Husky 365 Piston Skirt Rapid Disassembly - Potential Causes?

[hacskaroly]

I stopped by to let one of my co-workers know his Husky 575 should be ready to go tomorrow (which it is). I asked him what he was working on and he stated that he was running his 365 and it made a "bad" noise and would not start nor would it turn over, later it did free up, but had limited rotation range. Shaking the saw a little, I heard rattling in the muffler, I thought maybe part of the ring or a wrist pin clip. Got home and pulled the muffler and out popped a good sized chunk of the piston skirt. Pulling off the cylinder I found little bits of skirt pounded into the roof of the cylinder and many pieces settled down in the cylinder well (no wonder it would not turn, the crank was jamming up on the bits). What amazes me is that there is NO damage to the cylinder walls, I figured there would be scoring somewhere, but nothing, do these chunks end up shooting up the transfers?

Also, what causes the piston skirt to shatter like this? The crank does not have up/down play and the bearing is intact. After getting all of the chunks out, the crankshaft is spinning freely, no rough spots that I can feel. This is a work saw and the outside is embarrassingly dirty (at least I would be embarrassed to be a pro cutter with a saw this dirty). I am just trying to figure out what would have caused this. I cannot feel anything on the cylinder intake, exhaust or transfers which would have caught the skirt.

Pics are as follows:

 

[EFSM]

I would blame a worn piston skirt. The intake side is where the dirt and power stroke pressure are.

 

[hacskaroly]

I would blame a worn piston skirt. The intake side is where the dirt and power stroke pressure are.

Ok, I can see that, I suppose the small chip on the intake side broke off and then wreaked havoc on the exhaust side of the skirt.

 

[Junk Meister]

I Have bought 2 056 mag Stihls with the piston skirt mostly gone.
One of them was sent as a basket case. Saw was slightly dirty, cosmetics a 9 plus on a 10 scale. NO transfer on cylinder or piston (like your picture). Messaging the seller (the Bay) it was a family saw used to make a living doing maple sugar/honey/firewood and any job to make a buck. They ran a 20" bar and I got the opinion that they believed you ran it wide open with load or no load. I had requested they sent the old "Slug" but the shrapnel was not included. I Scotch brited the cylinder wall, A good cleaning. a used piston, new cabers from CCC, Base gskt. Mix, Bar oil. Ran great.

 

[hacskaroly]

I got the opinion that they believed you ran it wide open with load or no load.

This would make sense, the guys here like to test their saw in the morning...fire it up, gun it for about 15 seconds and shut it down. I think the guy was working on the saw, changing out something else, got it running and then gunned it (without load) to test it out. I can see how that could cause issues, especially with a piston that has been around for a while, who knows what cracks it might have already been in play due to the post repair "stress testing". I don't doubt that this saw will run well with a new piston, I think I saw an AM piston on Duke's for about $18.00. I have had good luck with Duke's pistons so far in other saws.