How to replace a chainsaw bar and chain (UK guide)

What you will need

Gather these five things before you start. None of it is specialist kit.

• A replacement bar and chain matched to your saw, same pitch, gauge and drive link count as the original (check the old bar or your saw's manual, not just the bar length)
• Cut-resistant gloves
• The combination tool or spanner/screwdriver that came with your saw
• Bar and chain oil, topped up and ready
• A flat, stable surface to work on

Our Fit Check tool matches a task to the right power type, bar length and PPE tier for anyone still deciding what to buy rather than replace.

How to replace a chainsaw bar and chain

Work through these steps in order. The whole job is mechanical, not fiddly, and most of it is just making sure the chain goes on the right way round and comes out tensioned correctly.

1. Make it safe. Switch the saw off and let it cool if you've been running it, remove the battery or the spark plug lead so it cannot start, and put on cut-resistant gloves before you touch the bar or chain.
2. Release the chain brake and open the side cover. Push the front hand guard forward to release the chain brake, then use the combination tool that came with your saw to loosen and remove the nuts holding the side cover in place.
3. Remove the old bar and chain. Lift the side cover away, slide the worn bar forward off the bar studs to free it from the tensioning pin, then lift the bar and chain off together and set the old chain aside.
4. Fit the new bar and chain. Slide the new bar onto the bar studs. Loop the new chain around the drive sprocket first, then feed it into the bar's guide groove, keeping the cutters facing forward along the top of the bar, not backward.
5. Refit the side cover loosely. Put the side cover back on and start the retaining nuts by hand. Leave them loose for now. The bar still needs to move freely for the next step.
6. Tension the chain. Turn the tensioning screw, or the adjuster wheel on tool-less models, until the chain sits snug against the underside of the bar. A correctly tensioned chain lifts roughly 3mm off the bar when pulled gently by hand and still turns freely with no binding.
7. Tighten the side-cover nuts fully. Hold the bar tip up, tighten the side-cover nuts fully with the saw's tool, then check once more that the chain still pulls round the bar by hand without binding.
8. Check the chain oil before you cut. Top up the chain oil reservoir if it is low. A new chain and bar groove need lubrication from the very first cut. Never run a freshly fitted chain dry.

Chain tensioning: how tight is right

Tension is the step most people get wrong, in both directions. A chain that is too loose can jump the bar or derail mid-cut. A chain that is too tight drags, wears the bar groove and drive sprocket faster, and puts extra load on the clutch and chain brake.

A properly tensioned chain sits close against the underside of the bar but still lifts a few millimetres, roughly 3mm, when you pull it gently away by hand, and it pulls round the full length of the bar smoothly with no tight spots. Treat that 3mm lift as a working rule, not an exact spec. Exact tension specifications vary by saw model, especially between older screw-tensioned bars and newer tool-less systems. Check the manual or the manufacturer's own guidance for the precise figure on your saw, for example Stihl UK or Husqvarna UK, the authoritative source for your exact model.

A new chain also stretches slightly in its first few cuts as it beds in. Check tension again after the first tank of fuel or first battery charge, and retighten if it has gone slack.

Keeping the chain sharp between changes

This bar-and-chain job is also the point to think about sharpening. A blunt or mistensioned chain is a common reason people end up here in the first place. Chains dull faster in dirty or knotty wood, and fastest of all when the bar tip so much as grazes soil, a stone, or a fence staple buried in a log. That kind of contact takes the edge off every cutter in a single pass.

The basic idea behind filing is straightforward, even if the tool feels fiddly at first. Each cutter has a top plate that needs to stay at a consistent angle, roughly 30 degrees off square to the bar on most chains, filed from the inside of the cutter outward. A round file held at that angle, with a few consistent strokes per cutter, keeps the chain cutting straight rather than pulling to one side. Manufacturer guides such as Stihl UK's and Husqvarna UK's cover the exact file size and angle for your specific chain, and both vary by chain pitch.

Sharpness is only half the story though. A blunt or badly tensioned chain is a real cause of poor, ragged cuts and of kickback risk. A chain that will not bite cleanly tends to bounce or grab instead of cutting through. Check tension every time you sharpen, not just when you fit a new chain.

This kind of hands-on maintenance matters most for petrol chainsaw owners. Felling and heavy firewood work blunts and stretches a chain far faster than occasional trimming with a lighter cordless saw.