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Maintenance

Brush cutter maintenance

A few minutes of care keeps a brush cutter starting first-pull and lasting a decade. Here's the simple maintenance routine for petrol and cordless machines.

By · Updated · first published

In short:Brush cutter maintenance is mostly about fuel and cleanliness: use fresh fuel mixed at the manual's ratio (or alkylate fuel), clean the air filter regularly, check the spark plug each season, grease the gearbox at the cutting head as the manual specifies, and check the oil on four-strokes such as Honda GX and Makita MM4 engines. Keep blades sharp and line fresh, clean grass from the head and guard, and before winter run the fuel dry and store batteries part-charged.

Petrol: the essentials

  • Fuel is everything. Use fresh fuel mixed at the correct ratio, or ready-mixed alkylate fuel. Stale fuel is the number-one cause of starting problems.
  • Air filter. Clean it every few uses — a clogged filter chokes the engine. Replace it yearly.
  • Spark plug. Check and clean each season; replace it once a year. A fouled plug means weak or no starting.
  • Gearhead grease. Add a little grease to the angle gearhead periodically per your manual.

Cutting head and blade

  • Replace worn line before it gets too short to feed.
  • Keep metal blades sharp and swap them when the teeth round off — a blunt blade is slow and dangerous.
  • Clear grass build-up from around the head and guard after each use.

Winter storage

  1. Petrol: drain the fuel or run the carb dry (or use alkylate fuel that keeps for years).
  2. Clean the whole machine and wipe it down.
  3. Batteries: store part-charged (around 40–60%) in a cool, dry place — never fully flat or in the cold.
Golden rule: most "dead" brush cutters aren't broken — they just have stale fuel or a dirty plug/filter. Good fuel and a clean filter prevent 90% of problems.

Struggling to start it? See our starting guide.

Four-stroke engines

Four-strokes such as Honda's GX25 and GX35 and Makita's MM4 engines have an oil sump instead of mixed fuel. Check the oil level before each use with the engine level, top up with the grade in the manual, and change it at the stated interval — the Honda UMK 425's sump holds just 0.08 L, so it doesn't take long to run low. Stihl's 4-MIX engines run on two-stroke mix and have no sump.

Cordless machines

  • Keep the battery contacts clean and dry, and charge in a dry place at room temperature.
  • Don't leave batteries in a hot car or a freezing shed.
  • Clean grass from the motor vents so the motor stays cool — brushless motors still need airflow.
  • Check the guard's line-cutting blade is sharp, so line is trimmed to the right length.

Gearbox, shaft and guard

Petrol and many cordless brush cutters have a bevel gearbox at the cutting end. Grease it at the interval in the manual — Stihl sells Superlub FS grease for its gearboxes. Check the shaft coupling on split-shaft machines is clean and tight, and replace a cracked guard immediately: it's there to stop thrown debris and the blade.

A simple seasonal checklist

  1. Start of season: fresh fuel, new or cleaned spark plug, clean air filter, check fuel lines and primer bulb for cracks.
  2. Every session: clean head and guard, check blade or line, check nuts and guard are tight.
  3. Every few sessions: clean the air filter, grease the gearbox if due.
  4. End of season: run fuel dry or switch to alkylate fuel, clean the machine, store batteries part-charged.

Spare parts such as primer bulbs, air filters and fuel hose kits are cheap and worth keeping in the shed.

Frequently asked questions

How often should I service a petrol brush cutter?

Clean the air filter and check the spark plug every few uses or once a season, and replace them yearly. Always use fresh fuel, and never store the machine with old fuel in the tank over winter.

How do I store a brush cutter over winter?

For petrol, either drain the fuel or run the carburettor dry — or use alkylate fuel that stores for years. Clean the machine, and store batteries part-charged in a cool, dry place.

Do cordless brush cutters need maintenance?

Very little — just keep the head and guard clean, replace worn line or blades, and store batteries correctly (part-charged, cool, dry). There's no engine to service.