Hi all. A friend gave me a running MS280 which needed a new clutch and some clean-up. I got it apart and cleaned okay, but am having some trouble on re-assembly. It appears that the crank or piston is banging against something. It will move freely about a quarter turn then hits a hard stop. I removed the muffler and can see that it goes down far enough to see the first ring. I am new to chainsaw rebuilding, but familiar with other 2 stroke engine equipment. Any help on what I did wrong is appreciated. Thanks.