Do Lawn Mower Belts Stretch? (Revealed)

Man pushing mower

The drive belt is an important part of any mower and when issues arise with the belt, it can spell problems for the mower.

In this article we will dig deeper into the question: do lawn mower belts stretch? And also look at what can cause a mower belt to stretch as well as how long you can reasonably expect your lawn mower belt to last.

So without further ado, let’s get started.

Do Lawn Mower Belts Stretch?

Yes lawn mower drive belts do stretch, and when this happens they often will not sit on the pulleys as effectively. The result will be your mower will lose speed and cutting efficiency. Often the cause is just simply excessive usage over time and the solution is simply to get the belt replaced.

Why Do Lawn Mower Belts Stretch

Although it might not be obvious to you and me (unless you are mechanically minded), lawn mower belts do stretch.

If you are asking how much do lawn mower belts stretch, it is a minimal amount, often a quarter of an inch or less.

But the basic fact is, over time, the belt can elongate due to the tension it is under and even a small amount can affect the mower. 

However most mowers have a spring-loaded belt tensioner device built in that will keep a stretched belt tight enough to allow it to work ok.

For this reason, it is more common for a belt to snap completely before it becomes obvious it is streched.

There are a few things that will cause a lawn mower belt to stretch:

Reason #1: Wear and Tear

As is the case with most things mechanical, the longer and more often you use it the higher the likelihood of something going wrong.

With lawn mower belts often the “V” area of the belt wears down and the belt then rides deeper into the pulleys, which creates excessive length and causes the belt to slip.

Effectively the belt loses its grip on the pulleys in this scenario.

With plenty of use, other parts of the mower will naturally wear more as well.

If parts such as the bearings, brackets and arms wear down sufficiently that can cause alignment problems for the belt as well.

Even a new belt will struggle with worn parts, so check both the belt and the parts to see where the problem lies.

Reason #2: A Problem With the Pulleys

We have already established from the point above that lawn mower belts work in conjunction with a system of pulleys to function efficiently.

If something has upset the equilibrium of the pulley system and it is misaligned, you will find the belt will be thrown off it much more easily.

What could cause the pulley system to be misaligned?

Well often it is accidentally striking something like a concrete sidewalk or curb when the blade is running at full throttle.

This can quite easily bend a spindle, and cause the belt not to run efficiently.

A telltale sign is a belt that has fraying on one side or a pulley that is particularly worn on one side in comparison to the other.

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Fixing an issue like this depends upon the severity of the problem, often simply buying a new bolt or spindle will be enough. 

If the damage stretches further and the deck is misshapen, then a trip to an expert might be in order!

Again no matter how well you look after your mower and avoid striking any hard objects, the pulleys will gradually wear over time and need replacing.

Reason #3: The Deck Is Bent

Lawn Mower viewed from above

In the scenario mentioned above, it is important you determine whether it is just the bolt/spindle that is bent or if it is the actual deck.

If the deck itself is bent, then buying a new bolt or spindle will make no difference as it will still not be perpendicular due to the damaged deck.

This is more difficult to fix as you will probably need to remove the deck and all the parts mounted on it.

You will then need to find a way of straightening out the metal around the hole where you mounted the bolt/spindle before putting it all back together again and reinstalling it.

In this case I would definitely consult an expert!

Reason #4: The Belt Tensioner is Not Working Properly

Right back at the start of this article, I mentioned that most mowers have spring-loaded belt tensioner device that’s job is to keep a belt stretched tight enough to work without a problem.

If that tensioner gets stuck, or something is causing it to not work properly then it will mean the belt loosens too much (or sometimes it can pull it too tight).

Check the tensioner to see if it is working properly, often there are multiple holes you can use to adjust it.

Reason #5: You Are Stressing the Belt Out!

One simple hack that will reduce the likelihood of multiple parts of your mower being stressed out unduly is to throttle down before you engage the blades.

If you have the engine running at full speed and then hit the blade clutch it puts a lot of pressure on all of the components as the power works its way down to the drive path to the blades.

All you need to do is let the engine idle, then engage and hit the throttle for the blades and start mowing.

This will put a lot less stress on all parts of the mower.

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Reason #6: The Belt Might Not Be On Correctly in the First Place

The most common mistake to make, and the easiest to fix is to make sure the belt is fitted correctly in the first place.

It is easy to have the belt the wrong way around, which will reduce grip and tension.

Read your owner’s manual which should help you make sure the belt is routed correctly, and also tell you when it needs to be replaced.

What Happens When A Lawn Mower Belt is Stretched?

In short, your mower will be nowhere near as efficient and the quality of the cut will be severely affected.

A stretched belt will slip more, resulting in a loss of power and more strain on the engine.

Mowing your lawn will take much longer and it will be an incredibly frustrating process.

How Long Do Lawn Mower Belts Last?

This really is a bit like asking how long is a piece of string?

It is dependent upon the quality of the belt in the original mower, how well you look after the mower, what type of lawn mower you have, the size of your lawn and of course how much use it sees.

In my experience, I need to replace the belts on my mower around every two to three years.

Your owner’s manual should indicate how long you can expect your belt to last.

But rather than relying on an arbitrary figure, if you start to feel your mower decreasing in ground speed and losing its cutting efficiency it could be time to replace the belt.

How to Tighten a Lawn Mower Belt

Again this depends on the belt and the make and model of your mower.

Probably the quickest and easiest way is to simply do a YouTube search and you will probably find a video walking you through the process.

Usually, it will be a case of identifying the pulley arm and the adjustment bolt.

Loosen the bolt and press against the arm and pulley and tighten the nut and bolt of the pulley arm. The process is usually a lot easier if you have someone alongside you helping you.

When you put the belt on make sure it is not so tight there is no deflection at all.

But you are best off consulting the manual or YouTube, which seems to cover everything these days!

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Final Thoughts

Do Lawn Mower Belts Stretch infographic

Yes lawn mower belts do stretch, as shown by the infographic above.

Often it is not enough to be visibly noticeable, but enough to be noticeable by the effect it has on your mower, which will run slower and not cut as well as a result.

Usually, it is simply down to wear and tear on either the belt or other parts of your mower.

Belts are fairly cheap, around $25 or so for a new one, and fairly easy to install with the help of the owner’s manual or YouTube!

You should probably factor in replacing the belt every three years or 100 to 150 hours or so, and once that is done your mower should be running like new again.

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