My two bits, use red scotchbrite to clean up the jug and buy a meteor or oem piston. I had a 3120 hit my bench that ran good, I peeked at the piston and it was a bit scored, long story short the saw had an a/m top end, a few air leaks, and a bunch of clear silicone everywhere. I tore it down, redid the bearings, seals, and gaskets with oem parts, bought a new oem top end out of Canada (~$400), and put it together and sold it. Did it run okay before I started? Yes. Was it still fubared? Yes. Am I happy I did a quality repair job before I sent it on to its new owner? Also yes.
While
@rogue60 was a little harsh, I'd tend to agree with him. If you can afford to half-ass something multiple times you can afford to fix it correctly once. If you can't afford to fix it correctly either save it till you can or pass it along to someone who can. I'm pretty sure the cylinder that got pulled off the 3120 I rebuilt could have been cleaned up and I would have only spent $50-$100 on a piston instead of $400 on a complete top end. But, the repair guy tossed it and put on poor performing Chinese crap before he sold the saw to an unsuspecting guy.
Lastly,
@PP4218 Stihl typically does not make their p/c sets. They're either Gilardoni (Italian), Mahle (Germany w/a base in Brazil), or KolbenSchmidt (German). I believe the Chinese Stihl plant makes MS170's, MS250's, and the like, and they're still monitored by people who give a crap. The $40 deluxe p/c sets are made by 5 year olds who's bosses don't give a crap about the quality of their products provided the $ keeps rolling in. While this sounds kinda harsh, I'm just telling you the honest truth as best as I can. What you do is up to you, but I'd go for a Meteor piston personally.
lol
