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Author Topic: chain jumping off of long bar (42")  (Read 2883 times)

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Offline Dan_Shade

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chain jumping off of long bar (42")
« on: February 11, 2007, 12:20:30 PM »
I have a 42" bar that I bought to rig up a home brew "alaskan" jig for my 066.  The bar is a GB and the chain is Stihl non-safety chisel chain.

yesterday, I pulled out a ~30" white oak that was a storm blow over, so I started with my 24" bar, and cut the notch as far as the bar would reach, and started a plunge cut behind the notch.  I figured i'd get a regular chain and use the 42" bar to clean up the notch across the bottom and cut the rest of the bore so I wouldn't have to mess with getting it lined up working from both sides of the tree.

Anyways, I installed the long bar and chain, and forgot to stretch it, so when I started the cut, it tossed the chain right off...  so I took it all apart, and then stretched the chain running it for about a minute or so, and then retensioning.

I go back to the tree again, and as soon as I started cutting again, it tossed the chain again, this time it hit my chaps and ripped them open (that's why I wear them)...

So question is, what did I do wrong?  Are there any tricks to keeping the chain on long bars? 
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Offline beenthere

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Re: chain jumping off of long bar (42")
« Reply #1 on: February 11, 2007, 12:45:53 PM »
No tricks, other than the right chain/bar for each other, and the right tension, that I'm aware of.

Check for worn or torn up areas that were a result of the chain coming off. Alignment to the drive sprocket needs to be right. Could be a number of physical things, that cause the chain to come off.

I don't quite follow the "tree blown over"  and cutting a notch.  Same tree?

I'd a finished with the 24" bar, but suspect you wanted to try the long one.  No problem boring and not meeting up with the bore from the other side (as long as the hinge isn't comprimised (ruined)).  If the bore cuts are one above the other, there is no holding wood left to worry about.

south central Wisconsin
 It may be that my sole purpose in life is simply to serve as a warning to others

Offline Kevin

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Re: chain jumping off of long bar (42")
« Reply #2 on: February 11, 2007, 01:54:56 PM »
Dan;
I don't know how much experience you have so I'll ask if you raised the nose of the bar when adjusting the chain tension?

Offline Dan_Shade

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Re: chain jumping off of long bar (42")
« Reply #3 on: February 11, 2007, 02:07:34 PM »
I cut a wedge on the bottom side of the tree so that it will hinge over as the stump sets back down...

I did finish it with the 24" bar, I decided to cut my losses with the long bar. 

Kevin, I did pull up on the bar when tightening it (well, I had a helper pull it up, that's a long bar).

I'll check the alignment of everything, having a chain jump off is aggravating (to say the least), let alone dangerous.  Long bars are a bit more to handle anyway, I really don't like them!
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Offline Michael

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Re: chain jumping off of long bar (42")
« Reply #4 on: February 11, 2007, 05:58:26 PM »
I know this is basic stuff, but when I have problems it helps to make sure.
1. Measure the drive link for thickness. Should be .050, .058 or .063. Then measure the grove width to make sure it is exactly the same. Don't trust what is written on the bar. Worn or wallowed out spots on a bar that long will cause problems. Uneven rails will cause a problem also. Check out the drive links for damage since it has thrown it twice.
2, Check the drive sprocket for wear and the correct drive. Also check out the sprocket nose for side/side movement and wear. Most bars that long are .404. If you have 3/8 chain it will throw it every time.
3. Turn the oiler up all the way. That long bar needs all the oil you can provide.
4. This may be hard to do but try to keep the revs down a little until you have the bar started a little ways into the wood. A chain at full speed wants to makes a circle, not a flat retangular shape. This means the faster the speed the more the chain "grows" out of the bar at certain places. If you hit the wood at full speed while it is climbing out of the groove , because of centripetal force, it will want to jump.
If you need saws or parts I may be able to help.

Offline oldsaw

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Re: chain jumping off of long bar (42")
« Reply #5 on: February 11, 2007, 06:58:11 PM »
I've got an Oregon 42" and have run it on both my 3120 and 066 and never had any issues.  Ditto 36" bars from Stihl and Oregon.

Mark
So many trees, so little money, even less time.

Stihl 066, Husky 262, Husky 350 (warmed over), Homelite Super XL, Homelite 150A

Offline Al_Smith

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Re: chain jumping off of long bar (42")
« Reply #6 on: February 11, 2007, 07:33:46 PM »
Often times on a derail,you will bend or deform a drive link or two.
Most of the time you can find the culprit with a visual inspection of the chain.

If not,put the bar it a vice,install the chain and pull it around the bar by hand.If you have a bent driver,it should show up by this method.

You can straighten out a bent driver but if you are not confident in doing so,get another chain.You can always use the good portion of the chain for a shorter bar.

Offline Dan_Shade

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Re: chain jumping off of long bar (42")
« Reply #7 on: February 11, 2007, 09:29:07 PM »
a few notes, the bar is pretty new, it's in good shape, the sprocket tip is fine as well, it spins freely.  the drive sprocket doesn't show any wear, it's a .063 bar and chain.

I was cutting with the top side of the bar, and not the bottom side, would this add to the problem? 

i'll check out the chain and see if I have a bent link.  I had to file down a few drive links after it got tossed the first time.  I didn't bother to even look at it when it jumped off the second time.
Woodmizer LT40HDG25 / Stihl 066 alaskan
lots of dull bands and chains

There's a fine line between turning firewood into beautiful things and beautiful things into firewood.

Offline Al_Smith

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Re: chain jumping off of long bar (42")
« Reply #8 on: February 12, 2007, 04:18:54 AM »
I would think that running on the top may in fact be part of the problem.

It could probabley be argumenative but it would seem to me that the top would be like running a tracked vehicle in reverse.You are in essence pushing the cutters through the cut .It might sound silly but if one could see the action of a dozer track in action it would be more clear.

I have found that for  some reason running on the top seems to loosen things up a lot more that cutting on the bottom.This plus the fact you are likely running 140 some drivers  adds up to a lot of stretch.

On my longest bar,which is a 48" and seldom used,it took a number of adjustments before the initial stretch was out of the chain.

Offline ladylake

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Re: chain jumping off of long bar (42")
« Reply #9 on: February 12, 2007, 05:58:47 PM »
Like Al said, bent link.   Steve
Timberking B20 15000 hours +  Case75xt grapple + forks+8" snow bucket + dirt bucket   770 Oliver   Lots(too many) of chainsaws, Like the Echo saws and the Stihl and Husky     W5  Case loader   1  trailers  Wright sharpener     Suffolk  setter Volvo MCT125c skid loader

Offline Captain

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Re: chain jumping off of long bar (42")
« Reply #10 on: February 13, 2007, 09:05:45 AM »
You may find you want to run that on a 7 spline drive rim instead of an 8 spline also to slow it down a bit.

Cut with the bottom of the bar... as soon as you cut with the top, the bar drops and the chain loosens.  Cutting with the bottom of the bar also serves to tighten the chain between the bar and the drive rim during the cut, if you cut with the top of the bar with a long bar/chain, you tend to get chain stackup before the bar and the chain can come out of he groove.

Captain


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