chain wont stay on the gears

[joe_indi]

His saw has only one nut. No mistake there . I got this picture of the MS231 from the Stihl site.

[joe_indi]

It has a lateral chain tensioner, and I think the tensioner slide and the thread it moves on (part of the spur gear kit) might be damaged and would need replacement
(too many typo errors because I am using my Black Berry)

[Texas-Jim]

Ok if im understanding right the nut instead of loosening is turning the stud. Thats usually caused from over tightening the nut, remember they can fail above 16fbs. easiest way to get it off is simple to unscrew it, now it will remove the stud, once its off getting nut loose is easy when you can hold the stud. Inspect the threads, if they look damaged stihl offers a replacement stud with bigger threads that cuts new threads as it goes in. Put a drop of red locktite on it and your good.