Chain Keeps Coming Off Chainsaw → Diagnosis

One of the most frustrating things that can happen when you own a chainsaw is having the blade fall off. The blade moves fast and it can be dangerous when it comes loose. There are a number of different things that can be happening to cause the blade to come off.

The most common reason that a chain keeps coming off a chainsaw is that the tensioner is too loose.

It is incredibly dangerous to work with a chainsaw that has a loose chain. If you are uncomfortable diagnosing why the chain keeps coming off, take it to a garden shop and have them fix it for you. No repair is worth your life.


You Should Know

  • Cutting bar– This is the part of the chainsaw with the blade spins around.
  • Sprocket– This is the part of the chainsaw that takes the power from the motor and transfers it to the blade.
  • Tensioner screw– This Screw allows for a loose blade to be tightened quickly.
  • Tension– You should never be able to pull the chain more than a half inch off of the saw at any time.


Chain Coming Off Diagnosis

The most common reason that a chain comes off as a lack of tension. This can be due to worn out bars worn out sprockets, a bad bar, or tension that is set wrong


1. Chain Tensioner

As you use your chainsaw, the chain will stretch. That’s why a chainsaw has the ability to adjust chain tension. There will be a screw on the side of the chainsaw. It will probably be labeled. If it isn’t, check the owners manual for the location.

A tensioner works by moving the bar away from the sprocket.

How to Fix

Tighten the tensioner until the chain is snug. Make sure that the screw for the tensioner is not stripped. If it is stripped, it won’t be able to keep the chain tight on the bar and the chain will jump again.

If the tensioner is not tightening the chain on the bar at all, it’s time to take a look and see if the tension gear is broken.


2. Guide Bar

The guide bar is the part of the chainsaw that the blade actually circles around. It can wear out. Or, more likely, it has bent.

When the bar rails wear out there isn’t as much groove for the chain to turn around.

How to Fix

Take the bar off and have a look at it on a flat surface, like a table or garage floor. Once you do so you’ll be able to see if it is bent rather easily. Inspect it for damage or anywhere that the teeth can jump off at. If it looks worn or bent go ahead and replace it.

It’s very likely that there is something wrong with the bar if the tensioner is tightening the chain adequately and the


3. Drive sprocket

A chainsaw uses a sprocket like the sprocket on a timing chain, or bicycle. Whether it’s through lots of use, or poor alignment The sprocket can wear out. If this happens, no matter what you do to get the chain back on it’ll be able to jump off that sprocket again.

How to Fix

Inspect the sprocket. Google the sprocket for your chainsaw and compare it to the one that is already on there. Are the teeth rounded compared to the one in the image? Is a tooth missing or loose? If so, that is all the evidence you need that the sprocket needs replaced.

The only way to fix this problem is to buy a new sprocket. Replacing one is not that challenging.


Tension Adjuster

The first thing that you would want to do is get the chain back on and make sure that the tensioner is set to the proper tension. There’s really not a whole lot to it. For just about every chainsaw, turning the screw clockwise will tighten it. Counterclockwise will loosen the blade.

You want no more than a half inch of slack when pulling the blade off of the bar. Refer to your owners manual for exactly how much they recommend.

When you get into trouble is when you tighten the tensioner as far as it will go. Once this happens you’ll have to assess what else could be going on with the chainsaw.



Repairing a chainsaw that has a chain that keeps coming off is a pretty easy task for someone who knows what they are doing, it can be incredibly dangerous for someone who does not. We recommend taking it in to be repaired if possible.