MS250 compression

[a. palmer jr.]

Just wondering what your opinions are of the lowest compression you can run a Stihl MS250 at. I've got one here with 105-110 compression that I can't get to run and it feels kinda funny when I pull the starter rope, like it has compression with the piston going up and down. I tried draining the crankcase with the saw upside down overnight with spark plug out and just a small amount of mix was leaked out. I looked at the piston with muffler off and it's not scarred up.

 

[67L36Driver]

Shoot some mix oil in on top of the piston to raise comp enuf it will fire.[emoji848]

I ditch them (or save as parts) under 120.

 

[Basher]

I have rebuilt three of them that had the piston scored in the corners where it was very difficvult to see the scoring, either side of the exhaust and either side of the intake. Many call this cold seizure and happens when the piston expands quicker than the cylinder just after being started up from a cold sit situation. If you can feel drag as the piston moves up and down and it has low compression it is likely scored.

 

[a. palmer jr.]

I figure it has to be scored somewhere, just can't see it through the exhaust port..I'll probably be tearing it down later this year, right now I have 3 290s to rebuild and a 357xp.

 

[Skisawyer]

I have rebuilt three of them that had the piston scored in the corners where it was very difficvult to see the scoring, either side of the exhaust and either side of the intake. Many call this cold seizure and happens when the piston expands quicker than the cylinder just after being started up from a cold sit situation. If you can feel drag as the piston moves up and down and it has low compression it is likely scored.

I wonder how someone avoids this in a cold environment, winter, when you can’t preheat the saw. I run 40:1, I guess all I can do is let the saw idle up to operating temp before hitting the throttle.

 

[Basher]

I wonder how someone avoids this in a cold environment, winter, when you can’t preheat the saw. I run 40:1, I guess all I can do is let the saw idle up to operating temp before hitting the throttle.

Personally I have never scored a cylinder or piston and run saws in very cold conditions, I start them and let them idle for 2 - 3 mins before touching the trigger and then even wait a couple more before putting the saw in wood. The cold scored saws happen when a real cold saw is started and immediately put in wood running wide open, this causes the piston to expand faster than the cylinder, so I have been told by dealers mechanics that see this problem quite often.

 

[Skisawyer]

I’m gonna have to pull the muffler and see how my ms-25o liked the “cold supper” I fed it last winter. I put her to wood after about dislocating my shoulder on the first pull. It was good and hot when I shut it down.

I knew better, but when your snow machine is stuck and it’s dark and zero degrees F...

And maybe the moral of that story is run a cheap saw for winter sled duty, not the pro saw...

 

[Skisawyer]

Also, the vibration on a ms250 when the rubber bumpers are hard as a rock is pretty damn intense. This November I’m thankful for steel springs.

 

[Bigmac]

I wonder how someone avoids this in a cold environment, winter, when you can’t preheat the saw. I run 40:1, I guess all I can do is let the saw idle up to operating temp before hitting the throttle.

I always feel the cylinder fins, wait tell there warm before cutting, It never gets that cold here but always a good practice. Even on a warmer day, it surprises me how long it can take to get heat in the cylinder

 

[Basher]

On extreme cold days I carry the saws inside the truck so the heater gets them somewhat warm, have cut in -18 - 20F and not scored a saw yet, a little extra warm up time has saved my saws so far. If the saws have been left outside for a long period then a longer warmup time is all I can think of to prevent cold scoring. Sometimes the scoring cannot be seen from or through the exhaust port, its just in beyond sight lines from the port.

 

[Skisawyer]

@Basher Do you tape over or run the winter cover/shroud when it’s that cold?

 

[Basher]

@Basher Do you tape over or run the winter cover/shroud when it’s that cold?

I have never bothered with those little windows or shutters on the Stihl saws and run the same recoil sides year round. When its extremely cold I run my Arctic model saws if I have one that is correct size for the wood I am cutting, I have Arctic 026 and MS440`s, the rest are non Arctic and have performed very well for me at any temps. I don`t set them down in soft fluffy snow either running or shut down, that is where some get in troubles when the fan sucks snow in and it melts.

 

[Terry Syd]

On the issue of warm up for saws, when I was working with motorcycles I read a technical paper by KTM. They found if they gave a 3 minute warm up (idling) on an air-cooled engine, it extended the top end wear (rings, piston, cylinder) by 50%! Just let it idle for three minutes before putting a load on the engine.

On water-cooled engines it was a 5 minute warm up.

I start the saw, then go about putting my chaps on and various other tasks. By the time I'm ready to cut, the saw has warmed up.