How do I check the height adjustment is working on my Petrol Lawnmower

If your petrol lawnmower will not adjust its cutting height or the height adjustment lever does not lock into position, there may be a problem with the adjustment mechanism. This could be caused by a disconnected linkage, damaged spring or worn adjustment components.

This guide explains how the height adjustment system works and the checks you can carry out to ensure it is operating correctly.

Quick Answer

If the height adjustment on your petrol lawnmower is not working correctly, check the following:

• The height adjustment lever moves freely through its full range.
• The lever locks securely into each height position.
• The height adjustment spring is fitted and providing tension.
• The connecting rod is securely attached and undamaged.
• The front and rear axle linkages move together when the lever is operated.

Most height adjustment issues are caused by a disconnected linkage, damaged spring or worn adjustment mechanism.

Before You Begin

Before inspecting the mower:

• Switch off the engine and allow it to cool completely.
• Remove the spark plug cap to prevent accidental starting.
• Place the mower on a level surface.
• Wear suitable personal protective equipment (PPE), including gloves.
• Remove any grass or debris from around the wheel assemblies and adjustment mechanism.

If the mower has recently been used, allow all moving parts to cool before carrying out any checks.

Steps

Step 1 – Check the Height Adjustment Lever

Operate the height adjustment lever through its full range of movement.

Check that the lever:

• Moves smoothly.
• Has consistent resistance throughout its travel.
• Does not stick or bind.
• Allows the wheels to move between cutting heights.

If the lever is difficult to move, inspect the mechanism for dirt, corrosion or damage.

Step 2 – Check the Lever Locking Mechanism

Move the lever into each cutting height position.

Ensure that it:

• Locks securely into each notch.
• Does not slip out of position.
• Remains firmly engaged during movement.

If the lever will not lock, inspect the locking mechanism and adjustment spring for damage or wear.

Step 3 – Inspect the Height Adjustment Spring

The height adjustment spring provides the tension required to keep the lever securely engaged.

Inspect the spring and check that it is:

• Present.
• Correctly fitted.
• Not stretched.
• Not broken.
• Not detached from its mounting points.

Replace the spring if it is damaged or missing.

Step 4 – Inspect the Connecting Rod

The connecting rod links the front and rear axle assemblies, allowing all wheels to adjust together.

Locate the connecting rod, typically fitted along one side of the mower deck between the front and rear axles.

Check that the rod:

• Is securely attached at both ends.
• Is straight and free from damage.
• Moves correctly when the height adjustment lever is operated.

A bent or disconnected rod can prevent the height adjustment system from operating correctly.

Step 5 – Inspect the Connection Points

Inspect the fixing points where the connecting rod attaches to the front and rear axle assemblies.

Depending on the mower model, check that:

• Cotter pins are fitted securely.
• Spring clips are present.
• Nuts and bolts are tight.
• There are no worn or damaged mounting points.

Replace or tighten any loose or missing fixings before operating the mower.

Step 6 – Test the Height Adjustment

After completing the inspection:

1. Move the adjustment lever through every cutting height position.
2. Confirm that all wheels move together.
3. Check that each position locks securely.
4. Ensure the mower sits level on all four wheels.

The height adjustment system should now operate smoothly and hold the selected cutting height.

Frequently Asked Questions

Why won't my lawnmower height adjustment work?

The most common causes are a damaged adjustment spring, disconnected connecting rod, worn locking mechanism or loose linkage components.

Why won't the height adjustment lever stay in position?

If the lever slips out of its selected height, the adjustment spring may be damaged, missing or no longer providing enough tension.

What does the connecting rod do?

The connecting rod links the front and rear axle assemblies so that all wheels move together when the height adjustment lever is operated.

Can grass stop the height adjustment from working?

Yes. Grass clippings, dirt and debris can build up around the adjustment mechanism and restrict its movement. Cleaning the mechanism may restore normal operation.

Should all four wheels move together?

Yes. On most petrol lawnmowers with a central height adjustment system, operating the adjustment lever changes the height of both the front and rear wheels simultaneously.

Can I use my lawnmower if the height adjustment is damaged?

It is not recommended. A damaged adjustment mechanism can prevent the mower from maintaining a consistent cutting height and may lead to uneven cutting or further mechanical damage.