Change a lawn mower blade safely and easily

I needed to change a lawn mower blade this weekend, which meant I had to remove the stubborn old blade first. That proved to be a challenge, but not an insurmountable one. I learned the secret of changing a blade without hurting myself, and without a torque wrench, even when the stubborn bolt doesn’t want to turn.

To remove and replace a lawn mower blade safely and easily, you need a length of 2×4 board long enough to stand on, a small plastic pan, the biggest socket wrench you can find, and a socket that matches the bolt on your mower. If you don’t have a socket wrench, you can use a regular crescent wrench, but you want the biggest one you can find. Longer wrenches give more leverage, and you need lots of leverage to free a stuck bolt.

First, and most importantly, pull the wire on the spark plug. This will keep the engine from starting accidentally while you’re working on it. I know how rarely one of these engines to starts on the first pull when we want them to, so it’s hard to imagine them starting accidentally, but err on the side of safety.

Next, tilt the mower over. Position your plastic pan underneath the gas cap to catch any gas that might drip.

Remove the old lawn mower blade

Hold the blade still with a board while you change a lawn mower blade
Position a board so the blade doesn’t move if you turn the bold counterclockwise. Stand on the board while you turn the bolt.

Lawn mower blade removal direction is another common question. It’s the same as any other bolt–righty tighty, lefty loosy. The problem is, the bolt tends to be really tight, and on something that isn’t stationary. So we’ll fix those two problems.

Position the 2×4 so that the blade can’t turn if you turn the bolt counterclockwise. Stand on it with at least one foot.

Set the socket wrench to turn counterclockwise with force. Now put the socket wrench on the bolt, and while still standing on the 2×4, lean into it until it turns. The bigger the wrench and the further toward the end that you hold it, the more leverage you’ll have. I’m pretty sure King Kong runs around tightening these bolts while nobody is looking, so be ready to exert some force. Just exert that force carefully, so your hand doesn’t slip off and hit something sharp.

If the bolt really, truly won’t budge, you can try tapping on the end of the wrench with a hammer while standing on the 2×4. That doesn’t seem like it would be good for the wrench, but if I were desperate, I could see myself doing it. I’d rather damage a socket wrench than my hands.

I’ve heard of people claiming it takes half an hour to remove a blade. Using this method, it doesn’t take that long. I had mine off in about five minutes.

Install the new lawn mower blade

To put the new blade on, reverse the direction of the wrench and move the 2×4 to the other side of the blade. Then tighten the bolt by turning it clockwise. You don’t necessarily want to crank it down with every ounce of your might. But you do want to secure it tightly. A lawnmower blade is something you don’t want flying off. Then again, every time you hit a stick or something else you didn’t mean to hit, the bolt tightens a little.

As tempting as it can be to pay someone $25 to swap the blade, it’s not necessary. If I can do it using this technique, pretty much anyone else can too. I’m not an imposing physical presence. The lawnmower is not intimidated by my 5’9″, buck-fifty frame.

A note about sharpening blades

One other thing. If you sharpen your own blades, sharpen them to the sharpness of a butter knife, not a samurai sword. New blades are only about as sharp as a butter knife. If you sharpen them sharper than that, they don’t last as long. And you’re more likely to injure yourself while handling one.

And when you’re done, remember to reattach the spark plug wire. You don’t need the frustration of not being able to start the mower after you’re done.

Further reading

And if you have trouble starting your mower on a regular basis, I know a slick trick with Marvel Mystery Oil and synthetic oil, and some advice on how to winterize your mower at the end of the season.

If you happen to have one or more height adjusters that are stuck so you can’t raise or lower the mower deck, here’s how to fix that.

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