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12 Reasons a Lawn Tractor Has a Bad or Uneven Cut

A new lawn tractor will give you a nice cut. A new mower deck, fresh blades, and new parts all allow for a great cut. After many hours of use, you may realize you are not getting the cut quality you once did. Your tractor may start to leave strips of grass, scalp your lawn and give you an uneven cut.

A lawn tractor gives a bad or uneven cut from a worn or bent blade; low tire pressure; clogged mower deck; unleveled deck; spindle or bearing damage; worn deck belt; too low of an engine speed; too fast of a ground speed; or damaged deck shell.

Before you begin performing any adjustments or repairs, take all safety precautions outlined in your owner’s manual. This includes removing the ignition key, disconnecting the spark plug wires, and setting the parking brake.

Cause for an Uneven CutSolution for an Uneven Cut
Worn mower bladeSharpen blade. Replace with the new blade when needed.
Low tire pressureCheck tire pressures and bring them to the correct level
Bent mower bladeReplace mower blade
Blade is incorrectly installedRemove and install with the blade sail point upward
Clogged mower deckScrape the deck
Deck is not levelLevel the deck from side-to-side & front-to-back
Damage to spindle or spindle housingReplace damaged spindle or housing
Bad deck belt or pulleysReplace worn belts and pulleys
Engine speed is too lowRun your lawn tractor at full throttle
Ground speed is too fastMow at the correct speeds for your mowing conditions
Incorrect mowing pathsOverlap paths so strips of uncut grass are not left
Deck shell is damagedRepair or replace your mower deck shell

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Follow all safety instructions provided in your equipment operator’s manual before 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.

Reasons Your Lawn Tractor Cuts Uneven

Tire Pressures

The first thing you need to check on your lawn tractor is the tire pressure. Something as simple as a low tire can cause your lawn tractor to give you a bad or uneven cut.

When a tire has less air in it, the side of the lawn tractor with the low tire will sit closer to the ground.

This makes the mower deck sit unevenly. Skipping this step may cause you to make unnecessary adjustments to the mower deck which you will have to reverse once you realize you have a tire pressure problem.

Check the tire pressures to make sure they are of equal pressure on each side of the lawn tractor. You will find the recommended tire pressure listed on the side of the tire sidewall. Fill your tires with air until they reach this level.

Worn or Dull Mower Blade

Dull or worn mower blades can beat up your grass and cause them to turn brown a couple of days after mowing. The ends of the blades can become so worn they are thin and rounded. This will leave strips of grass in between the blades.

Check your mower blades regularly and sharpen them when they are dull. On average, mower blades must be sharpened after about every 25 hours of use. They should be sharpened more frequently when using your lawn tractor in sandy or gravel-like conditions.

Blades can also become thin and wear the sail. The sail is the higher side of the blade responsible for creating air movement under the deck required to lift the grass tall for a nice even cut.

When your blades become extremely worn with rounded ends or the blade sail is thinner than the center of the blade, the blades must be replaced. Read more about inspecting, changing, and sharpening the blades on your lawn tractor here.

Blade is Bent

When the lawn tractor impacts a stationary object, the blade can bend causing an uneven cut. This can happen when the blade hits a tree root, rock, or some other hard object.

Impact with an object can also cause spindle damage. Be sure to check the spindle and housing if you find you have a bent mower blade.

Never attempt to straighten and reuse your mower blades. The integrity of the metal can be weakened increasing its likelihood to crack. This can be dangerous when it is spinning under your deck at high speeds.

There are two methods you can use to check for a bent blade on a lawn tractor:

Check for Bent Lawn Tractor Blade by Removing the Blade:
Gain access to the bottom of your lawn tractor deck. Remove the deck if needed. Remove the blade and lay it on top of a new 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 Lawn Tractor Blade Without Removing the Blade:
With your lawn tractor 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.

Mower Blades are Installed Incorrectly

I’ve had customers call telling me their new lawn tractor is cutting terribly. On many occasions, I have found the first time they installed new blades on the tractor was incorrectly performed.

The blades were put on upside down. Of course, placing blades upside down will cause a bad cut.

Install with the sail pointing upward
When blades are installed incorrectly with the sail facing downward, the blade is tearing and bruises your grass instead of giving it a nice precise cut. The sail can also hit the ground causing impact and damage to your spindle housings.

The high side of your mower blade, as known as the sail or fin, should be pointed upward toward your mower deck. Some mower blades are stamped with the word “BOTTOM” or “THIS SIDE DOWN” on the blade to indicate which side of the blade faces the ground.

If you don’t find markings on your blade, just remember “Sail Up” and you’ll install them correctly every time.

Use the correct hardware & install it in the correct order

Your mower blade may be secured by a bolt and washer; a nut and washer; or other combination of hardware. Refer to your owner’s manual or a parts diagram to make sure you are using the right hardware and placing them in the right order.

If the lawn tractor requires the use of a concave washer, make sure the cupped side is facing your mower blade.

Make sure the blades are balanced

Your mower blades must be balanced before they are installed on your lawn tractor. You don’t have to worry about balancing your blades when you are installing new mower blades.

You do have to ensure blades you have sharpened and are reusing have been balanced for a good cut.

A balanced blade is a blade where the weight is equal on both sides of the blade. If one side is heavier than the other, the metal must be shaved off the heavy side until both sides are of equal weight. The best way to verify you have a balanced blade is with a blade balancer.

A balancer is an inexpensive tool you should use to make sure you don’t cause additional damage to your lawn tractor deck and engine from the vibration caused by running unbalanced blades.

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.

Mower Deck is Plugged

A plugged mower deck will leave you with a bad cut. The mower deck is designed to use the air movement, created by the rotation of the blade, to form a suction under the deck. This suction lifts the grass while the blade passes by to evenly cut it.

When the deck is packed full of grass and other debris, the area available to create good airflow is reduced causing a bad cut with your mower. In addition to a bad cut, a plugged mower deck will cause your engine to work harder and possibly shut down.

Scrape your mower deck regularly using a deck scraper or wire brush. A putty knife will also work. Unfortunately, there isn’t any way to keep grass and dirt from collecting under the deck, but there are ways to minimize the amount that does collect.

  • Don’t cut wet grass: Wet or damp grass is more prone to clumping and collecting under the deck than dry grass.
  • Use a silicone or Teflon spray: Coat the underside of your mower deck to minimize the amount of grass that sticks. While this won’t keep all grass from sticking, it may reduce the amount of grass that sticks so you can scrape your deck less frequently.

Mower Deck is Not Level

The mower deck must be level from side to side. Depending on your model lawn tractor deck, the front of the deck may be required to sit even with the rear of the deck or it might sit slightly lower.

Refer to your owner’s manual for the measurement specifications and procedures to raise and lower the deck.

Spindle is Bent or Spindle Bearing is Bad

A bent spindle or bad bearing in the spindle housing can cause your mower blades to have excessive movement and leave you with a bad cut. To identify whether you have a problem, put on a pair of gloves and grab a hold of each end of the mower blade.

Rock the mower blade up and down. If you hear a knocking sound or feel movement, you are going to have to take apart your spindle housing to identify the problem. Replace any part in your spindle housing that has failed.

Bad Mower Deck Belt or Pulleys

A worn mower deck belt that is frayed, cracked, stretched, or has a glazed shiny appearance can slip on the pulleys.

It will fail to turn the blades at the fast speeds required for your lawn tractor to give you a nice quality cut. Replace a worn deck belt. If your belt keeps coming off check out this article for help.

Check the pulleys on the deck to make sure they are sitting securely in place and parallel to the deck. A bad pulley is one that doesn’t sit parallel to the deck.

Slowly spin each pulley feeling for any restrictions and listening for a noise coming from the bearing. If you experience this restriction or noise, it is best to replace the pulley.

You will be able to replace the bearing in some pulleys. Most idler pulleys have sealed bearings where you will need to replace the pulley assembly that includes the bearing.

Engine Speed is Too Low

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

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

Ground Speed is Too Fast

Know your mowing conditions and adjust your ground speed to achieve the best cut with your lawn tractor. Your engine will experience heavier loads when it is cutting through thick, tall, or wet grass.

You must adjust to these conditions and slow down so you don’t end up with a bad cut. Moving too fast through your grass can cause you to push over some of your grass and not give it a good cut.

Incorrect Overlapping Path

I have run short on time and tried to rush my mowing by spacing out my paths so I can cover more ground with fewer passes. When I was finished, I looked at the lawn and noticed strips of grass in the areas I missed. My paths were not properly overlapped.

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 the deck shell, check with your local lawn tractor 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 or You Need to Use a Small Format Mower

Areas on your lawn that are raised higher than the rest of the lawn can leave the scalping of the grass. In areas of my lawn, this is caused by molehills. In my case, I roll the lawn with a heavy roller to flatten the lawn.

Running a wide format deck like a 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.

Still Having Problems with Your Lawn Tractor?

You can encounter many different types of problems with your tractor as it ages. I have put together a guide to help you quickly identify the causes and solutions for the type of problem you are encountering.

I cover common problems like a lawn tractor not starting, smoking, cutting unevenly, vibrating, dying after running, and more.

Check out my guide: Common Lawn Tractor Problems & Solutions.

If you encounter a problem you don’t feel comfortable troubleshooting or repairing, contact your local lawn tractor dealership or repair shop for assistance.