You noticed your riding mower isn’t giving you as nice of a cut as it once did. Your mower is cutting your lawn unevenly leaving strips of grass, a stair step type cut, or scalping your yard. You didn’t spend a bunch of money on a nice riding mower to only have your lawn look terrible after you mow.

A riding mower can begin cutting uneven when tire pressure is low; a blade is bent or installed incorrectly; the deck is not level; a bearing is bad in the spindle housings or pulleys; the blades or belt is worn; the engine speed is too low, or there is operator error.

Follow my list below for troubleshooting procedures so you can fix your riding mower’s cutting problem.

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Why Your Riding Mower Has an Uneven Cut

Riding Mower Blade is Worn or Dull

Dirt that is swirling in your mower deck can cause your mower blades to become worn and dull. The mower blade and deck are designed to create air movement and a suction under the deck to lift grass tall for a precise cut. Not only does it lift grass, but it also draws dirt under the deck.

This dirt wears the metal on your blade. With extreme wearing, strips of grass can be left when mowing the grass. There is no way to prevent wear from happening.

It is important to check, sharpen and replace your mower blades to maintain a good cut. You can find more information on sharpening your mower blades here.

Riding Mower Tire Pressures are Not Correct

Before continuing any further, you must check your tire pressure. Something as simple as a low tire can cause your mower deck to not sit level causing an uneven cut. Make sure the pressures are as shown on the tire side wall.

If you don’t verify you have the correct tire pressures before you move on to checking your mower deck for problems with your uneven cut, you could make unnecessary adjustments to your deck.

You will be creating more work for yourself when you must reverse the steps you took prior if you find the problem is actually your tire pressure.

Riding Mower Blade is Bent

A bent mower blade on your riding mower can cause your mower to give you a bad or uneven cut. When the blade impacts a solid object, like a tree root, rock, or toy, it can bend the blade.

Take time to walk your yard prior to mowing to minimize the potential of bending your mower blade.

Sometimes you will notice the impact and know to check for blade damage, while other times the impact may not be noticeable. When you notice it bad cut, it’s a good idea to check for a bent blade whether you remember hitting an object or you don’t.

You should check for spindle bearing damage when checking for a bent blade. You can find more information on checking your spindle housing in the next section.

Take safety precautions. Before you begin working on your mower deck, remove your ignition key and unplug your spark plug wires to prevent your mower from starting.

Always wear thick work gloves when working with your blades. There are two methods to check for blade damage:

Check for Bent Riding Mower Bladeby Removing the Blade:
Gain access to the bottom of your riding mower deck. Remove your mower deck if needed. Remove the blade and lay it on top of a new riding mower blade.

This is a good way to verify your blade is bent. If you find there are gaps between the old blade and the new blade, you must replace it with a new blade.  

Check for Bent Riding Mower BladeWithout Removing the Blade:
With your mower parked on a flat surface, measure one side of the blade from the ground to the blade tip and record the measurement.

Next, rotate the blade 180 degrees and measure the other side of the blade from the ground to the blade tip and record the measurement. If the two measurements are greater than a 1/8” difference, you must replace your mower blade.

Do not attempt to straighten a bent mower blade and reuse it. Doing so compromises the metal. The metal may crack and fly out of your mower at high speeds. This can put people or pets at risk of injury. It can also cause damage to structures.

Riding Mower Blades are Unbalanced or Installed Incorrectly

A riding mower can give a bad cut when the blade isn’t balanced or it is installed incorrectly with the wrong hardware or upside down.

Install with the sail pointing upward

When installing a riding mower blade, the sail needs to be facing upward toward your mower deck. The sail is the high side of the blade. When the blade is installed upside down, it will tear and bruise your grass. The sail can also dig into the ground causing spindle damage.

Some mower blades have a marking on them indicating the way a blade is to be installed. You may see “BOTTOM” or “THIS SIDE DOWN” stamped into the blade to assist you with installation.

If you don’t have writing on your blade, don’t worry. Just remember “Sail Up!” and you’ll install your blades correctly.

Use the correct hardware & install it in the correct order

Your riding mower blades need to be secured with the right hardware in the correct order. When the hardware is secured incorrectly, it can allow for movement in the blade giving you a bad cut.

Verify your blades are properly secured using the diagram in your owner’s manual or an online parts diagram.

Riding mower blades are balanced

A balanced mower blade is one where the weight is equal on each side of your blade. When it is not balanced, you will have movement when the blades are engaged. This can also cause spindle bearing damage and additional movement in the blade contributing to your uneven cut.

Your riding mower blades may become unbalanced due to unequal wearing of the blade. Another reason is when more metal is removed from one side of the blade than the other during the sharpening process.

You must ensure your blades are properly balanced prior to installing them on your mower. The best way to check for a balanced blade is with the use of a blade balancer. A balancer is an inexpensive tool that can prevent damage to your spindles and engine.

Another method to check a balanced blade is by hanging the blade on a nail that is mounted to your wall with the nail head sticking out of the wall about 3/4″ to 1″. You will need to remove metal from the end of the blade that is hanging lower until the blade sits level.

Riding Mower Deck is Plugged with Grass

When airflow isn’t able to move under your mower deck to create a suction that lifts your grass, your quality of cut will suffer. A mower deck that is plugged with dirt, grass, and other debris reduces that airflow.

It is important to scrape your mower deck periodically to keep it clean and free of debris. This extra debris collecting in your mower deck won’t only affect your cut quality, but it can affect the way your mower runs. A plugged riding mower deck will put your engine under additional load.

While there is no way to prevent buildup under your deck, there are ways to minimize this buildup including:

• Don’t cut wet grass: Wet grass is more likely to clump and stick to the bottom of your mower deck.
• Spray your deck with silicone of Teflon spray: Apply this spray to a clean dry mower deck. While this spray isn’t a miracle worker, it can reduce the amount of grass collecting under your deck. This should reduce how often you need to scrape the deck.

Riding Mower Deck is Not Level

A deck that doesn’t sit level will give you an uneven cut. Measure your deck from side-to-side to check for equal measurements.

The leveling procedures vary from one riding mower to another so it is best to refer to your owner’s manual for the correct procedures for your mower.

You will also want to check the rake. This is the measurement from front-to-rear. Some riding mower models require the measurements to be equal while others have the front of the deck sitting slightly lower than the rear.

Riding Mower Spindle is Bent or Spindle Bearing is Bad

A bent spindle or bad bearing in the spindle housing can cause your riding mower blades to give an uneven cut.

Check for damage to your spindle housings by grabbing ahold of each end of the mower blade. Rock the blade up and down. While doing so, listen for a knocking noise or any extra play (movement).

If you experience either one of these symptoms, you must disassemble your spindle housing and check for damage to the spindle or bearing. Make the necessary repairs.

Bad Mower Deck Belt or Pulleys on Your Riding Mower

A bad riding mower deck belt is a belt that is worn, stretched, cracked, or shredded. When you notice any of these conditions in your belt or your belt has a glazed appearance to it, it is time to replace your deck belt.

A worn deck belt can fail to grip your pulleys and spin them at high speeds. This can cause a bad mower cut.

After checking your belt, move on and check each pulley. A bad pulley is one where you feel resistance or hear noise when you slowly turn it by hand. This is an indication the bearing is going bad.

A pulley with a bad bearing will fail to sit level and parallel to the deck. A bad pulley can be the reason your riding mower is not cutting as it should.

Riding Engine Speed is Too Low

Your blade tip speed affects the quality you receive when cutting your lawn.  Your riding mower needs to be running at its top speed to give your deck enough power to rotate your blades at high speeds. Make sure your mower is running at full throttle when the deck is engaged.

You know your mower best. If you notice the power of your mower is not what it once was, have a small engine mechanic at your local small engine repair shop check it over.

Riding Mower Ground Speed is Too Fast

Adjust your ground speed to get a good cut. For your best cut, you need to operate your mower slower through areas of thick, tall, or wet grass.

Cutting through tougher conditions requires a slower speed to keep from overworking your engine. Moving too fast through your lawn can cause you to push over some grass instead of giving it a nice even cut.

Incorrect Overlapping Path with Your Riding Mower

You can cut down mowing time by spacing out your paths to get more grass cut in less time. This seems reasonable, but when your paths are too wide and not overlapped correctly, you can miss strips of grass leaving you with an uneven cut.

It may take a little practice to accurately figure out the right spacing for each path. Figuring out the right spacing will allow you to get the best cut while saving time.

Riding Mower Deck Shell is Damaged

The mower deck shell can become damaged when you accidentally hit an obstruction such as a fence post, tree, or building. A tweaked or damaged mower deck shell can be the cause of your bad cut and should be repaired or replaced.

If you are unable to repair your shell, check with your local riding mower dealership to get a price on a replacement shell and a complete deck assembly replacement.

Make sure you also get the cost of labor to swap the components of your deck to a new deck shell for an accurate cost comparison.

Your Lawn is Uneven

Running a wide format deck like a 48, 52” or 60” deck can scalp sections of your lawn when the ground is uneven. It is not able to bend with the dips in the yard so you end up with an uneven cut.

Using a push mower with a smaller deck will give you a better cut when mowing wavy areas of the lawn or ditches. The mower can also scalp your yard when you have high spots in your yard. To level out, these high spots use a weighted lawn roller to smooth out your lawn.