Why is My Lawnmower Not Cutting? Causes and Fixes

You are ready to continue your usual mowing schedule, which makes your lawn always appear lush and appealing. However, you notice that the mower is not cutting grass or making uneven cuts that ruin your garden. What could be the cause, and what’s the solution? 

Various issues can make a lawnmower not cut grass or make uneven cuts. These include a clogged deck, unbalanced wheels, bent or blunt blades, and a slow engine speed. Fortunately, you can examine your mower to pinpoint the exact problem and fix it yourself. 

If you are searching for ways to fix your lawnmower that isn’t cutting properly, you are in the right place. 

If You Aren’t Sure Where To Start, Consider Getting a Repair Manual

If you really aren’t sure what the problem is but want to fix it yourself, you can try reading a repair manual for your mower. Repair manuals are often released by the manufacturer itself to guide repair professionals in troubleshooting and fixing their equipment. As you can imagine, they are pretty helpful when you aren’t sure what the problem is or how to perform a specific task. 

Also, they are more detailed than the info I can provide here because they are model specific. 

So if you want to fix your equipment yourself, getting one of these can be a good option especially if you intend to use your tool for a long time as these guides can help you troubleshoot the most common malfunctions, not just the one you are dealing with right now. 

A good site to look for these is emanualonline.com – they have over 2,5 million repair manuals available, so there is a good chance they have one for yours too. Just make sure you get the one for your specific model!

With that said, here are some tips that should help with most mowers out there:

Uneven Tire Pressure 

As simple as it seems, the tire pressure can affect the quality of your mower’s cuts. Therefore, you need to confirm that the air pressure is consistent in all tires to avoid making the lawnmower unbalanced. (Obviously, this only applies to riding lawnmowers that actually have air in their tires.)

If you are not certain of the proper tire pressure, you can confirm from the manual or on the side wall of the tires.

Besides pressure, you might have set your lawnmower wheels at different heights making the mower sit unevenly (some lawnmower models require individual height adjustments on each wheel). If this is the case, setting all of the wheels to the same height should fix the problem. 

How to Fix

If you are mowing, stop the mower and check if all wheels are on the same height adjustment, depending on your model. If one of the wheels is higher or below the rest, adjust it.

You can check the tire pressure using a tire gauge and then adjust it to meet the specified pressure for your model. If you were using the mower, you should first let the engine cool down before checking the tire pressure.  

Damaged Wheels 

If one or more wheels of your lawnmower are damaged, they will cause the mower to be unbalanced, and the blades may be unable to cut grass. A damaged wheel will also make it harder for your riding or walk-behind lawnmower to move. The cutting blade will also lean on one side, causing uneven cuts. 

How to Fix 

The best way to identify if your mower’s wheels are damaged is by moving the mower for a short distance to see if there are any wobbling wheels. If lawnmower wheels are damaged, the only viable solution is to remove and replace them.

Your Mower Deck is Clogged 

While mowing your lawn, the grass clippings and debris may clog under your mower’s deck. The clogged debris will reduce the airflow that enables the mower to lift grass for the blades to cut, which will result in uneven cuts. 

Your mower deck may also get clogged if you don’t clean the lawnmower after each use or if you mow wet grass. 

How to Fix 

Though you cannot avoid debris from clogging your mower’s deck, you can reduce it. The first prevention measure is to mow dry grass and avoid wet grass since it clumps more. You can also apply the Teflon Silicone spray to reduce grass clogging. 

If your deck is already clogged, use a putty knife or stick to unclog it, then clean it. You should avoid putting your hands into the deck as the blades may cut you. 

The Lawnmower Blades are Dull

For your lawnmower to cut precisely, the blades must be sharp. If you have used the blades for a long time without sharpening them, they will become dull. Dull lawnmower blades tear the grass rather than make clean cuts. These cuts leave your lawn looking uneven and unprofessional. 

How to Fix 

The ultimate solution to fixing dull blades is sharpening them. However, you need to take precautions when sharpening the blades. You should stop the engine and disconnect the spark plug (gas-powered lawnmowers) or power cord (electric models) to prevent the blades from spinning.  

Proceed to check your mower’s blades and sharpen them using a file. However, if they are too rusty or have dents, it is best to replace them. 

Bent or Incorrectly Installed Blades 

The lawnmower’s blade can bend if it hits a hard object such as a rock when mowing. Bent blades will spin at an angle that causes them not to cut the grass effectively. Another possible reason for your lawnmower not cutting grass is incorrectly installed blades. 

If you’ve bought replacement blades or connecting back blades after sharpening, you must do it correctly for them to be able to cut grass. Installing the blades upside down will make your lawnmower not cut properly. You should also tighten the blades since loose blades will also cut unevenly. 

The continuous vibrations may also cause the blades to loosen up. If the blades are loose, they usually produce a rattling sound. 

How to Fix 

Turn off the engine, disconnect the spark plug/power cord, then tilt the lawnmower so that you can access the blades. Next, confirm if the blade is loose, installed incorrectly, or bent. If it is loose, you’ll need to fasten the bolt(s) that is holding it in place. 

You can check if the blades are installed correctly using the labels on the mower blades. Most lawnmower models will label the upper and lower parts with terms like “Bottom” to show which part should face the ground. Generally, the blade’s sail should always face upwards. 

If you are having trouble determining which side of the blade is up, check out this article

If the blade is bent, you must replace it with a new one. You should not try to straighten it since the metal will become weak and may fly out when you turn on the mower, posing a severe threat. 

Engine Speed

The speed of the blades can affect how well a mower cuts. For your blades to deliver a clean cut, the blades must be rotating at high speed. However, if the mower engine malfunctions, it will slow down the blades leading to bad cuts. 

While the blades should be spinning at high speeds, your mower’s ground speed should not be high. You should slow down the mower, especially while cutting through tall or tough grass. If the ground speed is too high, the blades won’t have adequate time to make clean cuts. 

How to Fix 

Ensure that your riding lawnmower is moving at a slower speed to allow the blades to cut the grass. If you are using a push lawnmower, avoid pushing it too fast. 

When mowing, you should also set your mower at full throttle to ensure the blades are spinning fast enough. If your engine is not responsive, seek help from a professional mechanic who will diagnose and fix any engine problems. 

Deck Problems

Various deck problems can cause your lawnmower to cut the grass inefficiently. If you have used your mower for a long time, it might form holes due to corrosion, vibrations, or minor accidents. These holes interfere with the air suction that enables the mower to pick grass, affecting the cut quality. 

The deck shell of your riding lawnmower may also get damaged if you hit a hard object such as walls or fences. Additionally, the accident may cause the mower deck to sit unbalanced, which will make the blade cut unevenly. 

How to Fix 

If you are familiar with repairs, you can fix the holes or the deck shell. However, the best decision would be to hire an expert to make all the necessary repairs to your deck. You can also buy another lawnmower if the repair costs are too high. 

Bent Crankshaft 

Like your blades, your mower’s crankshaft can bend, making the lawnmower cut badly. You can check if the crankshaft is bent by tilting the mower (make sure that the engine is off) to access the blades. Next, wear thick hand gloves and push the blades to see how it spins. 

If the center bolt that attaches the blades to the mower keeps wobbling as the blades rotate, it indicates that the crankshaft is bent. 

How to Fix 

You can straighten the bent crankshaft yourself (if you know what you are doing) or take it to a repair shop for straightening. 

If the repair would cost too much, you can always buy a new mower. Whatever you do, I do not recommend using the mower in this condition because a damaged crankshaft can eventually throw the blade off, potentially leading to serious injury. 

Why is My Lawnmower Blade Spinning but not Cutting?

Your lawnmower’s blade may be spinning but not cutting if it is loose or the pulley system is not working correctly. If you examine the lawnmower and find that the bolt that connects the blade to the mower is loose, you need to tighten it to fix the problem. 

Some lawnmower models have their blades connected indirectly to the engine through a deck belt and pulley system. If you have such a model, the following reasons could make the blade spin but not cut: 

  • The belt may loosen or fall off
  • Pulleys malfunctions 
  • Incorrectly installed blades 
  • A bad or loose spring 

The following are the different ways to troubleshoot your lawnmower and get the blade to spin and cut. 

Replace the Belt 

If your mower’s belt is damaged, you must replace it to get the mower back into action. However, this could be tedious, especially if you own a large mower. The first step is to remove the worn-out belt by adjusting the tension to loosen the belt. 

If your model does not have a tension adjuster, you can wear gloves and then lift them off the pulleys. Alternatively, you can remove the mower’s spring to reduce tension and take out the belt. 

Once you get rid of the old belt, place the new belt on the pulley system, then tighten it into place by adjusting the tension. You can check your mower’s manual to ascertain that you’ve installed the belt correctly. 

Replace the Spring 

To get to the spring, you’ll need to remove the belt. Once the belt is out of place, you can easily access the tension spring and replace it with a new one. 

Fix the Pulley 

If your pulley is loose or damaged, or the bearings are damaged, you can fix or replace them. You can use a ratchet and sockets to unscrew the pulley after removing the belt and then replace or repair it. Once done, put the belt back. 

Adjust the Tension

If your lawnmower model has the option of adjusting the tension of the belt, you can easily do so using a wrench or screwdriver. Adjusting the tension will increase the pressure necessary for the belt to function excellently. 

To adjust, place the belt on the pulley, then use a wrench or screwdriver to tighten them. However, take care not to over-tighten as it may tear the belt. 

Peter Toth

Hi! I'm Peter, the owner of BackyardGadget. Working around the house has always been a big part of my life. I've created this site to share my experience, and to help people choose the right tools for the job. Thank you for stopping by!

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