Chainsaw won't start when hot

[stuckmotor]

Except I didn't have a tractor at the time which left me little choice except get it sorted out. It also caused lots of frustration and took me a while to figure it out. I could mow about 15 minutes before it shut down.

I think mine ran about ten minutes and quit. This was in the 80's and inexpensive new coils weren't available. What I could get would have eaten up more than I wanted to gamble. I think I pulled one or two off of other mowers. They must have been bad too.

 

[4570Man]

I think mine ran about ten minutes and quit. This was in the 80's and inexpensive new coils weren't available. What I could get would have eaten up more than I wanted to gamble. I think I pulled one or two off of other mowers. They must have been bad too.

That's unlikely. You must have had a different problem.

 

[dfkrug]

I finally got time to fiddle with this some more, I pulled the muffler and
sure enough, the top of the piston is badly scored.

Do you mean the side of the piston, near the top?

Since you get good compression #s, your cylinder may still be OK. It is only worth fixing
if the labor is free and you can get a piston and ring really cheap. Sometimes only a ring
is necessary. That's $5.

It is amazing how hard the Nikasil surface of your cylinder is. You can take sandpaper to
it without making much of a mark.

 

[Oldpath05]

What will score a piston, bad, in a chainsaw, broken rings, straight gas maybe......

 

[crazyal]

Pull it apart and try to take some fine sandpaper to the cylinder. Most are coated with something like nikasil and are much harder than the piston. For my experience when you see scoring on the piston it means it got too hot and started to bind in the cylinder. Usually the exhaust port side of the piston gets it the worse. I was able to clean up a cylinder for a friend. Think I might have used water or WD40 to help. His cylinder looked real bad but it was all aluminum from the piston stuck on the cylinder. I'm sure if you search around on the net you can find someone who has plenty of experience cleaning them up, maybe even a youtube video. Otherwise break the saw down and sell the good parts on ebay.