How do I replace the blade on my Petrol Lawnmower

This guide explains how to safely remove and replace the cutting blade on a petrol lawnmower.

Table of Contents

1. Tools and Parts Required
2. Preparing the Lawnmower
3. Removing the Blade
4. Fitting the New Blade
5. Important Notes

Tools and Parts Required

Before starting, ensure you have the following:

• Thick protective gloves
• Socket wrench (appropriate size for blade bolt)
• New blade washer (recommended to replace the old washer)

Preparing the Lawnmower

Before carrying out any work:

1. Switch off the engine completely.
2. Remove the spark plug cap to prevent accidental starting.
3. Ensure the mower is on a stable surface.

Accessing the Blade

You can access the blade in one of the following ways:

• Tilt the mower backwards by lowering the handles (ideally with assistance), or
• Drain all fuel and oil, then carefully turn the mower upside down

Important: Ensure fuel and oil are fully drained before inverting the machine.

Removing the Blade

Step 1 – Secure the Blade

Wear thick gloves and firmly hold the blade to prevent it from rotating.

Step 2 – Loosen the Blade Bolt

Using a socket wrench:

• Turn the blade bolt anti-clockwise to loosen it

If the bolt is tight:

• Use a block of wood to stop the blade from turning, or
• Clamp the blade carefully to secure it in place

Step 3 – Remove the Blade

Once loosened:

• Remove the bolt and washer
• Take off the blade from the blade adaptor / boss / carrier

Fitting the New Blade

Step 1 – Inspect the Blade Adaptor

Check the blade adaptor for damage.

If it is cracked, worn, or damaged, it should be replaced before fitting a new blade.

Step 2 – Fit the New Blade

1. Position the new blade onto the adaptor.
2. Ensure the locating pins are correctly aligned.
3. Make sure the blade is seated securely and evenly.

Step 3 – Fit New Washer and Bolt

• Install a new washer (do not reuse the old one)
• Insert the blade bolt

Step 4 – Tighten the Blade Bolt

Using the socket wrench:

• Tighten the bolt clockwise
• Ensure it is securely fastened

Important Notes

• Always replace the washer when fitting a new blade
• Never operate the mower with a damaged or loose blade
• Ensure the blade is fitted in the correct orientation

If the Blade Bolt Will Not Loosen

If the blade bolt is stuck:

• Secure the blade using a block of wood
• Apply controlled force using the correct socket tool
• Avoid damaging the blade or adaptor