The Stihl 039 mid-range chainsaw operates with a single piston, two-stroke gas-powered engine. Stihl manufactures the 039's engine to meet certain specifications for ignition timing, piston strokes and fuel ratios to maximize the engine's performance. These specifications help maintain optimum, factory level engine performance over the lifetime of the saw.
039 Engine Specs
The single piston, housed inside the cylinder's bore, creates 64.1 cubic cm of displacement. The piston bore is 49 mm and moves with a stroke of 34 mm. When idling, the engine should be set to 2,800 rpm and the clutch should automatically engage at 3,500 rpm. The highest speed, without load, the 039 can reach before damage is 12,500 rpm. Without the bar and chain, the engine weighs about 13 lbs. or 5.9 kg.
039 Ignition Specs
The electronic magneto ignition system uses an electric coil, housed inside a module, to build, hold and discharge the electricity needed to ignite the fuel inside the cylinder. To fire the spark, the flywheel needs to maintain a 0.15 to 0.3 mm air gap between the module arms and the flywheel magnets. The 039 chainsaw uses a Bosch WSR 6 F or NGK BPMR spark plug with an electrode gap of 0.5 mm.
039 Fuel Specs
The 039's fuel tank will hold up to 1.2 pints of mixed fuel. The fuel, when using Stihl brand two-stroke engine oil, needs to be mixed at a ratio of 50-to-1 gas to oil. However, when using another brand engine oil, the mix ratio should be between 32-to-1 and 40-to-1. The fuel is pulled into an all-position diaphragm carburetor. This style of carburetor uses an integral fuel pump which pulses, sending and delivering fuel with the crankcase's movements.
039 Cutting Specs
Stihl recommends using a reduced kickback bar on the 039 chainsaw. The bar can range in size from 16 to 20 inches. Stihl recommends using a 3/8 inch pitch chainsaw chain. This chain will pass over a seven tooth drive sprocket. Lubrication for the chain comes from an automatic piston driven oil pump. On the underside of this chainsaw, a manual oil knob will increase or decrease the output of oil, depending on the cutting requirements.