This Fix-It Guide on rotary lawn mower repair tells how a rotary lawn mower works, what often goes wrong, how to identify a rotary lawn mower problem, and what parts and tools you will need to fix it. It then gives step-by-step instructions for how to service the mower blade, how to service control cables, and how to replace the wheel drive belt. This Fix-It Guide also refers to rotary lawn mower repair, small engine repair, electrical cord repair, motor repair, and switch repair for more help fixing a rotary lawn mower.
How Does a Rotary Lawn Mower Work?
Components of a typical rotary lawn mower.
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 re-cut 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 with a Rotary Lawn Mower?
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 a Rotary Lawn Mower Problem?
- If a rotary lawn 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 a rotary lawn 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 a rotary lawn mower engine won’t start or runs poorly, see the Small Engine Fix-It Guide.
- If a rotary lawn mower 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 Do I Need for Rotary Lawn Mower Repair?
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
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!
What Are the Steps to Rotary Lawn Mower Repair?
Service a rotary lawn 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 re-installation.
- 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 rotary lawn mower 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 a rotary lawn mower 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.
