What happened to my MS390?

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Getting ready to order some more parts for it later today.

Why order parts when you dont know whats wrong with it? If it was a clearance issue it wouldnt have gobs of compression and then none IMO. I once ordered a popup piston from lil red barn for my CE670, it didnt make over #110 compression. Replaced it with a Meteor that made #155. Both with no run time. Tear it down to id the problem if you can, then order the parts you need. Beleive me, I've ordered parts I thought I needed before id'ing the problem, only to have some parts leftover. If you're working on saws for a little spare cash, every penny counts. If you're not, well then maybe you can afford to do it that way.
 
Why order parts when you dont know whats wrong with it? If it was a clearance issue it wouldnt have gobs of compression and then none IMO. I once ordered a popup piston from lil red barn for my CE670, it didnt make over #110 compression. Replaced it with a Meteor that made #155. Both with no run time. Tear it down to id the problem if you can, then order the parts you need. Beleive me, I've ordered parts I thought I needed before id'ing the problem, only to have some parts leftover. If you're working on saws for a little spare cash, every penny counts. If you're not, well then maybe you can afford to do it that way.
I have a bunch of spare Stihl parts left over from other jobs, ordering another 390 kit is no big deal, I'll just use it on another 290 or 310 if I don't use it on this one. Sometimes I wish I was just doing one or two saws for spare cash, it would be a lot easier...
 
Now for the bad news: I put some oil in the spark plug hole followed by a small amount of fuel mix, pulled the rope and....it wouldn't budge! Thinking I may have hydro-locked the thing I took the starter cover off and tried to turn the flywheel by hand and it still wouldn't budge either way so the tear down began, quickest one I ever did. Turns out it had a busted piston, looked fine on exhaust side but back where the rings gap at the intake side the lower ring land was missing. It tore a big groove in the piston and the cylinder, rings and circlips were okay however. So like I said earlier I guess I'll order some parts tonight...
 
He'll give you pics of it if hes got one left.

I'll have to talk to the saw's owner about it before I try to buy one. I already told him the first one blew up and I could tell he was a bit disappointed. At any rate I'm not gonna buy another kit from the vendor that sold me the last one...In the meantime I guess I got a mess to clean up..
 
I didn't take any pics of the damage but mine was the ridge just above the piston pin below the bottom ring. I thought at first that one of the locating pins had come out but that wasn't the case. Looks like to me it was just a bad place in the casting that came off. It looks like yours got used a little before it let go, mine still looks brand new except for the damage..
 
The saw never ran.

I wouldn`t be surprised if it tossed a circlip and tore up the bore and piston, some times one can feel the damage done but others it does not seem that or feel that bad when pulling the engine over. I only had one engine brought to me that this had happened to and I could not tell exactly why the rings were hung up until I pulled it down, seen others where the ring broke upon startup. Neither saw ever got fixed as the owners refused to pay for good parts.

If it started then it ran, the only way you will know what happened to this engine is to tear it down, it won`t be fixed by members on here. We all like a guessing game from time to time but this thread is ,:thisthreadisworthlesswithoutpictures:
 
The saw never ran.
Depends on what you call ran. It started and ran long enough to choke out. If I had been faster I could have released the choke and it may or may not have continued to run. I took the choke off after it stopped and tried to start it again and it wouldn't hit and felt like low compression after that. It's back apart now, cleaning it up again...The circlips and the ring locating pins were both intact. Just looks like the casting broke...
 
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