Constant chain jumping

[charles mann]

In previous 5yrs of owning my stihl 661, running a 36” bar for the most part, i havent until the past couple days, had an issue with my chain jumping the bar. I went from my 20”, to a 36” and 42” bar to buck a tree in to manageable sizes for loading. After install of the 20”, 36 and 42” bar, i would crank the saw, bump the throttle 4-5x then adjust the tension while still at an idle, till a had about 1/32” sag, from the chain link, to the bottom edge of the bar, then bump the throttle 4-5x more and readjust again if needed. The chain would jump track using all 3 bars. 

Is it as with bandsaw mills, the longer the bar/band, the tighter the tension needs to be? I wouldnt think with a 20”, i would have this issue, but i am. Again, i havent had this issue before, and i ran the 36” bar 90% of the time, unless i was in the tree limbing or just didnt want to put that counter weight bar on just to limb on the ground and would put on or keep installed, the 20” bar. 

Im running a factory oem stihl 36” bar, that came with the saw, an oregon 42” bar and county line (tractor supply co.) 20” bar, and all chains, im assuming are oregon, since that is the box the stihl dealer hands me with my new chain in it. 

Any help would be appreciated, bc this constant jumping is nerve racking. 

[doc henderson]

the drive sprocket might be a common thread to all three chains and bars so I would check that.  I assume you have always done this tension procedure.  I have been fooled with 36 inch to 60 inch b&c and thought is was tensioned, but then the bar sagged and the chain was loose.  good luck.

[Tacotodd]

Try MY personal procedure. Saw off, B/C installed obviously, turn engine assembly upside down & while holding the handle down to my truck tailgate but making sure the bar doesn’t touch anything turn adjustment screw in until you have what’s been described here as “no drag no sag”. That’s for a used chain but for a new chain just a tiny bit tighter (can’t give a specific amount what my description of tiny means because it depends on the bar length). I hope that helps. 

[Old Greenhorn]

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Any help would be appreciated, bc this constant jumping is nerve racking.

And time consuming and aggravating and sometimes even infuriating. 
Since you have the same issue on all 3 B/C combinations, as Doc suggested, it is not likely to be related to the chain or bar BUT when a chain gets thrown it often gets burrs on the drive links. I had this problem in the woods about a month ago and had to put the chain on the side until it could be fixed and replace that chain for the day. Feel the drive links on your chain(s) and make sure the chain rides freely in the bar ALL the way around and no links lift up in the bar slot or drag. Likewise check the nose sprockets for free turning ALL the way around. Nose pinches can be your original reason for the first chain jump and sometimes the bar get squeezed at the tip or punk wood can get between the side of the sprocket and side plate on the bar. If that's all good, then it is likely not mechanical.
 As for your tensioning process. I always hold the saw by the rear handle and rest the bar on it's tip to make sure the slop is taken out of the slots as I tension and tighten. In your case I am not suggesting this is the issue, just mentioning it for others. If the bar 'sags' when tightened it may slip up and loosen the chain during cutting and this frequently happens to newer users with single nut bars.
 As for the tensioning itself I tighten my chains with no droop at all. When I pull on the bottom of the chain mid-span on the bar it should stretch away, but snap back with a little click. The chain should roll freely when pulled over by hand. If it can't roll, it is too tight. If it has a little sag it is too loose. I am not an expert, hopefully one will weigh in here, but this is how I do it and has worked for me. The only time I have popped a chain is on those dang nose pinches with small branches and believe me, those drive links can take a beating when that happens.
 God luck.

[lxskllr]

You shouldn't have any sag at all with a properly tensioned sprocket nose, but 1/32" shouldn't be enough to cause it to derail. I'm a little skeptical of the rim being the cause, but Doc's right, it's a common denominator, and I can't think of much else that would persist across multiple bars.

FWIW, this is my chain installation procedure...

1: Install chain, install bar, chain in groove.
2: Put clutch cover on, turn nuts til they're on, just to keep the cover in place.
3: Tighten chain til it hits the bottom of the bar. Tighten clutch nuts til they're close, but loose enough to still run the chain tensioner.
4: Lift bar, and tighten chain til it hits the bottom of the bar again, then snug up the first clutch nut, but not fully tight. Check chain tension. It should lightly snap onto the bar, and not just lazily fall, but it shouldn't be a strain to pull it up either.
5: If that's good, I spin the chain by hand wearing a glove. Goto #4, and adjust again if slack was introduced.
6: Crank down clutch nuts, turn saw on, and rev a couple times. Good? If not, goto #4

[charles mann]

As for burrs and nicks, my only 42” chain, after jumping the 3rd time, did not want to ride in the groove on 4 drive teeth. I pulled the chain to put those in the drive sprocket, then worked the chain back and forth till it free spun several times around the bar. After that, it stayed in the groove and stayed on. I did take my saw wrench and cleaned the groove out, starting at the tip and working my way rearward. I did get lot of gunk, which is usual. I did check my nose sprocket for free movement, and it seems to move freely, no binding or dragging, but i also was using gloves bc everything was hotter than my hands wanted to hold on to for any length of time. 

Im thinking of getting a new drive sprocket, in .375, and .404, for a new 64” bar im looking at buying to make cookies out of part of this pecan i just cut down. I know i can make double cuts with my 36 or 42” bar, but id rather make 1 cut and have a csm helper handle on the tip for me to hold on to while someone else runs the powerhead. 

Does the clutch housing have to be changed when changing sprockets?

[lxskllr]

If you mean going from .375 to .404, no. You can switch to any pitch/gauge as long as the involved components match(bar, chain, drive sprocket).

[doc henderson]

after throwing a chain, the drive tang may be galled or scratched,  this can be knocked down with a file to the side of the tang.  It is prob. a result of being thrown not the cause, and should be fixed to not add wear to the bar groove, as that could then later add to the decline in bar and chain performance. 

[Real1shepherd]

There's usually at least a few drive teeth links that get mauled when the chain jumps ship.

I'd file down the sides of the mauled drive links and I had a round file that fit exactly the shape of the stock link. I'd put that shape back in even if the link wound up being shorter. You need that shape to shed debris.

Remember the order for floating sprockets;you can put a old chain on a new sprocket, but NEVER put a new chain on a well worn sprocket.

Kevin

[charles mann]

Well, put a new chain on the 20” bar, no issues, except for when the chain had to much slack and i wasnt paying attention and i got a kickback and the chain jumped track. Figured the jumping track was a sign to stop cutting and finish hand loading the small stuff. 

Put a new 36” chain on today, made 3 cleaning/freshening cuts before applying anchorseal and even with a tight chain, it jumped track when went to cut horizontal. Im bout ready to buy a new 36” bar and drive sprocket to see if that helps. 

[HemlockKing]

after throwing a chain, the drive tang may be galled or scratched,  this can be knocked down with a file to the side of the tang.  It is prob. a result of being thrown not the cause, and should be fixed to not add wear to the bar groove, as that could then later add to the decline in bar and chain performance.

Could be knocked down with a file
But if you’re down on time
Just toss it back on, fire up, WOT for a couple seconds, retighten chain, good to go   may need to adjust one more time too after a couple
Mind as the burrs melt down 

[Skeans1]

Well, put a new chain on the 20” bar, no issues, except for when the chain had to much slack and i wasnt paying attention and i got a kickback and the chain jumped track. Figured the jumping track was a sign to stop cutting and finish hand loading the small stuff.

Put a new 36” chain on today, made 3 cleaning/freshening cuts before applying anchorseal and even with a tight chain, it jumped track when went to cut horizontal. Im bout ready to buy a new 36” bar and drive sprocket to see if that helps.

Sight the bar like a rifle or place it on something flat, but I’m willing to bet it’s either the rim sprocket or the clutch bearing that are toast. One thing to remember with longer bars is you do need to keep up tension more so vs the short bars. When I’m running a 42 yes it’s tight for tension but nothing like a 60 is you really have to watch them then my 72 being a narrow style bar is 10x as bad as my fat belly 42 and 60.

[charles mann]

@Skeans1 

Thanks for that info. I was thinking more tension but wasnt sure and didnt want to over tension the saw. Ill take the bars to a local machine shop and have them trammel the 2 longer bars a d see if they might have a lil warp to them. 

[Skeans1]

@charles mann 
No need to take them to a machine shop find something flat and set them down if they wiggle they’re bent and easy to straighten. Another way to check straightness is to put then with the tip towards your eye and the heel of the up against something straight that’s vertical then sight the bar you’ll be able to see a very slight bend very easily.

[sawguy21]

Check the bar behind the sprocket and dress it the best you can.

[charles mann]

Check the bar behind the sprocket and dress it the best you can.

I did do that yesterday. There a very small lip on both side, since i flip my bar about every 3-4x of sharpening. 

[ehp]

First I got a stupid question. What pitch gear are you running with each chain
 By chance would you have a .375 gear and trying to run .404 chain  or the other way around . Next   no you donot need to run the chain real tight as that takes out the crank bearing on clutch side . You have no idea on how many crankcase I have seen where the crank bearing has spun in the case on clutch side because chain was always super tight by the owner. . Next and I have seen this a couple times. The bar Stud backs out from the crankcase . That causes that problem with chain jumping or chain oil not getting to the bar

[Raj]

I'm curious of the condition of the bar mount including clutch cover, studs and clutch drum.

[Al_Smith]

A number of things can cause a derail . Worn rim sprocket .Worn clutch drum the catches  the rim off center or causes it to tilt .It's one thing to flip a 20" but it would be a great concern to  me to flip a 36" .

[Al_Smith]

I might also add which most people already know a chain by it's design rocks in and out of the cut .It's not like a circular saw blade .Too tight it doesn't work like it should ,too loose it jumps the track .Madsens at one time and perhaps still might have  a little blub about this .Then a dull chain could cause problems pulling dust not nice big chips .Dust fills up the groove out pops the chain .