Riding Mower Making Noise When Blades Are Engaged (Why + How to Fix)

Hearing a screeching sound or loud noise when you engage the blades on your riding mower is definitely not normal and something you shouldn’t ignore.

There are several potential reasons why your riding mower deck is making an irregular noise. The problem can be small and stem from something simple and harmless, or it can be a bigger problem that can lead to an expensive fix.

My best recommendation is to disengage the blades and figure out what is going on before it gets any worse.

Noise Coming From Riding Mower When Blades Are Engaged (The Short Explanation)

If your lawn mower has an unusual sound coming from the deck when you engage the blades, then it is most likely caused by an obstruction on top of the deck, something stuck in the underside of the deck, a damaged belt, or a problem with one of the pulleys.

4 Possible Explanations for a Riding Mower Making Noise When the Blades Are Engaged

If your lawn mower starts making abnormal noises when you engage the blades, it is a sign that something is wrong.

So, let’s take a closer look at some common causes and figure out the source of the screeching.

Something Caught Up in the Blades

It’s normal to pick things up with your lawn mower while you are out mowing the lawn. Palm fronds, kid’s toys, and even sticks will change the sound of your lawn mower if they get wrapped up in the blades.

There have been plenty of times I’ve mulched leaves with my mower and picked up big sticks. As a result, my usually quiet lawn mower starts to sound more like a helicopter.

So, park your riding mower, apply the brake, kill the engine, lift the cutting deck all the way up, and take a look underneath.

I wouldn’t be surprised if you picked something up and it’s causing an obstruction in the blades.

Something on Top of the Cutting Deck

The top of the deck is as much at risk of picking up hitchhikers as the underside. There are plenty of places trash can reach and then start to rub on the belt. Even the smallest thing can make a loud noise if it’s positioned just right.

So, lower your cutting deck as low as it can go so you can get good access to all of the deck, then have a good look around.

A place not to miss is the pulley guards. These are the perfect hiding places for rocks and sticks. If you can’t see into the guards, I’d recommend grabbing a wrench and removing whichever guards obstruct your view.

A Worn Out or Damaged Belt

A belt in good condition will normally just have a bit of a hum. If anything, you won’t hear the belt over the noise of the engine and the blades. But if you can hear the belt more clearly, then it could mean it is damaged.

If a chunk of the belt is missing or something similar, it can make a really bad thumping sound when you engage and run the blades.

If your mower belt isn’t tightened correctly, you could hear unusual noises and screeching as the loose belt wears out and becomes damaged.

So, stop your lawn mower and take a closer look at the belt.

Damage to a Belt Pulley

If your riding mower makes a loud, screeching noise when the blades are engaged, then it’s probably due to a bad pulley.

If a pulley isn’t maintained correctly or is damaged, you’ll hear the internal structure screech as metal rubs on metal.

Also, a bent pulley will drag on the belt and sound like a car with a slipping fan belt.

So, to check your pulleys, pop off the deck belt and give the pulleys a spin and a rattle. There should be little noise and no movement other than the spinning of the pulley.

If there’s an unusual sound or additional movement, you’ll have to carry out a repair.

How to Fix a Riding Lawn Mower That Makes Noise When the Blades Are Engaged

If you followed the steps above, then you should have figured out where and why your riding mower is making a noise when blades are engaged.

The next thing to do is figure out how to fix the problem. Let’s go over the steps, tools, and parts you’ll need.

Clearing the Underside of the Cutting Deck

Depending on what you have picked up with your lawn mower blades will determine how you approach this fix.

Anything that is just a little bit wedged should be easy to remove with some elbow grease.

But for anything that is really wrapped around the blades, like a rope, I suggest removing the blade using the same method you use to sharpen your blade.

Tools Required to Clear the Underside of the Deck

• Blade Removal Tools – Blade Brace & Socket Wrench

Clearing the Topside of the Cutting Deck

Anything stuck in the topside of the deck should be easy to spot, even if you have to remove the guards. But as a common practice, I make sure to clean the top of the deck after mowing.

If I’m washing my mower, I use a jet connector on my garden hose to blast out any trash. Otherwise, I use a leaf blower.

This is normally enough to prevent any debris build-up and keeps trash from getting too close to the pulleys and belts.

Tools Required to Clear the Topside of the Deck

• Screwdriver (Guard Removal)
• Hose Jet
• Leaf Blower

Replacing a Deck Belt

If your riding mower is making noise when blades are engaged, and you figured out that it’s down to a damaged belt, then, unfortunately, you’ll have to replace it.

I say unfortunately because belts can be on the expensive side, especially if you have to change them too often because of damage.

So, the first step is to remove the tension spring from the idler pulley. This will remove tension from the belt, so it’s loose and easy to work with.

Once you have removed the tension from the belt, you can pull the deck belt from the mower and set it to one side or just throw it in the trash.

Next, thread your new belt through the pulleys and reattach the tension spring. Just be sure to adjust the tension of the belt correctly.

Finally, to prolong the life of your belt, I suggest getting hold of a can of belt dressing. It will keep the belt supple and make it last much longer.

Tools Required to Replace a Deck Belt

• Replacement Deck Belt
• Spring Puller

Replacing a Deck Pulley

Replacing a pulley is basically only needed if the pulley is beyond saving. A lot of riding mowers have serviceable pulleys that can be greased, but not all of them.

So, if you have a riding mower making noise when blades are engaged, the pulleys might just need to be greased. But if you haven’t been greasing and one is worn, or it’s unserviceable, then you’ll need to swap it out.

So, the first thing to figure out is which part of the pulley is damaged. If the pulley makes a screeching noise, it means the spindle is damaged.

Here are the steps to change a riding mower’s spindle.

Adjust the Cutting Deck

If you are working on one of the outer pulleys, then you’ll probably have enough room to remove the pulley without removing the deck. But if you’re working on the inner pulleys, you might need to remove the deck completely.

So, adjust the deck to a level that makes it easiest for you to work on the pulley.

Remove the Deck Delt

Next, you’ll need to remove the deck belt. So, remove the tension spring from the idler pulley, then move the belt away from the pulley you’ll be working on.

Brace the Blade

To remove the spindle, you’ll need to brace the blade so that the spindle can’t spin. If you don’t have a proper blade brace, then you can use a piece of timber like a 4×2.

Remove the Top Nut & Pulley

Next, use a long-handled socket wrench to remove the top nut of the pulley, then lift it off the pulley.

Remove the Blade

With your blade brace still in place, remove the blade attached to the spindle you are working on and set it to one side.

Remove the Spindle

Now, use your socket wrench and remove all the bolts holding the spindle to the deck. Once you remove these bolts, you should be able to pull the old spindle from the deck.

Install the New Spindle

Next, grab your new spindle, and place it on the deck. Line up the bolt holes and install the bolts you previously removed.

Install the Blade & Pulley

Now that the new pulley is installed, you can reattach the top pulley and the blade.

I recommend that you take a look at your manual and double-check the torque specs of the blade and the torque of the top nut. You don’t want to have either part too loose or too tight.

Reinstall the Deck Belt

The final part of the pulley fix is to reinstall the deck belt. So, thread the belt back over the pulleys and reattach the tension spring. Again, be sure to adjust the belt tension correctly.

Tools Required to Replace a Deck Pulley

• Spring Pulley
• Blade Brace
• Socket Wrench
• Replacement Pulley