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How to change the blade on a walk-behind lawn mower

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You should check your cutting blade at least once a season, or any time you strike an object. If you strike an object and your mower seems to vibrate excessively, you must have it checked out by a servicing dealer for a bent crankshaft or other damage. If the tips of your grass are turning brown between mowing, it is a sign that your blade may be dull. Damaged grass needs more watering and is more susceptible to disease. A blade should be replaced if it's chipped or bent or too worn to be sharpened.

Step 1

Because you'll need to turn the mower on its side to change the blade, there's the potential for spilled oil and fuel. To avoid this, run the mower until it's out of gas. The most efficient way to drain the fuel tank using the Arnold Siphon Pump, which can be purchased on this website or where mower parts are sold. To avoid burns, use caution when working around a hot engine. If time allows, let the engine cool down before you change the blade. First, remove the spark plug wire to assure the mower won't accidentally start.

Step 2

Tip the mower on its side with the engine air filter facing up. This will keep engine oil from getting into the carburetor and air filter. Inspect the blade for wear or damage. You should check your cutting blade at least once a season to make sure it's sharp. A dull blade will tear rather than cut the grass, and can turn grass tips brown, making your lawn not look its best. Also be sure to check the blade for damage any time you strike an object. If you hit something and your mower vibrates excessively afterward, have a servicing dealer check it for a bent crankshaft or other damage.

Step 3

If you decide to replace the old blade, you may want to wear gloves to protect your hands from any sharp edges. Use the Arnold Blade Removal Tool to hold the blade in place. The Arnold blade removal tool can be purchased on this website and where mower parts are sold.

Step 4

Using the proper size socket, loosen the bolt securing the cutting blade to the engine drive shaft. Some units may have two additional bolts securing the blade adaptor to the blade. Loosening them before you remove the blade from the unit will make your job easier. Before the blade is removed, make note of the orientation of the blade. You'll want to assure that the replacement blade is oriented the same way, with the fins pointed up. Remove the blade from the mower and keep the blade adaptor parts for installation of the new blade.

Step 5

If you simply need to sharpen your blade, instead of replacing it, you can use the Arnold Blade Sharpener and Balancer, which can be purchased from this website, or where mower parts are sold.

Step 6

Assemble the new blade and blade adaptor on the engine crankshaft. Tighten the blade bolt to the proper torque setting as indicated in your operator's manual.

Step 7

Remove the blade removal tool and return the mower to the upright position. Reconnect the spark plug wire and you're good to go!

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