How to Adjust Blades on a Walk Behind Mower

Safety Measures

• Any time you must work on your mower by turning it on its side, you must ensure the engine won’t turn over while you’re working. Turn the mower off, remove the key and disconnect the spark plug wire. Use a siphon pump to remove gas and oil from the mower before you begin working, as otherwise it may spill out onto your work surface. If you prefer, run the mower out of gas and then just remove the oil.

Adjusting Mower Height

• Most walk-behind mowers will allow you to adjust the height with the mower sitting on the ground, so you won’t need to remove the spark plug or drain the gasoline. However, you always should make sure the engine is off before working. Set the mower on a level surface, and measure the distance between the surface and the blades. Then adjust the height, usually using a lever or raising or lowering the wheels.

Sharpening Blades

• If blades are dull, you either can buy new ones, or sharpen them with a file or grinding wheel. Whether replacing blades with new ones or putting sharpened blades back in, make sure the cutting edge is facing the right way. Many blades are marked “bottom,” so face that side toward the ground, or else look for the serial number, which also should face the ground. Use your mower manual as a guide for how tightly you should attach the blade, as you’ll want to maintain the proper torque.

Professional Help

• In some cases, you shouldn’t try to adjust blades on a mower yourself. Although sharpening or replacements are simple enough, adjusting the balance on a lawn mower usually is more difficult, so if you don’t know how to do it, seek professional help. Likewise, any time the mower strikes an object and begins to shake or vibrate, you should check the blades. If they seem fine but the mower still is unstable, take it to a professional to check it out: it may need aligning or a replacement crankshaft.