Sthil MS250 - Chain Loose then Tight - Won't Run

[StacksCT]

I have Stihl MS250 that has run well for years. After noodling some big oak rounds into halves, it will no longer run (occasionally will start, but not run for more than 3-5 seconds). As I pull the chain around the bar, it is very loose, then very tight. I figured that I bent something and needed a repair. The local Stihl dealer diagnosed a stretched chain, sold me a new one, and said everything would be fine. However, I am still having the same problem. Thoughts?

 

[Fifelaker]

Worn sprocket.

 

[Giles]

I have Stihl MS250 that has run well for years. After noodling some big oak rounds into halves, it will no longer run (occasionally will start, but not run for more than 3-5 seconds). As I pull the chain around the bar, it is very loose, then very tight. I figured that I bent something and needed a repair. The local Stihl dealer diagnosed a stretched chain, sold me a new one, and said everything would be fine. However, I am still having the same problem. Thoughts?

The way I see it, it has to be one of three things---
Bad bar nose sprocket/bearing
Bad drive sprocket/bearing
Bent crankshaft
You should be able to easily check all these things .
By the way- I always buy American when possible. Some time ago, I ran into the exact same problem you are having after replacing a drive sprocket.
Sad thing is, I bought a HERR sprocket because it was made in USA! Sprocket was welded about 1/32 of an inch out of round with clutch drum!!
It went into my scrap pile!

 

[Clarkbug]

I also would go with a worn sprocket and/or bearing. Wouldn't hurt to check the sprocket nose in your bar either as Giles mentioned.

 

[Clyde S. Dale]

Find a new dealer.

 

[TreePointer]

Find a new dealer.

Agreed!

Stihl chain isn't known for stretching and a quick inspection of your saw setup should have resulted in an accurate diagnosis of the problem. Around here, the old Mom & Pop dealers are much better at this than then John Deere and other new shops.

 

[Captain Hornet]

My MS250 has been a beautiful trouble free saw, On yours, what would happen if you tried to start it with the chain off. That would tell you pretty quick if the carb, ignition, and the rest of the saw is okay. David