Time to cut the lawn--again?! A rotary lawn mower makes the job easier, but it doesn't cut the grass without your help, so you'd better get started. Hopefully, it will start up quickly and be back resting in the shed soon. If it's reluctant to work or just plain stubborn, here's what you can do.
How Does It Work?
Components of a typical rotary lawn mower.
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A rotary lawn mower is a powered machine for cutting grass. Rotary mowers come in self-propelled or push types, powered by either a gasoline engine or an electric motor. It's called a rotary motor because a long thin blade is rotated from its center to cut grass evenly. Some rotary mowers have a mulching blade designed to lift grass clippings, then cut and recut them into finer pieces that serve as mulch for the lawn. See the Riding Lawn Mower Fix-It Guide for information on larger rotary motors.
What Can Go Wrong?
The mower may cut unevenly or tear grass rather than cut it. The mower may vibrate excessively or be noisy. The engine may not start, or may run poorly. The engine may run, but the mower won't move. The electric motor may not run.
How Can I Identify the Problem?
If the mower cuts unevenly, first check and clean a dirty blade. If this fails, service or replace a dull, unbalanced, or bent blade (see below), and check the owner's manual to correctly adjust the wheel height.
If the mower vibrates excessively, you can balance or replace a blade (see below). Also, with the mower not running, clean clippings from under the mower deck and clear the discharge chute following the owner's manual instructions. Never work under the mower deck with the mower running!
If the engine won't start or runs poorly, see the Small Engine Fix-It Guide .
If the engine runs, but the mower of a self-propelled machine doesn't move, check the drive system (see below).
If an electric mower won't start, test the electrical cord, motor, and switches.
Fix-It Tip
One of the Fix-It Club's mantras is: "Save the owner's manual!" You'll discover why as you try to disassemble and fix a rotary lawn mower or practically any other household device you have.
What Parts, Materials, and Tools Do I Need?
You can find many replacement parts through local hardware stores and other aftermarket suppliers. Also check with the manufacturer. The tools you will need to fix a rotary lawn mower may include these:
- Screwdrivers
- Scrap lumber
- Work gloves
- Hammer
- Wrenches
- Multimeter
- Flat file
What Are the Steps to Fixing It?
Caution!
Why do you need to disconnect the spark plug cable before beginning any repairs? Rotating the blade by hand can make the engine start--if there is spark. Think of those old movies where the pilot would start a plane by turning a switch ("Switch on!") and the helper would spin the propeller. Now imagine that the helper had his arm around the prop!
Service the mower blade:
- Disconnect the spark plug cable for safety.
- Use scrap lumber to wedge the blade into a stationary position so it won't turn when you loosen it.
- As needed, remove the blade with wrenches and a gloved hand (for protection). Use a pencil to mark the side of the blade that faces down for proper reinstallation.
- Inspect the rotary blade for damage and replace as needed. Some blades have a metal bar called a stiffener that also should be checked. If necessary, replace the blade with one as recommended by the manufacturer.
- Use a flat file to sharpen the blade, filing only in one direction. Follow the original contour of the blade edge.
- Insert a screwdriver through the center hole and hold the screwdriver to determine if the blade is balanced. If it is not, use a file to trim metal from the heavier (lower) end until it is evenly balanced.
- Reinstall the blade, making sure that the blade is installed as it was removed for proper operation.
- Reconnect the spark plug.
Service control cables:
- Disconnect the spark plug cable for safety.
- Remove the controller cover and loosen the locknuts.
- Remove all slack from the cable, reposition the locknuts as needed, and tighten the locknuts.
- Test the controller by moving it through the various positions and making sure it responds appropriately. If it doesn't, readjust it.
- Reconnect the spark plug.
Fix-It Tip
Some rotary lawn mowers require that you remove the entire deck cover to access the drive belt. To remove the deck cover, unscrew the bolts and slide the cover off. The owner's manual probably will include more instructions.
Replace the wheel drive belt:
- Disconnect the spark plug cable for safety.
- Remove the cover over the wheel drive belt.
- Tilt the pulley toward the engine and remove the belt from the pulley.
- Tilt the mower to remove the other end of the belt from around the blade pulley.
- Install the new belt in the opposite order: around the blade pulley then around the wheel pulley.
- Tighten the wheel pulley adjustment so the belt moves 1/4 inch when pushed halfway between the two pulleys. Readjust as needed.
- Reconnect the spark plug.