How to Replace a Lawn Mower Blade
This simple five-step project will keep your walk-behind mower—and your lawn—in peak condition
Replacing your lawn mower blade regularly will lead to better and cleaner cuts on your lawn.
The best cut for your yard comes from a sharp lawn mower blade. A dull blade damages your grass by creating a ragged cut, which can lead to bare patches and other eyesores, as well as invite disease. A dull blade also stresses the lawn mower’s motor, making it work harder. That means your mower will use up more battery power or gasoline per cut.
With summer mowing season coming up, it’s worth learning how to remove the lawn mower blade yourself and how to place a sharpened blade onto your mower.
- Replacing Blade: Disconnect From Power Remove Blade Sharpen Blade Reinstall Sharpened Blade Secure Blade
How to Replace a Lawn Mower Blade in 5 Steps
You can replace the lawn mower blade from your walk-behind mower in five steps. If your mower is a gas model, follow these guidelines after running the mower dry or siphoning out the gas (a turkey baster works as well) to prevent a fuel spill when the mower is tipped on its side.
1. Disconnect Your Lawn Mower From Power
Make sure there’s absolutely no way the engine can jump to life. With a battery mower, remove the batteries; with a gas mower, remove the spark plug. Then turn the mower on its side. In gas mowers, you’ll want the air filter facing up to prevent oil from saturating the filter.
2. Remove the Lawn Mower Blade
Safety is paramount here. Put on heavy work gloves so that the sharp blade doesn’t cut you. Secure the lawn mower blade by lodging a 2x4-inch block between it and the mower deck (a C-clamp can help hold it in place if needed). Then use a wrench or socket to loosen the fasteners that anchor the blade to the drive shaft. There may be one bolt or two, with or without special washers.
3. Sharpen the Lawn Mower Blade
Once you’ve removed the blade assembly, take a picture of it with your phone so that you know the right way to put all the parts back together. (Your owner’s manual should also have a drawing of this.) Then take the lawn mower blade into a shop for sharpening.
If you’re an advanced DIYer, you could try sharpening the blade yourself using a metal file or a bench grinder. John Galeotafiore, who managed lawn mower testing at Consumer Reports for years, says that if you already own a Dremel rotary tool, that brand’s Lawn Mower & Garden Tool Sharpener attachment (Amazon, Home Depot) can help in sharpening the blade.
4. Place the Sharpened Blade Onto the Lawn Mower
Put the blade assembly back together, following the picture you snapped earlier. It’s important that the blade’s cutting edge follow the lawn mower’s direction of rotation. The wings of the lawn mower blade will be oriented up toward the mower deck, and any writing on the blade will likely be facing away from the deck. If the blade bolt comes with a washer, its concave side will be facing the blade.
5. Fasten the Bolts to Secure the Blade
Once you’re ready to tighten the bolt, put the work gloves back on. Reinsert the wooden block—on the opposite side of the mower deck this time—and tighten the bolt using a combination wrench.
Some manufacturers recommend using a torque wrench for this task because overtightening a bolt could cause it to crack, while undertightening it could allow the lawn mower blade to fly off while the mower is running.
Before flipping the mower back upright, take a few minutes to clean out the underside of the deck and apply a light coating of silicone spray, if you have it. This will prevent the built-up clippings from compromising airflow. Along with a sharpened blade, that measure could make the mower more energy-efficient while keeping your lawn and your lawn mower in tip-top condition.
If your mower is beyond repair, check our full lawn mower ratings and recommendations.
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