Could I fix my Stihl MS 250?

It is possible this repairman is full of bull and whiskey. This is a depressed part of NH! I have also brought my snow blower in for repair at this shop and was not too excited about the diagnosis and estimate.

I would like to thank Stihlhead for his detailed responses! I feel as though I should print them out and use a highlighter for certain parts. All good info and I appreciate it.

I have not pulled apart the MS 250 yet as I am knee deep in building a new bedroom. Our family is growing this June! Another helper to stack and haul wood!

Well after many months of other distractions, the tear down of the MS 250 is complete! Anyone taking bets on whether or not I can put this back together?

Going back to last year the repair shop declared the piston and cylinder "junk." Here is a side-by-side of the new and old piston.


And here is the new and old cylinder.

Have A look at this video.Hope this will assist you, Ken

Keep the updates coming Don, I'll stay tuned.

StihlHead: Awesome info! But, I thought most 2-stroke oils sold for outdoor power equipment already had a fuel stabilizer additive... hence no Sta-Bil required. No?

donmattingly: I've heard a lot of the aftermarket piston/cylinder assemblies sold for Stihl have poor fit, and thus very short life. I've seen saw shops make a big deal about using only OEM Stihl parts in their repairs, one citing this as a reason. Might be worth researching, if buying a new assembly.

Cripes. Don't make it more complicated than it is......I have an Echo CS400. I buy the one-shot bottles of Echo oil. Add 1 gallon of gas & done, no measuring. Guaranteed to meet Echo requirements, and hold up the warranty. No thinking involved. I also buy the premium gas. Again, no thinking. To this gas I add StarTron additive. I have been told NOT to use Stabil red, only the marine blue. And ST is just as good. Also, for long term storage, my local shop carries Tru Fuel, gas W/O any alcohol. Lasts up to 2 years. Pricey, but worth it.

My saw has never failed to run doing this, and this spring I started out using last season's gas. No problem.

2-stroke oils may or may not have gas stabilizer in them. The type of Elf oil that I use is designed for 2-stroke motorcycles, and does not have stabilizer in it. In any case, I do not believe that there is nearly enough stabilizer in any of the outdoor power equipment oil to keep the gas fesh for long periods, or to protect phase separation from happening in ethanol blended gasoline. Also if you buy and mix gas like I do, that does not work. I buy super gas in 5 gallon containers, and add stabilizer at the gas station (keep it as fresh as possible!). I then pour the gas into one gallon containers and mix it with 2-stroke oil as needed. I have never had gas go bad on me this way, and I have stored it for up to 18 months with no problems. I use the StaBil red, and it works just fine. The StaBil green formula is intended for marine use or in high water conditions if you use ethanol blended gas. The only difference is the ability for StaBil green to absorb more water and to better keep phase separation from happening with ethanol. If you use 100% gasoline or if you are in a dry environment, then the phase separation issue is not going to be a problem.

BTW: this is rather complicated stuff. Phase separation happens when water is absorbed by the ethanol blended gas, and then the water and ethanol combine and separate out from the gasoline. Combined they become a layer at the bottom of the tank becasue the water is heavier than the gas is. Basic chemistry here: gasoline is made up from several hydrocarbons that are non-polar molecules. Water molecules are polarized (one side has a more positive change and one side has a more negative charge). For this reason water and gas do not mix. Ethanol molecules have both a polarized and a non-polarized side to them. Thus ethanol will blend with either non-polarized material like gasoline, or polarized material like water. Having a choice, ethanol is attracted to water more than gasoline, and so it will separate out from gasoline with water if any water gets into the ethanol blended gasoline.

As for OEM Stihl parts, I have to agree that the tolerances on Stihl parts (Mahle, etc.) are better than most aftermaket kits. For that reason I only use mostly OEM parts on my Stihl saws. Generally I can get new or slightly used engines from a buddy of mine that works in a Stihl shop up in WA state (if I buy a scored engine saw for cheap). I do use Cabre rings from a guy in Greece that sells them on Ebay. I am not sure if they are OEM or not, but they are good rings.

Good job on that tear down! I find the 210/230/250 saws a PITA to take apart, having done several of them myself. That is one fried piston you have there.

One suggestion, when you have everything apart, replace the crank seals. If you have an air leak it will ruin your nice new engine. Also it is a good idea to vacuum/pressure test after reassembly.

Another thing, many times a damaged looking cylinder can be refurbished by using muriatic acid to remove the stuck on aluminum. Both my Huskies ( purchased as non runners) looked pretty bad. They cleaned up nicely with some fine sandpaper sctochbrite and muriatic acid. I think the OEM piston kit for my 36 was less than $20.

www.arboristsite.com has a lot of great info for chainsaw rebuilding.
Here is a link to what I posted describing my Husky 350 rebuild.
http://www.arboristsite.com/chainsaw/100008.htm

Ok. The first issue. I cannot get the new piston into the new cylinder with the rings attach. I just won't fit. It fits fine if I take the rings off the piston. Any ideas. After reamitn the posts above, I am beginning to think I got the non Stilh aftermarket piece. Anyone have any ideas? I have come too far to quit now!

It wouldn't be the first time someone was sent the wrong rings, but can you describe the method you are using to stuff the piston in with those rings on it?

Oh, oh, oh. Very important note about rings on the pistons, you'll notice that the rings need to have their gaps right where the little pin looking thing sits in the piston otherwise they won't compress right.

Hi Don
did you try to install ring with out the piston into the cyl?
You should install the ring without the piston to measure the end gap of the ring,sometimes you need to file a little off the end to get enough clearance.To tight of end gap the piston could sieze when it gets warm.
Good Luck
Thomas

I did mine this Spring. Went from a 021 to a 250 as the saw body is the same. I did get a Stihl long block for $89.00 off of Ebay. It was what I would call a easy change over. The only bad part was getting one of the screws out of the block. Also changed the carb over to one that has the H and L adj. It seemed to really scream with the stock carb. Would do it again, as saved money and was fun to do.
Don

I've seen videos on YouTube showing how to get a chainsaw piston and ring into the cylinder. You might try searching there...

fantastic thread

I saw this and thought of bad gas for some reason....

Proper porting could have solved that problem

Always run with the spark arrestor screen in place! (Cue Smokey The Bear.....)