How do I look after a lawnmower?

A blunt mower blade tears grass rather than cutting it, leaving a ragged whitish finish that's more prone to disease. Sharpening is the single maintenance job that visibly changes the result, and cleaning the deck is what prevents most of the other problems.

Safety

What you'll need

• Spanner for the blade bolt
• Heavy gloves and eye protection
• File or bench grinder
• Scraper and brush
• Fresh engine oil (optional)
• Fuel stabiliser (optional)

Step by step

1. Disconnect the spark plug lead, or unplug and remove the battery.Every time, before touching anything near the blade. This is the step that prevents serious injuries.
2. Clean the underside of the deck after each use.Compacted grass restricts airflow, which is what lifts the grass for a clean cut, and it holds moisture against the metal.
3. Check the blade for damage as well as bluntness.Cracks, deep nicks or a bent blade mean replacement, not sharpening. A damaged blade at speed is dangerous.
4. Remove the blade, noting which way round it fits.Photograph it first. Fitting a blade upside down is a common error and it won't cut.
5. Sharpen along the existing bevel with a file, keeping the angle consistent.It doesn't need to be razor sharp — a clean, even edge is what matters. Take equal amounts off each end.
6. Check the blade balances before refitting.Rest it on a nail through the centre hole. If one end drops, take a little more off that side. An unbalanced blade vibrates and damages the bearings.
7. For a petrol mower, change the oil annually and check the air filter.A clogged air filter is a common cause of poor running and hard starting.
8. Over winter, drain the fuel or add a stabiliser.Modern petrol degrades within months and gums up carburettors, which is the most common reason a mower won't start in spring.
9. Store somewhere dry, and charge lithium batteries to around half capacity for long storage.Fully charged or fully flat storage degrades lithium batteries faster.

Tips

• Sharpen twice a season if you have a large lawn, once if it's small. The difference in cut quality is immediately visible.
• Buy a spare blade and swap them over — you can sharpen the spare at leisure rather than mid-job.
• Mow when the grass is dry. Wet grass clogs the deck, cuts badly and clumps on the lawn.
• A mower that won't start in spring is usually stale fuel. Draining it in autumn prevents the annual ritual.

Common mistakes

• Working on a mower without disconnecting the power — Mower blades cause severe injuries and engines can turn over unexpectedly. There is no exception to this.
• Not balancing the blade after sharpening — An unbalanced blade vibrates at speed and wears out the crankshaft bearings.
• Leaving petrol in over winter — It degrades and gums up the carburettor, which is the most common spring starting problem.
• Tipping a petrol mower the wrong way — Oil and fuel run into the air filter and cylinder. Check the manual for the correct direction.

Questions people ask