sharp chain, so if any experts out there can offer me any advice as to why the piston has become damaged, and why this would result in virtually no compression I would be grateful

[gensetsteve]

Spud would be the best man to give an answer. Sounds to me like the carb was set up before the saw was run in and needed retuning as the saw loosened up especially as it was cutting so well sounds like it was running lean.

[eldon]

I had an MS251 bought new for one month. Partially pulled the bar stud out and returned it under warranty. Stihl apparently weren't going to replace the damaged case and just bodge up the stud.

I complained to the supplying dealer that the saw was rubbish to fail in such short time and wouldn't accept it bodged up. To be fair to the dealer (Andrews in Sherburn in Elmet) he realised I was disatisfied and offered a full credit towards the MS261 at my request. Can't be fairer than that can he?

Far better saw in build construction, just little bits here and there.

 

Liked my 251 for what I'm doing (firewood for home) but with such an early failure I lost all confidence. Hope you get a better response from Stihl and yes it sounds like it was running lean. The 261 has autotune but can't remember if the 251 does or not?

[doobin]

I do love my MS250 but it's clearly a cheaply built saw. Oiler is temperamental, the plastic around the clutch is not in good shape and I'm not sure how long it will last! That said, I only paid £40 for it so I will run it into the ground and then get an MS241 Same power and .2kg lighter, plus pro build.

 

They don't half fly with a 1.1mm 12 or 14" bar on.

[spudulike]

The most common reasons for seized saws are: -

 

1) Incorrect carb H screw setting

2) Old fuel where the petrol has destroyed the two stroke oil in the mix

3) Air leak - typically crank seals, split inlet manifold or impulse line

4) Split fuel line

5) Blocked fuel tank breather

 

The description "I noticed the piston top appears to be broken around the top " needs clarifying as a seize causes little damage to the piston crown but does cause bad scoring predominantly on the exhaust port side.

 

Not too much will destroy a piston crown, heavy detonation, a dropped decomp valve, ingress of a nut/screw into the carb, snagged ring on the downward power stroke are a few and numptey maintenance with misguided use of piston stops should be included!

[5 shires]

I was using my Stihl MS 251 chainsaw last weekend helping a friend cut the stumps off a number of small trees and he wanted the cut as close to the ground as possible without getting the bar & chain into the earth. Approaching lunch time and the saw had been working fine all morning without any sign of a problem I turned the saw off. After lunch I went to restart my saw when I immediately noticed virtually no resistance when I pulled the starter cord. The saw was clearly damaged in some way. When I got home I took the muffler off so I could see into the exhaust port. I noticed the piston top appears to be broken around the top circumference and vertical scratch lines along the piston surface so something has obviously damaged the Stihl question what?

The fuel was new, 5 litres unleaded petrol purchased only a few days before, I had mixed one of the Stihl two-stroke 100ml oil cartons sin the petrol container and shaken well so I recon the fuel mix will have been ok.

What I would like to know is if it was a result of me cutting the stumps close to the ground, I could feel the hot exhaust gasses wafting up to me due to the saws close proximity to the ground, and the tree stump and because the saw was on its side the exhaust gasses did not have as much space to escape as they would have had if I was using the saw limbing a branch etc.

Could this have caused the Stihl to overheat and damaged the piston?

The Stihl is just over a year old, and only gets the occasional use so I am hoping the 2-year guarantee will cover the repair. I have not adjusted any carb settings so they are as from the factory, and the saw has always ran well and cuts logs and branches like a hot knife through butter, I always use a sharp chain, so if any experts out there can offer me any advice as to why the piston has become damaged, and why this would result in virtually no compression I would be grateful

 

You using it for prolong time with exhaust close to ground Would't cause any damage,it would more then likely just cut out. My guess going by your description would be not Enough oil in the petrol mix which has caused the piston to lift.

[Daythe trees]

Doobin, I had one of the early 241's and returned it as the chip would decide to reset and take half a second to do it randomly. Sounds like nothing until you are back cutting leaning larch chasing the hinge when it's too small to dog tooth and it does so as the tree starts to move. Removes money when the first four foot is barber chaired due to the saw throwing a fit. I am sure it has been fixed by now. Other than that it is a lovely saw, well balanced and cuts well on a twelve bar, so light and easy to handle. I just didn't trust it with my safety.

[woodyguy]

Love my 241. Great little saw and the auto tune works a treat.

[SawTroll]

If the carb adjustment never was checked after it left the factory, it is very likely that a lean carb setting was at least part of the reason that the saw failed. Many models are set on the lean side at the factory, to make sure they pass an emission inspection.

The dealer should at least check the adjustment at the point of sale, and preferably ask you to at least come back for a recheck after initial run-in (some say 10 tanks, some say 10 litres of fue)l.

The safest way is of course to learn how to do it yourself, and check more often.

 

 

...or simply buy an auto-tune saw!

[cornish wood burner]

Could the exhaust gas have been drawn into the saw and disrupted the cooling?

Along with another problem such as a weak mixture tipping the balance causing an overheat.

I am not a chainsaw engineer so I would be interested in an expert opinion on this as sometimes I use my saws in confined places