How To Change a Lawn Mower Blade

Lawn mower blades wear out eventually and will require changing to keep those missed grass patches in your yard at bay.

A mower with clean, sharp blades will allow you to mow less frequently and maintain a healthier lawn.  Of course, if you have own a reel mower, you won’t have to change the blades at all, they just to be sharpened occasionally. 

Follow these time-saving steps to change your blades:

  1. Buy replacement blades. The new blades available in hardware and home improvement stores are usually sharpened, pre-weighed, and come with replacement nuts. They’re either universal or specific fit, so make sure that you’re purchasing blades of the same length as the previous ones. Come prepared with the make and model number of your mower. You can take a pic or bring in the owner’s manual as well.
  2. Let the gas run out in the mower or drain out any remaining gas using a siphon hose (you can buy a hand siphon pump in any auto parts store or hardware). This will prevent any gas from spilling onto you, the lawnmower, or the grass when you turn it.
  3. Tilt your mower back toward its handle and support it with a weight. All mowers are different, though, so it’s a good idea to look at your owner manual to make sure you’re doing it right.
  4. Unplug your spark plug. You shouldn’t have any problem with shorting out or an electrical flare-up since you’ve already drained out the gas, but it’s always better to err on the side of safety!
  5. Get a socket wrench to unbolt the mounting bolt for the blade with one hand, and with the other hand make sure that the blade doesn’t turn (this process can also be done with a partner). Make sure not to lose any mounting hardware or washers in the process, since they are reusable.
  6. As you’re removing the blade make sure to notice what position the blade is in while you’re removing it. The new blade should be mounted the same way, typically with the blade’s sharper edge counter-clockwise with the hose assembly. All lawn mowers are different, though, so it’s especially important to pay close attention to how the blade to be changed is installed and copy that position when installing the new blade (If the blades still appear to be in good condition you can salvage them and have them sharpened. However, replacement blades are pretty inexpensive, and most people choose to buy a new set).
  7. Put on some heavy duty gloves for safety. You can use a piece of wood placed between the mower deck and the blade to make sure nothing’s turning while you’re doing the installation. Reinstall nuts and washers as you line up the new blades. Check the owner’s manual for torque specs on tightening the nut. No owner’s manual? Make certain that you don’t over-tighten the nut since that can warp the blade. Be careful tightening the bolts since they’re probably a lot sharper than the previous ones.
  8. Mount the new blade so that it has absolutely no wobble whenever it’s moved up or down. Remove any wood pieces or props that have been used to keep the mower from moving. Don’t start up the mower for approximately 30 minutes to one hour to make sure that any oil has returned to the motor.
  9. Time to refill the lawn mower’s gas tank and do a pre-mow checkup. Double check the air filter if necessary and reattach your spark plug wire. You should be all ready to go!

Changing the blades on older mowers can be quite difficult and if you cross thread the bolts, it may be time for an upgrade.