Last Updated on May 19, 2021

When Is It Time To Replace Your Lawn Mower Belt?

With summer underway and lush green blades of grass reaching for the sun, it’s time to get out your trusty lawn mower and groom the lawn for a level surface.

Like any machine with a combustion engine, lawnmowers require regular maintenance such as oiling, cleaning, and parts replacement. It’s recommended that you attend to any necessary maintenance your lawn mower needs before it becomes a bigger and more costly problem. Lawn mower belts are one of the components in your mower that you need to keep an eye on.

In this article, we’re going to talk about the signs of wear that indicate that your self-propelled lawn mower needs a belt replacement. 

Types Of Mowers

There are push reel mowers that don’t have motors to spin the blade. Their blades spin with the wheels when you push the mower over the grass. This type of mower requires physical force to get them to work and is best suited for small lawns.

Self-propelled mowers are powered by a small motor that cuts the grass and powers the drive system, which makes it move forward on its own without the need for manual pushing. This makes it ideal for mowing hills, plains, and large areas.

What Does A Lawn Mower Belt Do?

What Does A Lawn Mower Belt Do

To better understand what part your lawn mower belt plays in cutting grass, it’s important to understand your mower’s engine crankshaft configuration.

Once you pull the starter cord, the inlet valves which are connected to the camshaft release a fuel-air mixture. This mixture is compressed by the pistons’ compression stroke and lit by the spark plug, causing combustion. The shockwave from the combustion pushes the piston down and makes the crankshaft spin.

The tension springs on the valves control the opening and closing of the valve by pushing it back down after the combustion stroke. The crankshaft is connected to the camshaft via a drive belt to keep the machine spinning.

The lawnmower blades are also connected to the crankshaft via rear pulleys and a deck belt, so when the crankshaft is driven from the combustion strokes, the blades also start moving.

If all of this is too technical, the simple version is lawn mower belts link rotating shafts to channel the spinning force from the crankshaft to the mechanisms of the mower, i.e., the blades.

What Causes A Lawn Mowers Belt To Stretch?

Over time and use, lawn mower belts can elongate or even break in some cases. When this happens, it also loosens the drive belt’s grip on the pulley system rendering the mower inefficient or slow.

The main reason this happens is because of physical deterioration from prolonged use, which can be expected with any machine part. Most lawn mower belts are made from reinforced Kevlar. There’s no definite period over which stretching or damage can happen, but increased use means it will need replacing sooner.

Another reason for lawn mower belts stretching is the poor quality of material used in making the belt. The best way to avoid this is to compare the replacement belt to your original belt before buying it to ensure it’s the right belt for your machine. You can also buy another one from the original manufacturer.

How Do I Know If My Lawn Mower Belt Is Bad?

If your lawnmower is making a lot of noise, it might be a symptom of your belt’s loosening grip. It’s best to check on it before the belt breaks while being used, damaging the machinery. All it takes is a quick visual inspection to know if the lawnmower belt has reached its expiration and needs replacing.

Here are the signs to check for:

  • Smooth edges and evenness throughout the length are the ideal standards for lawn mower blades. If so much as a tiny portion is worn out or chipped away, that’s a potential hazard.
  • Examine the part of the belts in contact with the pulleys. If they seem glazed or burned, the belt needs replacing right away.
  • Shallow cracks tend to set in after months of use. If the belt appears brittle, it’s at high risk of breaking and should be replaced.

Adjusting The Tension

Replacement is one way of dealing with loose belts; another way is to adjust the tension. However, adjusting the tension won’t solve the problem if the belt is damaged. Adjustments only work in cases where the belt has come loose by accident or improper use, not physical deterioration.

The only way to tell if the belt needs adjusting or replacing is with a physical examination.

After that, adjusting the tension is simple. Inspect all the components of your mower deck. Your swingarm needs to be rotating freely. If it isn’t, try using oil. The cable that is connected to the lever is attached to a spring. The spring should be perfectly stretched but not loose. Problems in these components contribute to the loosening of the belt.

Next, tighten the belt with a cable adjustment and then check the new tension by testing the lawn mower on the grass again.

How To Replace Your Lawn Mower Belt?

Cracked Mower Belt

Replacing your lawn mower belt is an easy-to-learn skill and should only take a few hours. It’s a good idea to keep a spare belt or 2 on hand, so you don’t need to run out in the middle of the process.

Just remember to switch off the engine, set the apparatus down on a flat surface, and wait for it to cool if you’ve just used it before switching the belts.

  1. Disconnect the spark plug wire and switch off the ignition as a safety precaution.
  2. Remove the mower deck covers and disassemble the components to remove the drive belt from the engine pulley, which is connected to the crankshaft. Also, un-secure the belt fasteners.
  3. Disconnect the mower deck from the main body.
  4. Take the belt off of the pulleys you see in the mower deck and connect the new belts.
  5. Reassemble everything in reverse order and re-attach the mower deck to the main body. Remember to secure all the linkages using washers and retaining pins. You can now put the spark plug back in.

Check out this detailed video tutorial for a step-by-step breakdown of the process:

Before You Go

Replacing your mower belts before they snap will save you headaches and money. We recommend that you clean and inspect your lawn mower regularly to keep it in top condition.

As you clean it, inspect all the components to see if the belt may need changing. Also, if you’re replacing it at home, remember to refer to the manual provided by the manufacturer.

It may take some effort to learn how to replace the belt on your own at first, but it’s a chore that gets easier after you’ve done it once and is well worth it in the long run.


Author: Matt Hagens

Hi, I’m Matt the owner of Obsessed Lawn. I love to be outside working on my lawn, planning my next project. I created this website to help people like you find the best products for yard care and great advice. Learn more about me and find me on Facebook.