How to Replace Lawn Mower Blades: Do’s and Don’ts

The quality of your lawn mower’s blades has a huge effect on not only how it cuts but also the health of your lawn. As you mow, you may hit a rock or branch that damages the blade so badly that you must change it. Mower blades also simply wear out over time. If your mower vibrates or struggles to cut grass that isn’t heavily overgrown, it might be time for a blade change. Here’s a quick look at how to replace lawn mower blades yourself and treat your lawn a little better in the process.

Gear Up

Changing a lawn mower blade isn’t that hard on most mowers. Before you begin, there are a number of items you’ll need to gather, including:

• A replacement lawn mower blade for your mower’s make and model
• Adjustable or socket wrench (to remove bolt holding the blade on)
• Shop towels
• Wire brush

If you want to clean things up while you working grab a scraper too.

Safety First

Over time, your mower’s blade will become chipped from hitting rocks, branches and other debris. When a blade is severely damaged, it will need to be replaced entirely. Start by removing the spark plug to prevent an accidental start-up. If you have a push mower you can turn the mower on its side. To prevent fuel from leaking out, be sure to turn it so the carburetor is on top. If you have a riding mower or lawn tractor take the extra steps to remove the mower deck. Most mower decks can be removed with simple hand tools and then slid out from underneath the mower. Once the mower deck is disconnected it can be turned over to access the blade.

Before you start to take the blade(s) off, always wrap the sharp ends of the blade in shop towels to protect yourself from injury. Even a dull mower blade can give you a nasty cut. Removing the blade is as simple as holding it steady and loosening the anchoring nut. We recommend using a block of wood wedged against mower deck and the blade to prevent the blade from turning.

Out With the Old

Grab a wire brush and clean up the head of the nut or bolt holding the blade as it is likely caked with dirt and grass clippings. If it has been an especially long time since your last mower blade change you may want to use a little penetrating lubricant to make things easier. Next use an adjustable or socket wrench to loosen the bolt in the center. For stubborn bolts an impact gun (either electric or pneumatic) can make quick work of the job. Before removing the blade, use a permanent marker to note which direction the sharpened side is facing. Once you have the bolt off, slide the blade and retaining bracket off the shaft. If your mower has more than one blade, replace them all at the same time to maintain consistent cutting performance.

Now is a great time to give your mower deck a good cleaning if you have time. A clean mower deck is more effective at ejecting grass clipping and less prone to bogging down.

Mount the New Blade

Compare the new blade with the old blade to make sure they match. The blade angle needs to match so the grass is lifted and blown away the correct direction. The new blade may be slightly longer if the old blade saw a lot of harsh use.

With the new blade wrapped in your shop towel, place the blade on the shaft, followed by the retaining bracket, and reinstall and tighten the bolt. Although most mower blades are designed so they can only be installed with the correct side facing down, make sure the sharp side of the blades is facing the same way as your old blade. If you have a push mower you can now put it back on its wheels, while riding mower/lawn tractor owners can reinstall the mower deck. Reconnected the spark plug. If you have a push mower that you stood on its side let is sit flat on the ground for 10 minutes to allow any oil to drain back into the bottom of  the engine, otherwise you may get a smoky surprise. Start the engine to make sure there’s no vibration and that the mower is cutting properly. Vibration will indicate an issue with your installation, such as a loose bolt or crooked blade.

Changing the blade on your lawn mower is a quick and easy process. Performing this maintenance yourself rewards you with the satisfaction of a job well done. With a couple shop towels and a wrench, you can get your damaged blade swapped out in no time.

Check out all the lawn & garden products available on NAPAOnline or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to replace lawn mower blades, chat with a knowledgeable expert at your local NAPA Auto Parts store.

Image courtesy of Flickr.