chain tension gets tight all by itself

[Nine6Teen]

after running the saw for a little bit, the chain got super tight all by itself, so much that the clutch started to slip.
I loosened the bar nut, loosened the chain tensionioning screw, and got the chain tension back to normal. re tightened the bar nut, started her up, and ran fine for a few minutes, then chain went taught again.

this time I removed the clutch cover, and inspected the chain tensioning device, when turning the screw, you can definitely see the mechanism work properly. also, the bar oil was working fine, plenty of oil, the sprocket and chain are relatively new, the bar itself is rather old, but the groove is clean. I cleaned the cover, and verified that the brake band and brake mechanism worked, so i put it back together, and this time the chain got tight even as I was tightening the bar nut using the standard practice of holding the bar up
what's going on ?
this is a 200 T

 

[Franny K]

Could you be pulling the bar forward some how like getting it stuck and pulling to free it? Re adjusting a bit for what happens when the bar nut is tightened isn't all that rare

the bar itself is rather old,
Grasp two points on the front bar sprocket and feel for play in that bearing. There are crank bearings and a clutch bearing as well.

 

[Big_Wood]

the bar is likely dropping as you cut. there is a support lug of some sorts to help support the bar as one bar stud would not do. make sure it is still there.

 

[Chainsaw Jim]

It's probably a roasted bar tip.
Also, can you show us a pic of your sprocket?

 

[turnkey4099]

It's probably a roasted bar tip.
Also, can you show us a pic of your sprocket?

As well as the nose sprocket. I had that problem once and it was traced to the nose sprocket.

Harry K

 

[Chainsaw Jim]

As well as the nose sprocket. I had that problem once and it was traced to the nose sprocket.

Harry K

Same thing

 

[HarleyT]

Let's see some pics!

 

[Wood Doctor]

As well as the nose sprocket. I had that problem once and it was traced to the nose sprocket.

Harry K

You guys amaze me. I almost said the same thing. I had it happen on my Echo CS-3900 about six years ago. Sprocket nose froze up. I added Moly grease and some oil, to it. That fixed everything. Never happened again and that's why I recommend greasing bars that have a lube hole on the tip.

My chain never got really tight by itself. It just plain started smoking from the heat and then tightened up and stopped dead. Probably the same ailment. The lube I added saved the bar.

 

[fearofpavement]

See if the chain loosens up when the saw cools down.

 

[bikemike]

Bar is probably shot and not enough oil so the bar heats up and expands. Or the cover is badly wore out and groved and not clamping the bar down evenly

 

[Hinerman]

You guys amaze me. I almost said the same thing. I had it happen on my Echo CS-3900 about six years ago. Sprocket nose froze up. I added Moly grease and some oil, to it. That fixed everything. Never happened again and that's why I recommend greasing bars that have a lube hole on the tip.

My chain never got really tight by itself. It just plain started smoking from the heat and then tightened up and stopped dead. Probably the same ailment. The lube I added saved the bar.

Call me stupid. How do you grease a sprocket? Thanks in advance.

 

[Bobosocky]

Call me stupid. How do you grease a sprocket? Thanks in advance.

Some bars have a hole in the nose that you can shoot grease into. AFAIK Stihl bars are all prepacked with grease and there is no way to add any.

 

[Hinerman]

Some bars have a hole in the nose that you can shoot grease into. AFAIK Stihl bars are all prepacked with grease and there is no way to add any.

AHA, my bars are almost all Stihl. Thanks

 

[HarleyT]

Call me stupid. How do you grease a sprocket? Thanks in advance.

First, you buy it a couple drinks........

 

[Hinerman]

First, you buy it a couple drinks........

Well played sir, well played indeed.

 

[Jeff Lary]

I had that happen a couple of years ago and discovered it was the chain adjustment/tensioner lug not lining up with the hole in the new bar. I had swapped out and old bar for brand new and no matter how I adjusted the chain after a few seconds the chain got way to tight.
Loooog story short the hole in my new bar for the adjustment lug to fit into,... was above the lugs position when I installed the brake cover. So I took the screw all the way out flipped the tensioner lug so it would line up with the hole and put it all back together and problem solved.

 

[Nine6Teen]

inspected everything, and noted that that plastic cover had several burnt areas, partially melted, plus it was missing a location stud. so my theory is that the plastic is deformed, weak, and not properly holding the bar down. If the bar comes off plane, it can loose its rotational fixation, thus allowing it to change alignment and work against the chain tension. so I replaced the cover with a brand new one. I'll take it out into the wood tomorrow for a test. Below are some pictures.

 

[MountainHigh]

First, you buy it a couple drinks........

That's a 5 out of 5

 

[mohick]

OH!! a one bar nut tinker toy DUH!!

 

[fearofpavement]

It's an MS200T. Not a tinker toy. Widely acclaimed to be one of the best top handled arborist saws ever.