Stihl MS 251

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SteveB.

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I bought an ms 251 and for the first few hours it was great. Now it is repeatedly kicking the bar and chain. I went to the dealer and was too close to closing. I got 30 seconds of the tech's time and he said I probably bent the bar and should try putting on a new bar and chain. He also said the chain was too tight, but it was not actually seated properly when I handed it to him.

Long story short; I replaced the bar and chain and provided more play in the chain. It spins easily if I pull it when off. 42 2 minutes in the nut works loose and the bar and chain both point south. I know the nut is not on too loose as it is tightened down and does not move at all. I am a bit worried it will break the housing if I go tighter. Could it be the tree is too thick? It is an 18" bar and the tree is slightly thicker. Also the blade is not catching and is cutting free and easy through the tree.

Any thoughts would be appreciated.
 
Check to see if the stud is backing out of the housing too far. I once got a great deal on a new saw which had not been assembled correctly, and all I needed to do was bottom the bar stud against the casing (fully seating it). When it's out too far, the bar cannot be fully tightened against the casing.

As a side note, Stihl manufactures their homeowner grade saws not far from me in Virginia Beach, but the one I found with an improperly installed bar stud was a German-made MS150.
 
Bar nut should never come loose if tightened properly. You do not have to crank down on the bar nuts to keep them tight and they should stay tight.
It shouldn't matter how big the wood is. I have had and still do have many stihl's and I have never had a bar nut or bar issue.
 
That saw is "interestingly" designed. Bar studs thread into plastic chassis. Not for me, thanks.

Best put an eyeball on it often, if you're planning on keeping it.
 

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