How to service a petrol lawnmower

Written by steven douglas
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How to service a petrol lawnmower
Homeowners can service their own mowers in a couple of hours. (mower image by Tomasz Wojnarowicz from

Servicing a walk-behind lawnmower with a gasoline (petrol) engine consists of a series of similar steps regardless of the year or model of the mower being serviced. This is primarily because all major lawnmower manufacturers use the same basic technology to get the job done. Most homeowners can completely service their machines with regard to routine or annual maintenance items in under two hours using simple hand tools.

Skill level:

Things you need

  • Spark plug wrench
  • SAE or metric socket set
  • Replacement spark plug (specific to make and model)
  • Fuel stabiliser/carburettor cleaner additive
  • Oil drain pan
  • Clean rags
  • Engine oil (make and model specific)
  • Replacement drive belt (specific to make and model)
  • Pliers
  • Screwdrivers set (Phillips and slotted)
  • Light machine oil
  • Painter's putty knife

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  1. 1

    Park the mower on a flat, level surface, and disconnect the spark plug wire from the spark plug to prevent accidental starting of the engine. Remove the spark plug with a spark plug wrench, and replace the plug with a new one. Tighten the new spark plug 1/4 turn with the wrench after hand-tightening it. This should be performed every 100 hours of engine operation.

  2. 2

    Add a fuel stabiliser/carburettor cleaner additive to the gas tank per the specifications on the bottle. Remove the engine oil drain plug with a socket, and drain the engine oil into an oil drain pan. Install the engine oil drain plug and tighten it. Refill the engine with fresh oil per the manufacturer's recommendations. Engine oil should be changed every 50 hours of engine operation.

  3. 3

    Replace the air filter every 50 hours of engine operation. This is done by removing the air filter cover (usually with a Phillips screwdriver), then pulling the dirty filter free from its compartment in front of the carburettor.

  4. 4

    Use a socket wrench to remove the cutting blade by removing the bolt (or bolts) that secure the blade to the engine driveshaft. Tilt the mower on its side to gain access to the blade. Blades should be replaced if they show signs of chipping (causes the blade to become unbalanced), but they may be sharpened if they are still in good shape. This should be performed every 100 hours of engine operation.

  5. 5

    Check the drive belt for wear or damage if your mower is self-propelled, and replace it according to your manufacturer's instructions, if necessary. Clean any debris build-up from the underside of the mowing deck with a painter's putty knife. Check the grass trail shield at the rear of the mower for wear or damage. Retighten it if necessary. This should be performed every 25 hours of engine operation.

  6. 6

    Check your grass bag and grass discharge chute for wear or damage. Tighten attaching components as necessary. Check the drive wheels and roller wheels for excessive wear or damage, and lubricate them on their axles with light machine oil. This should be performed every 25 hours of engine operation.

  7. 7

    Inspect all control cables, drive cables, operator control bars and speed control levers for smooth action. Lubricate the cables with light machine oil. Tighten all cable connections and mounting hardware. This should be performed every 25 hours of engine operation.

Tips and warnings

  • Always use original equipment manufacturer (OEM) replacement parts when available.

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