How do I replace the blade tension assembly on my Petrol Chainsaw

Quick Answer

If your petrol chainsaw chain will no longer tighten or loosen correctly, the chain tensioner assembly may be worn or damaged. Replacing the assembly will restore the chain tensioning function, provided it is fitted correctly and the guide bar and chain are in good condition.

⚠️ Safety Notice

Before carrying out any maintenance:

• Switch off the chainsaw and allow it to cool completely.
• Remove the spark plug cap to prevent accidental starting.
• Wear suitable protective gloves when handling the guide bar and chain.
• Work on a clean, stable surface.

When Does the Tensioner Assembly Need Replacing?

You may need to replace the chain tensioner assembly if:

• The chain cannot be tightened or loosened correctly.
• The tensioning knob no longer engages with the mechanism.
• The chain remains loose despite adjusting the tension.
• The side cover or chain brake housing is damaged.
• The tensioning mechanism is worn, broken, or missing parts.

The tensioner assembly is usually located behind the side cover and may form part of the chain brake housing, depending on your model.

Before You Begin

The design of the tensioner assembly varies between chainsaw models.

Always refer to your product's user manual or parts diagram to ensure you have the correct replacement part and understand how it is fitted.

Replacing the Tensioner Assembly

1. Ensure the chainsaw is switched off and fully stopped.
2. Disengage the chain brake.
3. Loosen the chain tension and remove the side cover by undoing the retaining knob or nuts.
4. Remove the guide bar and chain if necessary to gain access to the tensioner assembly.
5. Remove the existing tensioner assembly.
6. Inspect the mounting area and remove any dirt, sawdust, or debris.
7. Position the new tensioner assembly, ensuring it aligns correctly with the guide bar adjustment pin and mounting points.
8. Refit the guide bar and chain.
9. Reinstall the side cover and tighten it loosely.
10. Adjust the chain tension until the chain sits snugly against the guide bar but can still be pulled around by hand while wearing gloves.
11. Fully tighten the side cover once the correct chain tension has been achieved.

After Reassembly

Before using the chainsaw:

• Check that the chain moves freely around the guide bar.
• Confirm the chain brake operates correctly.
• Ensure all fixings are securely tightened.
• Run the chainsaw briefly and recheck the chain tension, adjusting if necessary.

If the Problem Persists

If the chain still cannot be tensioned correctly after replacing the tensioner assembly:

• Check the guide bar for excessive wear or damage.
• Inspect the chain for wear or stretching.
• Ensure the tensioner adjustment pin is correctly engaged with the guide bar.
• Contact our Technical Support Team for further assistance if the problem continues.

Frequently Asked Questions

Why won't my chainsaw chain tighten?

The most common causes are a worn or damaged tensioner assembly, a stretched chain, or a worn guide bar.

Do I need to remove the chain to replace the tensioner assembly?

On most models, yes. Removing the guide bar and chain provides access to the tensioner assembly.

Why is the chain still loose after replacing the tensioner?

Check that the tensioner adjustment pin is correctly engaged with the guide bar and inspect the guide bar and chain for wear.

Should the chain be tight after adjustment?

No. The chain should sit firmly against the guide bar but still move freely by hand when wearing protective gloves.