You are holding a machine that punches well above its weight class. A standard 16-inch chainsaw looks simple, but the heart of the operation is a compact two-stroke gasoline engine that generates roughly 3 horsepower. That is nearly one horsepower for every pound of engine weight. How does it do that? By stripping away the heavy parts you find in cars and lawnmowers.
The cutting bar is 16 inches long, or about 40.6 centimeters. The chain runs in a groove around this bar, with sharp cutting teeth spaced along its length. But the bar is just the stage. The action happens inside the engine.
The Air-Cooled Two-Stroke Advantage
This engine displaces 3 cubic inches, which converts to 49 cubic centimeters. It weighs just 4 pounds, or 1.8 kilograms. The secret to this low weight is the cooling system. It is air-cooled.
Cars need radiators. Lawnmowers often need water jackets. This chainsaw needs neither. It relies on airflow over the cylinder fins to dissipate heat. This eliminates the radiator, water pump, and coolant weight. The result is an engine that is incredibly light for the power it produces.
The engine is a two-stroke design. This means it has no valves or cams. It generates power on every rotation of the crankshaft. A four-stroke engine only fires once every two rotations. The two-stroke design effectively doubles the power output for the same displacement. That is why a small 49 cc engine can cut through hardwood with ease.
How the Chain Moves
The chain is driven by a centrifugal clutch. This is a simple but effective mechanical link between the engine and the bar. When the engine is idling, the clutch is disengaged. The chain stays still even if the engine is running. This is a critical safety feature.
When you squeeze the throttle, the engine speeds up. Inside the clutch, centrifugal plates spin outward. They engage with the clutch drum. Now the chain begins running. The speed of the chain matches the engine speed. Release the throttle, and the plates retract. The clutch disengages. The chain stops.
Fuel and Oil Systems
The engine draws in a mixture of gas and oil. The carburetor mixes these with air and draws the fuel into the engine using crankcase vacuum. The gas tank holds about one pint, or 0.5 liters. You must mix two-stroke engine oil with the gasoline before filling the tank. This oil lubricates the internal moving parts.
There is a separate system for the chain itself. A small oil pump draws chain oil from its own reservoir. This oil coats the chain and bar, preventing binding and reducing friction. Do not confuse the two lubrication systems. The gas-oil mix feeds the engine. The chain oil feeds the bar and chain. Both are essential. If you run the chain oil tank dry, the bar will overheat and the chain will bind. If you run the gas tank dry, the engine seizes.
Ignition and Exhaust
Ignition is handled by a magneto connected to a spark plug. The magneto generates the high voltage needed to create a spark in the combustion chamber. There is no battery. No alternator. Just a
