How to Replace a Lawn Mower Blade




Introduction: How to Replace a Lawn Mower Blade

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Lawn mower blades must be replaced after so many hours of cutting, and the steps in this instructable explain how to perform this simple parts replacement.

Broken, dull, damaged, and mismatched mower blades can cause a number of easily-noticed symptoms.

Damaged mower blades can cause excessive vibration in the mower, while dull mower blades usually get noticed by the ugly, irregular patterns they make in the lawn.

Mower blades can be sharpened several times to extend their life and ensure that your grass gets a healthy cut, but they can only be filed so many times before a blade replacement is necessary.

If you need to replace a lawn mower blade, you can do so at

Homeowners can save themselves quite a bit of money performing simple repairs like this one. New mower blades tend to be reasonably priced, and mower blade replacements usually only require the use of a wrench.

For information about matching a replacement mower blade to your mower, please read the article, Lawn Mower Blade Measurements and Types.

Steps to Replace a Lawn Mower Blade

Mower blade mounting designs vary, but the basic steps are usually the same. Most mowers have use a very simple blade mounting design like the mower we use below as an example .

Step 1: Set the Mower on Its Side

Always set the mower on the side that does not have a carburetor so that the mower's fuel does not leak out.

Make sure the gas and oil caps are screwed on tightly before tipping the mower.

Step 2: Remove the Fasteners Holding the Mower Blade On

This just means removing one nut on our example mower, and this is usually the case for most mower models.

Use one hand to steady the blade when first loosening the nut.

Step 3: Remove the Old Mower Blade

Mower Blade Mounting Location

Step 4: Install the New Blade

Most mower designs will not allow the mower blade to be installed with the wrong side down.

Our example mower blade and its retaining plate are shaped so that the blade can only be installed in the correct position

It is possible to incorrectly install mower blades on some mowers. And it's always possible to install a blade too loosely.

Vibration and poor lawn cutting will quickly make a poor mower blade installation noticeable. A quick adjustment is all it takes to get back to work in the event of an incorrect installation.

Step 5: Conclusion

The surprising thing about this repair might be how easy it is, especially since many lawn mower owners do not take the opportunity to save money on tool repairs by doing them at home.

If your mower blade is dull, damaged, or heavily worn, visit our Lawn Mower Blades page to start your search for a compatible match and get started with this fast and easy repair.



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    22 Discussions


    my apologies for shouting, but to avoid any of you being called "lefty" your attention was required

    See this video for a safer way!

    This is the worst Instructables. First not disconnecting the spark plug. Second not having gas tank emptied to prevent gasoline spill. Third block the blade from rotating!

    Doe it make any difference how the blade is installed compared to piston position? For ease of starting and engine balance.

    If you've never done this task before, this is NOT the Instructable to follow. You're much better off following drezac's instructions in his comments below. Otherwise, you're liable to get some bruises or cuts or worse.

    Besides not mentioning the horrific safety item of not removing the spark plug wire first to avoid an accidental starting of the lawnmower with your hands around the blade, just look at that photo with the bare hands holding the blade between one's fingertips. That's just asking for trouble. Also, note the hand on the ratchet wrench - nobody holds a ratchet wrench like that in a situation when a good amount of force must be applied.

    BTW, with the underside of a mower that dirty with crusted-on grass and gunk, you just know that that mower blade hasn't been serviced in a long while and is not going to come off with a few simple turns of the ratchet.

    Also, check out that last photo - NOW the guy is going to put on a protective glove. (Maybe the glove in this photo is necessary to hide the fingers lost in the execution of the previous Instructable steps....)

    Need mower blades?

    I replaced the mower blade, but the shaft rotates when I try to tighten or loosen the bolt. What is the problem?


    2 years ago

    Drain your gas first. You can siphon it to make it easiest. Don't worry about a little left in the tank. The bigger concern is tilting the mower with the MUFFLER in the air. Otherwise, you will likely drain oil into the muffler and it will smoke terribly until it all burns out. There isn't an easy way to clean oil out of a muffler, especially if the bolts/threads are rusted.

    Furthermore, use a breaker bar or a ratchet with a pipe if you don't have an impact gun handy. A wrench is much more likely to slip off and leave you with scrapes and cuts. You can use a C-clamp or anything else to stop the blade from rotating so you can use both hands to steady the tools.

    If you buy parts from your local mower shop, you'll be more likely to get the right part and have it that day. You can take in your old blade or just the model numbers from the frame if you don't know the part number.

    If you're looking to sharpen your blade, make sure to check the balance. You can buy a blade balancer or you can use a screwdriver with a round shaft passing through the center hole of the blade. If one side keeps dipping down, grind more off of that side until it balances.

    Step 1 should read: Remove plug wire from plug. The last thing anyone wants to see is a lost finger because you accidentaly started your mower.

    THANK YOU! Thank you for easy to understand instructions plus pictures. My boyfriend AND my adult son BOTH told me that I COULD/SHOULD NEVER set my lawn mower on it's side - EVER. I told them it was safe if I put it on the proper side - but they said there was NO "proper" side.
    They agreed to settle on whatever YOU said, therefore I WON and was able to change my blade without any more interruption!
    Thank You Again!

    I revise any statements i may have said over 2 years ago to: great do it yourself ible!

    my great uncle would not agree with you, neither would his two missing fingers, you can get the blade to spin around once with the same amount of force it has when it is running by simply building up compression in the chamber, that is why they tell you to take the spark plug out to remove the chance of compression, also, all you have to do is turn the fly wheel to create a spark, and what little fuel is in the chamber will ignite and give that extra umph to kick that blade around. Please for the sake of your fingers, always remove the spark plug

    Small world !!!! i just ordered some parts for a mower from you guys !!!!!!!!!!!!!!!!!!

    I use a pneumatic impact gun to remove mower blades. Bang and it is done. If I had to do it with hand tools the last tool I'd pick would be a ratchet. I'd use either a breaker bar or the combination wrench like what you're putting the blade back on with. A few taps with a mallet or scrap of wood on the end of the tool in the direction you want to spin would loosen the nut fast.

    I get dozens of sharpenings out of a blade too not just a few like you said. I sharpen my tractor blades every other cut and only replace them every other year.

    Make sure to hang on to any mower pieces that help mount the blade, like the retaining plate pictured in Step 3.

    1 reply

    That mower blade and nut look really clean compared to mine. How do you get the nut off when everything is covered with the green-black crud that won't come off?

    I agree with rimar2000, all you need to do is sharpen the blade on a grinder.

    you should disconnect the spark plug anyway even if it's one in 10000 it can happen.