Installing Lawn Mower Blades Upside Down Is A Big Mistake. Here's Why

While you'll have some lawn mower maintenance tasks that should be done after every mow, others can be scheduled or only done when badly needed. Such is the case of replacing lawn mower blades. When your machine doesn't yield its usual clean results, it's very likely due to a dull cutting edge. Signs that point to a blunt blade include unevenly cut grass, a noticeably harder-working mower, and possibly clumps of turf thrown around. All these can be addressed by sharpening your equipment or simply acknowledging the signs that it's time to replace your mower blade entirely. However, though this is easier to do, there's one big mistake inexperienced and first-time lawn mower owners often commit — installing the new blade upside down. 

The lawn mower blade's wings (the curved features at the ends) are designed to face up toward the mower deck, creating airflow to send the cut grass to the bag or out the side of the machine. The sharp, beveled edge should face down and lead into the grass when the blade spins. Having them face the other way around will cause the upside-down wings (which will be much closer to the ground than the blade would be) to hit the rocks and soil when mowing, leading to serious blade and mower deck damage. The dull edge, meanwhile, creates a messy lawn, resulting in yellow or brown grass and leaving it more open to disease.

Dull mower blades will damage your lawn in more ways than one, so it's crucial to check for signs that your blade needs sharpening if you want greener grass before you start mowing. In many cases, you might just opt to replace it. Installing a new blade may seem tricky, but you can overcome this by being prepared and knowing what it means to orient the blade correctly. For good measure, take a photo of your existing blade for reference after flipping your equipment. Before turning the machine on its side, be sure to remove the battery or unplug it if you are using an electric mower. If you have a gas model, disconnect the spark plugs and empty the gas tank. Consult your user manual, if it's available, to know how to safely remove and replace a blunt blade. New blades also often come with instructions or stickers saying "this side up" or "grass side." Follow them to install the blade correctly.

After removing the old blade, put it aside and position the new blade. The sharpened cutting edge should face toward the grass. The curved wings must face upward or toward the mower deck. When in doubt, refer to that photo of the old blade you took earlier. Align the blade correctly, and tighten the center bolt securely into place using a torque wrench. Check for wobbling before flipping your mower back and using it again to trim your lawn.