13 Reasons Your Zero Turn Lawn Mower is Cutting Uneven

Have you ever finished mowing and turned to admire your lawn only to find it looks terrible? You invested quite a bit of money to purchase a zero-turn lawn mower to get that well-manicured lawn. It is highly frustrating to find your mower is no longer giving you a nice cut and now it looks bad.

A zero-turn lawn mower can provide an uneven cut when the tire pressure is low; the bearings are bad in the pulleys or spindle housings; the mower deck is plugged with debris; or the mower blades are dull, bent, or unbalanced. The zero-turn mower’s speed and mowing conditions can also cause an uneven cut.

I have listed below a complete list of items that can cause your lawn mower to cut unevenly providing for a bad cut. Take safety precautions before working on your mower deck.

This includes removing your spark plug boots and the ignition key. Protect your hands from your sharp blades. Refer to your owner’s manual for additional safety tips for your zero-turn model.

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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 Zero Turn Mower Gives You an Uneven Cut

Low Tire Pressure on Your Zero Turn

Before you begin checking anything on your zero-turn, check your tire pressures. Something as simple as a low tire can throw off the level of your mower deck and give you an uneven cut.

A low tire can cause the side of the deck with the low tire to sit closer to the ground making the deck unlevel.

If you skip checking the tire pressures and later find out this is your problem, you will have to reverse any adjustments you made prior to identifying you have a low tire. Skipping this step can create a lot of additional work for you.

Add air to your tires to bring your tire pressure up to the level shown on your tire side wall. The pressures for each of your drive tires should be equal.

Worn or Dull Zero Turn Mower Blade

A blade can become extremely dull and no longer cut the grass. It can find strips of uncut grass in your yard. A blade that has a worn sail will not be able to create sufficient airflow under the deck.

Airflow is needed to create a suction under the deck to lift the grass for a nice even cut.

Check your zero-turn blades for wearing on the sail. The sail is the high side of the blade. It should be the same thickness as the center of the blade. When the sail is thinner than the center of the blade it is time to replace your mower blade.

Check the sharpness of your mower blades. If they are dull, but in fairly good condition without large gouges in the cutting edge, go ahead and sharpen the blades.

When you find you have gouges in the blade edges or the edges are getting pretty thin from prior sharpening, replace your mower blades.

You can find instructions on changing and sharpening your zero-turn blades here.

Bent Zero Turn Mower Blade

Your blade can become bent from an impact with a solid object like a stump or rock. You may remember the exact time of impact because of a jolt or grinding noise from the blade impact.

Other times, the impact may not be great enough to make you aware of a potential problem that can cause a bent blade.

Either way, when you experience a bad and uneven cut, it’s a good idea to make sure your blades are not bent. There are a couple of different ways to check for a bent blade:

Check for a bent mower blade with it installed on your zero turn

With your mower parked on a flat-level surface, measure from the ground to the end of the blade. Record your measurement. Proceed with rotating the blade 180 degrees. Measure from the same point on the ground up to the blade end. Record the measurement.

If you have greater than a 1/8” difference in the two measurements, your blade is bent and must be replaced.

Before you remove your mower blade, check for damage to the spindle or spindle housing bearing to determine whether you need to remove the spindle housing to repair it. Follow the instructions below under the “Bad Spindle Bearing or Spindle” section of this article.

Check for a bent mower blade with it removed from your zero turn

Remove the mower blade and lay the old blade on top of the new mower blade. Check for any gaps between the two blades that can indicate your old blade has been tweaked or bent. Replace a bent mower blade.

Never attempt to straighten a zero-turn mower blade to reuse it. Doing so will compromise the metal and make it weak. It will be more susceptible to cracking.

A cracked blade spinning under your mower deck at high rates of speed is a recipe for disaster. Don’t put people, pets, or objects in the area at risk of injury or damage just so you can save a little money.

Unbalanced Zero Turn Mower Blade

A blade that is not balanced can give you an uneven cut. An unbalanced blade is one where the weight on one side of the blade is more than the other side. A zero-turn blade can become unbalanced when the dirt that is sucked into the mower deck wears more on one side of the blade.

It can also become unbalanced during the blade sharpening process. When more metal is shaved from one side while sharpening your blade, the blade will become unbalanced and heavier on one side.

There are a couple of methods you can use to ensure your blade is balanced:

Blade balancer: Use a tool called a blade balancer. This is a relatively inexpensive tool used to check your blade balance. Running an unbalanced blade on your mower can cause spindle housing damage and send a vibration through your zero-turn.

Nail on the wall: Place a nail in the wall with the head of the nail sitting about 3/4”-1” away from the wall. Place the center of the blade on the nail. Shave a little metal from the side of the blade that hangs lower until the blade sits level on the nail.

Bad Spindle Bearing or Spindle on Your Zero Turn Mower

A bad spindle bearing or spindle on your lawn mower can cause your blade to wobble which turns into a significant vibration when the blade spins at high speeds.

Check for a bad spindle or bearing in the spindle housing by grabbing each end of your mower blade. Rock it up and down to check for movement or a knocking sound. If you experience either of these symptoms, disassemble your spindle housing and check it for damage.

Replace a bad bearing or spindle. Some zero-turn manufacturers use spindle housings with sealed bearings. In this case, you will not be able to replace the bearing, you will have to purchase and replace the spindle housing assembly.

Bad Zero Turn Deck Belt or Pulley Bearing

The deck belt runs around your pulleys and spins your mower blades. When your belt is worn, it can slip and not turn your blades at the high speeds required for a good and even cut.

Replace a deck belt that has a glazed shiny appearance or one that sits deep in the pulley grooves. Additional signs your deck belt is worn and must be replaced is a stretched, cracked, or shredded belt.

In addition to checking the belt to make sure it is in good condition to turn the pulleys, you must inspect the pulleys. A bearing can fail in a pulley.

This causes your pulley to not sit flat and parallel to the deck. It may also restrict the movement of your pulley so it doesn’t turn smoothly.

Check the condition of each pulley by slowly turning each pulley by hand. Feel for a restriction and listen for a noise coming from your bearing.

Also, check to make sure the pulley is sitting securely on the deck and isn’t wobbly. If you find any of these symptoms when checking the pulley, the pulley must be replaced.

Zero Turn Mower Deck is Plugged

It is normal to collect grass clippings, mud, and other debris under your zero-turn mower deck. When the amount of debris becomes significant, it can interfere with airflow and the suction created under the deck to lift and cut your grass for a nice even cut.

It is important to routinely scrape your mower deck to keep it free of debris. Not only will it give you a nicer-looking cut, but it can also avoid overworking and overheating your engine.

The engine must work harder when it is required to turn blades into a buildup of grass with each turn of the blade.

While collecting grass under your deck can’t be totally avoided, it can be minimized with the use of a deck spray. This isn’t a miracle spray. It will not stop all grass from collecting under the deck, but it should reduce how often you need to scrape your deck.

It also helps to avoid mowing in wet conditions. Wet grass clumps and plugs your deck more quickly than dry grass clippings. Mowing in wet conditions also leaves more pronounced tire tracks in the yard giving the appearance of a bad cut.

Zero Turn Deck is Not Level

A deck that isn’t level, with the same deck height on the right side and left side, can cause your zero-turn mower to cut unevenly. Measure each side of your mower deck while parked on a level surface. Take measurements from the ground to the blade on each side.

Refer to your owner’s manual for the deck adjustment procedure for your zero-turn model as they vary by manufacturer and model.

In addition to checking the side-to-side measurements to ensure they are level, it is important to check the front-to-rear measurements. This is also known as the rake.

For most lawn mower decks installed a zero turn must be adjusted so the front of the deck sits slightly lower than the rear of the deck. Verify the measurements listed in your owner’s manual and follow the manufacturer’s instructions for making the necessary adjustments.

Engine Speed is Tool Low on Your Zero Turn

A fast blade tip speed is essential to achieving a good cut with your zero-turn. You must ensure you are running the mower at full throttle when your mower deck is engaged so your blades rotate at their fastest speeds.

If your engine no longer is giving you the power it once did, have a small engine mechanic run tests on your engine to determine the cause for a loss of power.

Zero Turn Mower Ground Speed is Too Fast

Running your zero-turn across your lawn too fast will not give the mower a chance to properly stand up your grass and cut it nicely. It could cause your mower just to push over some grass giving your lawn an uneven cut.

Adjust your mowing speed to your conditions. Thick, tall, heavy, or wet grass requires a slower speed than a standard lawn or dry grass. You will also need to slow down when mowing inclines as this puts extra strain on your engine.

Incorrect Overlapping of Path with Your Zero Turn

It is important to overlap your mowing paths to not leave extra strips of grass between paths. When I was getting used to my mower and trying to cut as much time off my weekly mowing task, I tried to space out my paths as wide as possible.

While I did save some time, I also noticed quite a few strips of uncut grass.

Zero Turn Mower Deck Shell is Damaged

A damaged deck shell can cause you to get an uneven or bad cut from your zero-turn mower. You may have accidentally hit a tree or a post that damaged your deck shell and compromised your cut.

You can try to fix your deck shell. If you are unable to do this you will have to replace the deck shell.

When pricing out a deck shell and having your lawn mower dealership swap the hardware for your new deck shell, it is a good idea to price out a full replacement deck. You may be surprised at the cost of labor to swap all the components over to the new deck.

Depending on the life left on your mower, you may want to spend a little extra and purchase the replacement deck.

Lawn is Uneven

If you have high spots in your yard from critters burrowing underground cause your mower to scalp the yard over the high spots. You’ll have to figure out a way to deter the critters from making your yard their playground. Roll your yard to remove any high spots.

You may notice scalping in unleveled parts of the lawn where there is an incline or a ditch. If you have a wide format mower deck, your deck is not able to flex and float over these areas often causing an odd cutting line into the side of a hill or shallow ditch.

A smaller format mower like ta push mower is best for these areas.