Let's play diagnose the farm boss chainsaw.

[Wood Doctor]

That piston likely was flawed from the start. It weakened further during use and flew apart. The small chunks of shrapnel bounced around and likely caused the top and bottom edge damage. You were running a cement mixer for awhile. You also have to wonder if the cylinder is worth keeping. How it could have survived without any damage inside would be rather amazing.

 

[fearofpavement]

Well, the cylinders are pretty hard compared to soft piston metal. From a cursory examination. The cylinder looks ok but would need to be cleaned up and examined in more detail. There isn't any transfer on the cylinder walls.

 

[dbittle]

Well, the cylinders are pretty hard compared to soft piston metal. From a cursory examination. The cylinder looks ok but would need to be cleaned up and examined in more detail. There isn't any transfer on the cylinder walls.

Nice work finding the problem. Well done.

 

[AKDoug]

Not to bust your chops, but this is why looking in the cylinder from both the intake and exhaust is on the Stihl engine check list. I doubt you will ever forget again

 

[VinceGU05]

It's on mine from now on [emoji106]

 

[fearofpavement]

Not to bust your chops, but this is why looking in the cylinder from both the intake and exhaust is on the Stihl engine check list. I doubt you will ever forget again

Well, as stated earlier in the thread, I did look at it from both sides but what I failed to do was rotate the engine while looking. If I had (or if the piston had happened to be in a different position) I would have noticed the damage.

I sent the saw down the road today with a local buyer. told him to run it and if he had any issues to bring it back. It's the first time I've sold a saw without thoroughly testing it... He got it for about $60 less than I would have sold it for otherwise. (Black Friday Special)
I handed him a chain file as well.

 

[AKDoug]

I learned my lesson in a similar fashion. A customer lost a 3/8" wide, by 1/4" tall chunk out of the intake side of the piston on a MS362. It took several tries to find the issue also.

 

[Wood Doctor]

I learned my lesson in a similar fashion. A customer lost a 3/8" wide, by 1/4" tall chunk out of the intake side of the piston on a MS362. It took several tries to find the issue also.

Agreed. When the piston/rings fail, most of the time you have to pull the piston from the jug to really ascertain what's going on. Inspecting the input side and the exhaust side from the openings works sometimes but certainly not all of the time.

In this case, the fact that compression remained with a piston this damaged is mind boggling.