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Chainsaw tensioner not working - missing part?


Tony P.'s Avatar
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10-06-16, 08:38 AM   #1  
Chainsaw tensioner not working - missing part?

I have a McCulloch MS1839 chainsaw. Recently, the tensioner screw failed to tighten the chain / move the bar. I removed the cover and noticed the tensioner wasn't moving when I turned the screw. Instead, the tensioner stayed stationary and moved along the screw as I turned it. Now I can't get it to move properly. I believe I'm missing some sort of clip or washer. However, the part is so small I can't find it (if it even exists) and doesn't show up on the schematic. Any idea what I'm missing, what it's called and where I can find it?


Last edited by Tony P.; 10-06-16 at 08:56 AM.
 
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marksr's Avatar
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10-06-16, 09:10 AM   #2  
I assume you've cleaned it all up and removed any sawdust/grime. Is the bar connected to the little tab that is part of the tensioner? There is a corresponding hole in the bar that the tab goes in to.


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10-06-16, 09:10 AM   #3  
What do you mean when you say the tensioner wasn't moving, then the tensioner stayed stationary and moved along the screw?

 
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10-06-16, 11:39 AM   #4  
Thanks for your quick comments. Here's more information:

"What do you mean when you say the tensioner wasn't moving, then the tensioner stayed stationary and moved along the screw?" Yes, the tensioner stayed stationary and moved along the screw.

"Is the bar connected to the little tab that is part of the tensioner? There is a corresponding hole in the bar that the tab goes in to." Correct, the tensioner is properly aligned with the hole in the bar.

So, when I put everything together the chain was OK but I wanted it tighter. As I turned the screw the tensioner (and the bar) stayed stationary. Thus, I am unable to adjust the tension.

There must be some part that forces the tensioner to move instead of just unscrewing but I don't know what that is.

 
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10-06-16, 11:44 AM   #5  
It's fairly simple. You basically have a odd looking nut with a tab on it that fits in a slot. The screw moves that nut back/forth in the slot. The tab connects it to the bar which will move as that nut does.


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10-06-16, 11:45 AM   #6  
Are saying the tensioner moves when you turn the screw, but it moves in the wrong direction? If that's the case the nut on the screw is stripped out and you need a new tensioner. That would usually have the screw and nut which has the nub that hooks into the bar hole to move the bar. Probably a factory part.

 
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10-06-16, 11:58 AM   #7  
Here's some more information:

"It's fairly simple. You basically have a odd looking nut with a tab on it that fits in a slot. The screw moves that nut back/forth in the slot. The tab connects it to the bar which will move as that nut does." Correct. That's how it should work if it was working properly - but it's not. Instead, the tensioner (odd looking nut) doesn't move and winds or unwinds on the screw.

"Are saying the tensioner moves when you turn the screw, but it moves in the wrong direction? If that's the case the nut on the screw is stripped out and you need a new tensioner. That would usually have the screw and nut which has the nub that hooks into the bar hole to move the bar. Probably a factory part." It does not move at all. It may very well be sufficiently stripped that it's not working properly. I'll look into that.

 
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10-06-16, 03:40 PM   #8  
You might try and push on it one way or the other and see if it catches and starts to move, likely just a small portion is stripped, probably from over tension on the chain.

At least 80% of the saws I see the chains are way too tight which wears many parts and heats things up. The chain need only be snug but loose enough that you can pull an 1/8 to 1/4 inch slack.


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10-06-16, 05:17 PM   #9  
I still can't figure out what the heck is happening. You say it's stationary and then say it's moving at the same time... that's contradicting. You said it winds and unwinds along the screw, which is what it's supposed to do. You turn the screw one way and it moves closer to the head of the screw, you turn it the other way and it moves closer to the end of the screw.

All I can figure is that maybe the clip on the end of the screw is missing and it's allowing the screw to back out and leave the tensioner in place instead of moving the tensioner along it's path.


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10-07-16, 06:27 AM   #10  
Chain Saw Chain Tension

The block on the tension screw is not engaging the bar. Remove the bar and chain from the saw . Loosen the tension screw all the way so that the block is all the way toward the rear of the saw. Install the bar and chain, making sure the tension block engages the bar and leave the bolt(s) attaching the bar loose so that the bar can be tensioned properly. Adjust the chain tension and tighten the bolts holding the bar.

 
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