056 that won't keep the chain on

[MikE2]

I have an old 056 with a 36" bar and I can't keep the chain on it. On smaller wood it works OK, but as soon as I start cutting through 30"+ wood the chain comes out of the rail on the bottom of the bar. Then I have to put the chain back on and make another cut and it does it again. I've tried it with the chain looser and tighter and it doesn't seem to make any difference. I've also tried it with new chains and it works better, but it will still come out but maybe on every 3rd cut. With the older chains its just about every time. It is an older bar but I rarley use it and visually I can't see much wear on it or the sprocket or anywhere else to cause a problem. It also doesn't matter if the bar is installed up side down or not. I've also tried instaling tha bar and tightening it down with the bar pushed up and then trying it with it pushed down and that doesn't matter either.
Any ideas?

 

[kevlar]

I would try a new bar, have seen bars that look ok but are worn and will not guide the chain properly-just my two cents.

 

[stihl 440]

+1

I would try a new bar, have seen bars that look ok but are worn and will not guide the chain properly-just my two cents.

Yep,+1.:greenchainsaw:

 

[Nuzzy]

I'm guessing bar too.

 

[Mad Professor]

0.58 bar and 0.50 chains? And/or bar groove is out of spec.

 

[weenieroaster]

With the chain repeatedly coming off like that when cutting, the drivers (part that engages the sprocket) must be getting buggered up too.

 

[MikE2]

I think I may have found the problem...
I put a new bar on and I noticed the rear stud was backing out as I loosened the nut. I thought I'd just tighten it after removing the bar, but now I see about a full turn of a helicoil has came out and bent out to where it was not allowing the bar to mate up flat against the surface. I removed the rear stud to fix that, and then removed the front stud too which was also loose and 5 or 6 threads of the helicoil came out with that and it was broken in to several pieces, along with the threads in the saw itself pretty much stripped out. Are these heli-colis factory or did someone already attempt a repair at this?

 

[blsnelling]

That is not factory. See if you can find Timeserts in that size. Much stronger.

 

[046]

my preference is to install a stepped stud. much stronger repair. puts stud back to original strength.

best way to avoid over tightening is to preload the bar. tighten bar until bar will move, but stay. preload by lifting bar up. then tighten bar down without over tightening.

rarely do I need to go over 20 ft lb, for bar to stay.

 

[blsnelling]

Does Stihl make an oversized stud to repair cases like this?