Maintaining your lawnmower: sharpening the blades and upkeep

A lawnmower with dull blades doesn't cut the grass, it tears it: the grass yellows at the tips and the lawn becomes more sensitive to disease. Conversely, a sharp blade, a clean deck and a well-maintained engine give a clean cut and extend the life of the machine. Mower maintenance takes a few hours a year, is done with simple tools and avoids expensive repairs.

When to maintain the blades

• Sharpen the blades at least twice a season, ideally every 20 to 25 hours of use
• If the cutting edge shows nicks or dents, the blade must be sharpened before the next mow
• Replace the blade as soon as it is too worn, deformed or cracked (a warped blade makes the machine vibrate hard)
• A cut that leaves white or shredded strands is the sign of a dull blade
• After hitting a stone or a root, check the condition of the blade immediately

The materials needed

To sharpen, you will need an impact wrench or a 19 to 24 mm wrench depending on the brand, a possible replacement blade, a sharpening stone, a flat file or an angle grinder, and protective gloves. Also plan a cloth, penetrating oil and a wooden block to lock the blade during removal.

Removing and sharpening the blade

1. Disconnect the spark plug or disconnect the battery before any work to avoid accidental starting
2. Tip the mower on its side (exhaust side up) and wedge the blade with a block of wood
3. Unscrew the center bolt with the appropriate wrench counterclockwise
4. Remove the blade and clean it: remove dried grass and gum with a scraper or penetrating oil
5. Sharpen the cutting edge with a flat file or a stone, keeping the original angle (about 30 degrees)
6. Balance the blade on a screwdriver passed through the center hole: it must not tilt to either side, otherwise remove a little metal from the heavier side
7. Refit the blade respecting the cutting direction indicated by the arrows, then retighten the bolt firmly

Cleaning and maintaining the engine

• Clean the deck and the underside of the mower after each mow: damp grass sticks and rusts the metal
• Check the oil level (4-stroke engine) and change it once a season or every 50 hours
• Clean or replace the air filter if it is blocked by dust and grass
• Check the spark plug: a fouled plug or one with the wrong gap prevents starting
• For battery models, clean the contacts and recharge the battery at room temperature

Preparing the mower for winter

1. Empty the fuel tank completely or use a stabilizer additive to avoid gum deposits
2. Run the machine until it stalls to empty the carburetor
3. Change the oil before storage (used oil stagnates badly in winter)
4. Clean the deck, grease the wheels and axles with a light oil
5. Store the mower under cover, raised if possible, with the blade sharpened to start in spring

The mower no longer starts: quick checks

If your mower refuses to start, check in order: the fuel level (fuel older than six weeks degrades), the dirty air filter, then the blackened spark plug or one with the wrong gap (0.7 mm in general). Finally check the safety cut-off switch and the starter handle: a slack cable prevents the engine from turning over. Most starting problems are solved with these four points, without going through the workshop.

For sharpening, know that a new blade installs easily: a compatible blade costs 15 to 30 € and mounts exactly like the old one. If you mow sandy or very stony ground, plan a replacement every season.

The mistakes to avoid

• Sharpening a blade that is too worn: beyond a loss of 2 to 3 mm, sharpening weakens the blade, better to replace it
• Mowing wet grass with a dull blade: the grass tears and blocks the deck
• Running the mower on its side without disconnecting: it is the leading cause of accidents
• Letting dried grass accumulate under the deck: it rusts and unbalances the blade

With a sharpened and balanced blade, a clean deck and a checked engine, your mower will cut cleanly, start on the first pull and accompany you for many seasons. This maintenance ritual of a few hours a year is well worth the price of a new machine or a repair at the garden center.