You’re going up and down your lawn, just like you always do when you hear a funny sound. It’s almost like a “slapping” noise and it’s coming from your deck. You stop your mower to take a closer look. It turns out to be the belt – it’s loose and that’s what’s making the noise. You try to put some more tension on the belt, jump back on your mower and off you go again. A short while later the same thing happens, but this time it’s so loose that it’s come off the pulleys. You’re going to have to replace the belt.
This is actually pretty common if you have a riding or self-propel mower, particularly for landscaping contractors that use their mower A LOT. But if it’s the first time it has happened to you, you might be wondering…What Happened? Do lawn mower belts stretch??
Do Lawn Mower Belts Stretch?
Yes! Over time a lawn mower belt can stretch, although breakage is more common. When used for long enough, as it’s placed under tension, the belt may become elongated to the point that it’ll no longer stay in place when installed on the pulleys. Most belts are sold with a guideline with regard to the number of “hours of operation” that they will last for. Once lawn mower belts become stretched, the only option is to replace them.
Why Do Lawn Mower Belts Stretch?
You might be wondering whether there’s anything you could have done to stop your belt from stretching, so let’s look at the reasons why lawn mower belts stretch. There are a few things that come to mind here.
General Wear and Tear
Your lawn mower belt is placed under tension and is asked to work over and over again. There’s no break. It’s not taken off and “rested” like a player in the NFL or NBA. This will eventually take its toll, and in combination with some of the other factors I’m going to discuss below, means that the belt may eventually stretch, becoming slightly longer and no longer fitting correctly.
There’s no way to reverse this. This is especially true if you use your mower a lot. Mowing ½ an acre is not the same as being in charge of the maintenance of several acres.
Quality of the Belt
Is your lawn mower belt an OEM belt or a cheaper aftermarket brand belt? If you didn’t install the belt on your mower, you might not know the answer to this, but it can make a huge difference.
Poorer quality lawn mower belts (typically the cheap, aftermarket brands) are much more prone to stretching than a high-quality OEM belt (Original Equipment Manufacturer).
Age
This is less likely, but still worth mentioning. I say it’s less likely because a belt that’s very old is far more likely to crack and break than it is to stretch. But it is possible that over time, if season after season passes, that the belt will lose some of its elasticity and will not be able to retain its correct length.
How to Tell Your Lawn Mower Belt Has Become Stretched
Before you go ahead and head to the store to buy a replacement belt for your lawn mower, you want to be sure that a stretched belt is the source of your problems.
Have you seen any of these signs?
Unusual Noise Coming from Deck
As I mentioned in the intro, a strange noise is probably the first thing that you’ll notice if your belt has become stretched. This will usually either be a sort of slapping sound or it could also be quite a high-pitched squeaking sound too.
However, if you do hear an unusual noise and do find it’s being caused by the belt, it doesn’t necessarily mean it’s stretched. It could just have become loose and needs tightening again.
Won’t Stay on the Pulleys
If you increase the tension on your belt, make sure it’s properly seated on the pulleys, before starting to mow again and then have the same problem (belt coming off the pulleys) this is a fairly clear sign that the belt has become stretched and needs replacing.
It Could Also Be the “V” in the Belt Becoming Worn
When asking some friends about this problem a while ago, they told me about another alternative explanation that can give the impression that a lawn mower belt has become stretched, but in fact, it has not.
The sides (or the V) of the belt can get worn over time, and this results in them sitting a bit further inside the V-grooves of the pulley. This can make it look as though the entire belt has stretched, but in fact it hasn’t.
Final Thoughts
Lawn mower belts are far more likely to snap or break than they are to stretch given how tightly the cords in a belt are wound. But they can and do sometimes stretch, and when that happens will need replacing.
Hector Ramos says
Hi. I have a Murray self-propel lawn mower, the belt became loose (out of place) and since then I keep trying once I get it running to engage the self-propel but the belt comes out. Can you help me with this…
Guru says
Hi Hector,
This could be because of a couple of reasons. The belt being stretched out and old would be the initial issue I would look at. So, install the belt and check the tension to make sure that it’s not too tight or too loose. If the belt is not at the right tension, it can pop off either way.
Next, if tension is an issue, I would want to make sure that the tension spring is still in place and not stretched out. Sometimes when belts pop off, tension springs can become stretched and are no longer able to tension the belt correctly.
If the belt and spring seem to be ok, then I would have a look at the pulley to make sure nothing is loose or damaged. This will very easily make a belt fall off.
If you take a look in your manual you should find the exact belt tension needed for your lawn mower. You can check this tension setting using a belt tension gauge. I’ve seen gauges online for less than $20. They take all the guesswork out of the tension setting.
Thanks for your question.
Tom.