A chain saw does not cut with force. It cuts with sharpness. If you are pushing hard to make the saw go through wood, the chain is blunt, and pushing harder wears the bar, loads the engine and makes the saw far more dangerous to hold.
Three things keep a saw working: chain tension, sharpness and oil.
Chain tension
Too loose and the chain can jump off the bar, which is one of the more dangerous failures on a saw. Too tight and it binds, overheats and stretches, and it will wear the bar rails and the sprocket quickly.
Set it with the engine off and the chain cool. Lift the chain at the middle of the bar — the drive links should stay in the bar groove but the chain should lift slightly clear. You should be able to pull it around the bar by hand (wearing a glove) without it feeling stiff.
New chains stretch. Check tension after the first few cuts on a new chain, then regularly through the day. Always re-check after the saw cools, because a chain tensioned hot will be too tight when cold.
Sharpening
You can sharpen a chain many times before it needs replacing, and doing so is the single biggest thing you can do for cutting speed.
- Use a round file of the diameter your chain requires. The size is specific to the chain pitch — using the wrong size changes the cutting geometry.
- Hold the correct top-plate angle, commonly around thirty degrees for general cross-cutting. A file guide makes this far easier to hold consistently.
- File from the inside of the tooth outwards, on the push stroke only, lifting on the return.
- Give every tooth the same number of strokes. Uneven teeth make the saw pull to one side and cut a curved kerf.
- Do not forget the depth gauges. The small rakers ahead of each tooth control how deep the tooth bites. As teeth are filed back, the rakers become proportionally too high and the saw stops cutting even though the teeth are sharp. Check them with a depth gauge tool every few sharpenings.
Signs a chain needs sharpening: it produces fine dust instead of chips, it needs downward pressure to cut, it cuts at an angle, or it smokes in the cut.
Bar oil
The chain runs on a film of oil along the bar. Without it, the chain and bar overheat and destroy each other within minutes.
Use proper chain and bar oil. It is formulated to be tacky enough to stay on a chain spinning at speed, which ordinary engine oil is not. Used engine oil is a false economy — it is thin, it carries abrasive particles and it throws off the chain.
Fill the oil tank every time you fill fuel. A rough check that the oiler is working: run the saw at speed with the bar tip pointing at a light-coloured surface a few inches away, and you should see a fine line of oil thrown off.
Bar care
- Clean the bar groove regularly — packed sawdust blocks the oil holes.
- Check the oil holes at the base of the bar are clear.
- Turn the bar over periodically so both rails wear evenly.
- File off any burr on the rail edges.
- Replace the bar if the rails are uneven, spread or badly worn, or if the chain can rock sideways in the groove.
The sprocket
The drive sprocket wears in step with the chain. Running a new chain on a badly worn sprocket wears the new chain quickly. As a rule, expect to replace the sprocket after a couple of chains, and inspect it whenever you fit a new chain.
Engine care
Most chain saws are two-stroke, so fuel mixing discipline matters as much as it does on a brush cutter. Mix to the ratio in your manual, measure rather than estimate, use proper two-stroke oil, mix small quantities and label the can clearly.
Clean the air filter daily in dusty or dry conditions. Clear sawdust off the cooling fins and out of the starter housing — a saw packed with sawdust overheats.
Safety points that are not optional
Kickback is the main hazard: the bar tip touching wood can throw the saw back towards the operator violently. Keep the chain brake working, never cut with the tip, keep both hands on the saw with thumbs wrapped, and stand slightly to the side of the cutting line rather than directly behind it.
Wear eye and ear protection, gloves, and cut-resistant leg protection. Never cut above shoulder height, and never on a ladder.
See the chain saw range and the petrol chain saw models, or spare parts for chains, bars and service items.