My Petrol Chainsaw will not tension the chain correctly

If you cannot tension the chain on your petrol chainsaw, the cause is often an incorrectly fitted guide bar, a misaligned tensioner pin or the chain brake being engaged. Correct chain tension is essential for safe operation, efficient cutting and reducing wear on the guide bar and chain.

This guide explains the checks you can carry out to correctly tension the chain on your petrol chainsaw.

Quick Answer

If your chainsaw chain will not tension correctly:

• Ensure the chain brake is disengaged.
• Loosen the guide bar nuts.
• Check that the tensioner pin is correctly located in the guide bar.
• Adjust the chain tension using the tensioning screw.
• Hold the guide bar nose upwards while tightening the bar nuts.
• Confirm the chain lifts slightly from the guide bar but remains seated in the guide groove.

If the chain still cannot be tensioned, inspect the guide bar, chain and tensioning mechanism for wear or damage.

Before You Begin

Before adjusting the chain tension:

• Switch off the engine and allow it to cool completely.
• Engage the chain brake while transporting the chainsaw, then disengage it before making the adjustment.
• Remove the spark plug cap where practical.
• Wear suitable personal protective equipment (PPE), including protective gloves.
• Place the chainsaw on a stable, level surface.

Always refer to your instruction manual, as the chain tensioning system may vary between models.

Steps

Step 1 – Disengage the Chain Brake

Before adjusting the chain tension, ensure the chain brake is fully disengaged.

Attempting to tension the chain with the brake engaged can prevent the guide bar from moving correctly and lead to incorrect adjustment.

Step 2 – Loosen the Guide Bar Nuts

Using a suitable spanner:

1. Loosen the two guide bar nuts.
2. Do not remove them completely.

The guide bar should now be able to move slightly during adjustment.

Step 3 – Check the Tensioner Pin

Inspect the tensioner pin and ensure it is correctly located in the adjustment hole on the guide bar.

If the pin is not engaged correctly, the tensioning screw will not move the guide bar and the chain cannot be tensioned properly.

Step 4 – Adjust the Chain Tension

Turn the chain tensioning screw until the chain fits correctly around the guide bar.

While adjusting:

• Lift the nose of the guide bar upwards.
• Continue adjusting until the chain sits snugly in the guide bar groove.

The chain should move freely by hand without excessive slack.

Step 5 – Tighten the Guide Bar Nuts

While continuing to support the nose of the guide bar:

1. Tighten both guide bar nuts securely.
2. Recheck the chain tension after tightening.

The chain should remain correctly tensioned once the guide bar is secured.

Step 6 – Check the Chain Movement

Pull the chain carefully around the guide bar while wearing protective gloves.

The chain should:

• Move smoothly around the guide bar.
• Lift slightly away from the guide bar when pulled.
• Return into the guide groove when released.

If the chain is excessively tight or loose, repeat the adjustment.

Frequently Asked Questions

Why won't my chainsaw chain tighten?

The most common causes are an engaged chain brake, a tensioner pin that is not seated correctly, a worn chain, a worn guide bar or a damaged chain tensioning mechanism.

How tight should a chainsaw chain be?

A correctly adjusted chain should sit firmly in the guide bar groove while still moving freely by hand. When pulled upwards, the drive links should lift slightly from the guide bar but remain engaged within the groove.

Should I lift the guide bar while tightening the nuts?

Yes. Supporting the nose of the guide bar while tightening the guide bar nuts helps ensure the correct chain tension is maintained during operation.

Why does my chain become loose after tightening?

A chain may loosen if the guide bar nuts were not tightened securely, the chain has stretched through normal use or the tensioning mechanism is worn.

Can I use my chainsaw if the chain will not tension correctly?

No. A loose or incorrectly tensioned chain can derail during operation and create a serious safety hazard. Always correct the problem before using the chainsaw.

What should I do if I still cannot tension the chain?

Inspect the guide bar, chain, tensioner pin and chain tensioning mechanism for damage or excessive wear. Replace any faulty components before operating the chainsaw.