Lawn Mower Blades Hitting Each Other? (Try This)

If your lawn mower is making a terrible sound from the blades hitting each other, then I’m pretty sure you have a deck with timed blades. Even though this is a very clever design, it does have its own unique set of flaws that require precise setup and maintenance. So, let’s get the lawn mower into your workshop and inspect what’s going on underneath.

Why Do My Lawn Mower Blades Keep Hitting Each Other? (The Short Answer)

Blades on a multi-blade deck that are coming into contact with each other in the cutting deck have not been aligned on the mounting bolts correctly, are not sitting on the alignment pins/mount, or the pulleys have become misaligned on the toothed deck belt.

A Closer Look at Why Your Mower Blades are Striking Each Other

There are two main types of setups for multi-blade cutting decks: offset and timed blades. The offset blade setup uses a staggered blade positioning so that a cutting overlap is created, and the blades can’t ever touch.

In contrast, a timed setup uses blades set to specific blade positions locked into place with a timing belt. As one blade points side to side, the other is positioned front to back. As the blades rotate, the timing positions keep them in their specific orientation and maintain this spacing distance.

So, let’s see why your mower blades are hitting each other and what has gone wrong with the timing.

Incorrectly Mounted Blades

One thing that timed blades have in common is that their blades lock onto the deck spindles. This is so that if the blade mounting bolt becomes a little loose, the blades can’t turn out of position and end up coming into contact with each other.

Lawn mowers, like the Cub Cadet LT lawn tractor, use a 5-point blade mount, whereas the Toro Timemaster walk-behind uses a two-pin washer to ensure the blades are positioned correctly.

Now, if you forget to install the two-pin washer on your Toro Timemaster, there will be nothing to keep the blades correctly timed. Also, if you don’t position the blades on the Cub Cadet correctly, the blades will end up striking each other.

So, take a look under the deck and inspect the blade mounting position and hardware. For Toro mowers, you want to make sure the washers are in place. If one or two are missing, then this is likely to be the reason your mower blades are hitting each other.

For the Cub Cadet, you need to turn one blade so that it faces side to side in the deck, then check the other blade’s position. If it’s not front to back, the alignment is out. The difference between the two designs is that the Toro blade only has one position, and the Cub Cadet has five due to the five-point star mount.

So, if the Toro blades are mounted correctly, you’ll have to look elsewhere for a problem, whereas the Cub Cadet design allows you to adjust the blade even if something is off with the pulleys or timing belt.

Incorrect Alignment of the Pulleys

When toothed belts are in good condition and tensioned correctly, they do a very good job of keeping the lawn mower blades in sync. Unfortunately, like any belt on a lawn mower, over time, they become old and less effective at doing their job.

When this happens, the teeth on the belts can wear down and stretch out. As a result, even though your blades may be installed correctly, the belt could slip and cause the timing to go out of sync.

So, take a look at the belt and make sure that there isn’t any sign of damage and that the teeth haven’t worn down so much that they’re no longer doing their job. If the belt does look worn, damaged, or loose, you’ll need to install a replacement or check the tensioner.

How to Stop Mower Blades from Hitting Each Other (2 Things to Try) 

When carrying out any repair because the lawn mower blades are hitting each other, I like to start at the top and begin with the belt/pulleys and then move on to the blades. Then I always go back and check the timing of the whole system. This is because one repair can affect another. So, let’s start with the belt and pulleys.

Replacing a Cutting Deck Timing Belt

If you discover that your timing belt is to blame for your lawn mower blades hitting each other, then you want to remove it and replace it with a new belt. These are the typical steps to replace a timing blade belt on a Toro Timemaster, which is very similar to other sync belt systems.

1. Remove the spark plug cable and tuck it out of the way.
2. Remove the drive belt guard mounting bolts from the blade/drive pulley.
3. Remove the drive belt guard from the lawn mower.
4. Remove the drive belt from the blade/drive pulley.
5. Engage the blade engagement lever on the handlebar to disengage the blade brake.
6. Loosen off the belt tension plate.
7. Remove the old blade belt.
8. Tilt over the lawn mower.
9. Position one blade side to side.
10. Position the second blade back to front.
11. Feed the new blade belt onto the pulleys.
12. Check that the blades are still synced in the correct position. If they are not, then remove the belt and repeat the process.
13. Re-tension the tensioner plate to the manufacturer’s recommended tension setting.
14. Turn the blades by hand and check that the blades rotate without coming into contact with each other.
15. Position the lawn mower in an upright position.
16. Install the drive belt.
17. Release the blade brake.
18. Replace the belt guard and bolts.
19. Install the spark plug cable.

Tools to Install Toothed Belt on Synced Blade Systems

• Socket Wrench
• Clamp to Help Hold the Handlebar Lever In Place

Now, if your riding lawn mower blades are hitting each other and flipping it over isn’t an option, then there are a few other ways to go about fixing it. The first is to remove the deck completely, or if you have a mower like the Cub Cadet, you can use the pulley markers.

If you take a close look at the blade pulleys, you’ll see some arrows showing you which way the blades are pointing. So, as long as you have the arrows pointing 90 degrees away from each other, you should be good.

Installing Timed Blades Correctly

If you have a riding lawn mower like the Cub Cadet and you just relied on the pulley markers to sync the pulleys, then you still need to check the blades. This is because the star pattern allows you to install the blades in five different positions.

So, just because the pulleys are right doesn’t mean the blades are. Now, if you tilted your mower over during the belt replacement, you should be good. But it’s still important to make sure the blades are actually installed correctly so that you don’t run into any problems. So, let’s go over these two different blade types.

Tools to Install Blades on Synced Blade Systems

• Socket Wrench
• Blade Brace
• Clamp to Help Hold the Handlebar Lever In Place

Toro Timemaster Push Mower Timed Blade Pin Design

1. Position the pin washer onto the blade spindle so that the tabs point up to the spindle and the pins face downwards.
2. Twist the washer, so it locks into the spindle.
3. Position the blade onto the wash, ensuring the pins are located in the blade pin-holes.
4. Install the blade bolt.
5. Tighten the bolt to the recommended torque.
6. Confirm that both the tabs and pins are seated correctly.
7. Repeat the process for the second blade.
8. Disengage the blade brake.
9. Rotate the blades by hand and check the blades are synced correctly.

Cub Cadet Lawn Tractor Timed Blade Star Design

1. Align the pulley markers to the correct positions.
2. Position the first blade onto its blade pulley mounting position, matching the direction of the pulley marker.
3. Install the blade bolt.
4. Tighten the bolt to the recommended torque.
5. Position the second blade onto its blade pulley mounting position, matching the direction of the pulley marker.
6. Install the blade bolt.
7. Tighten the bolt to the recommended torque.
8. Disengage the blade brake.
9. Rotate the blades by hand and check the blades are synced correctly.

Why It’s Important to Fix Your Troublesome Blades ASAP

If you can hear the awful sound of your blades hitting each other, then you’re definitely going to want to change your cutting blades. Usually, you’ll find that they are damaged beyond any useful state. Even if you resync the blades again, you’ll still notice the symptoms of blade damage and unbalanced blades. So, they are not going to cut very well at all.

Before letting the blades get too far out of sync, you should be aware that damage is being done elsewhere with every spin of the blade. Here are a few problems you might encounter.

• Pulley & Bearing Damage
• Belt Damage
• Tensioner Damage
• Excessive Vibration Leading to Various Mower Issues
• Mower Deck Issues
• Stress on the Driveshaft and Engine
• Lawn Damage

I hope this article answers your question of “why are my mower blades hitting each other?” And if you follow my tips, you’ll have your lawn mower back in sync in no time.