Egg shaped rim sprocket

[timberwolf]

I had noticed that the chain on my 260 seemed to have some what I had thought were tight spots in it. As I was cleaning the saw up last night, I checked the chain over closely and there did not seem to be any problem, so I tried another chain and found the same tight spot problem.

As I checked ito it further I figgured out that it was the original rim sprocket that was shaped like an egg. It was out of round by about 5-10 thousandths, I moved its position around on the spline, and checked the runout the high spot stayed consistantly in the same placed on the rim.

Have to pick up another sprocket next week.
Any one else see this before?

TW

 

[WRW]

Yup.

 

[jokers]

Hi Bill, how often have you seen oval sprockets before? All brands or just Stihl? I`ve never noticed one and now I`m wondering. Russ

 

[WRW]

Russ,
Someone where I work years ago started the idea that chains should be "banjo tight." That idea persists. When I took over the saw maintenance I found a few sprockets like that. Two Stihls and a Homelight. I rotated the rim sprockets and marked the cranks to see which was defective...the high spot was relative to the sprocket. I just adjusted the chain relative to the tightest spot on the sprockets and replaced them as I got the chance. Smoothed the chain travel right out.
The way I noticed it in the first place was running the chain along the bar by hand and noticing a slight drag at certain points in the chain travel. Haven't had any problems lately.

 

[fun_chopper]

Banjo tight?..(I have never touched a banjo!) define that please-Matt

 

[WRW]

Ha ha. Tight enough to ring like a banjo when you pluck it. You have heard one, haven't you?
I owe Russ an apology. I had another Stihl like that. After 9 chains on the same sprocket, it developed similar signs. An 025. Again, the new sprocket remedied the problem.
Motorcycle sprockets would do the same thing, so I never thought anything of it.

 

[jokers]

Hi Bill, thanks for the updated info on the 9th, but of course no apology is needed. I have a tendency to run my chains as loose as possible(not drooping but not snug) so I have probably had a few egg shaped sprockets and never noticed. Russ

 

[WRW]

That's how I like 'em...loose & lubed. The ones at work had sat for a considerable time with the chain so tight that you couldn't turn them by hand. That's why I was concerned about the crank condition.

 

[Crofter]

Jokers and WRW
Have seen somewhere that having your chain loose will cause bar rail chipping and chain chatter as it allows the tooth to rear back in the cut and pull the chain away from the bar. I am sure this is only when taken to the extreme, but where does it become a factor?. I go back to before roller noses were common so am not a fan of real tight chains either.

Frank

 

[treeclimber165]

For the last 5 years or so, I've pretty much used the 'dime' rule. Looking at the side of the bar- If I can fit a dime in between the tie straps and the bottom of the bar, I will stop and snug it up (and usually give it a 90 second tickle). But too tight is bad also. The chain cannot be tightened to the point that it causes drag when spinning it by hand. It's a fine line between too loose and too tight, but with a razor edge my chains don't need adjustment very often. If my chain needs adjustment, it usually means that I've hit metal or dirt somewhere.
I can see where someone cutting logs or firewood would not want to keep their chain as snug as I do. Fairly impractical considering the amount of dirt encountered when cutting on the ground.

 

[NevadaWalrus]

Not sure how correct it is. My shop only procedure is to tighten so the chain can be easily with light pressure be lifted just a little ( about 1/3 to 1/2") from the top without seeing movement on the bottom.

I've seen where some folks over tighten a hot chain when finished cutting, then as the chain cools and contracts it has bent the crank or damaged the bearings.

 

[WRW]

Frank,
I've not heard of loose chain causing what you describe. That's not to say that you are not right, but what you are describing sounds more to me like a depth guide problem. Steel is fairly elastic and will stretch and relax like a rubber band, so you can't eliminate the chain leaving the bar rails.
Russ said "not drooping". I took that to mean no clearance between the chain and bar. Brian's description of tightening was good also. Just remember to detension any chain that has been adjusted while it is warm from running.

Yeah, what Nevada Walrus said.

 

[Gypo Logger]

I find that worn sprockets and dull chain result in tensioning problems. The chain quickly becomes out of pitch, causing it to stretch. Then it becomes dry due to lube deprivation, because of the dull chain, then it shrinks, then it stretches as it gets lube in smaller cuts. Its the powdery bug dust of a dull chain that sucks the lube out of a chain. With the long, extended, hot cuts of a dull chain and worn sprocket, it isnt hard to fathom why a chain becomes quickly fook-ya-lated.
Gypo

 

[Crofter]

Gypo Logger


I can see by the ends of the timber in your pictures that you are having some problems!! They look like they were chopped off with the side of snowshoe!

Frank

 

[Gypo Logger]

Almost Frank, it was actually bucked thru with a frozen boot.
John

 

[Gypo Logger]

Hey Frank, here's another one I chopped in half with a frozen tobaggan.

 

[Crofter]

Beauty

Sure ain't the stuff you need to make cardboard. Yep you can tell a lot about a man by the stumps and sawchips he leaves behind. Also notice your skidder tires not all chewed to pieces.

Frank