Four Stroke Theory of Operation

Bottom Dead Center - BDC

The very bottom of the piston travel in the cylinder

Four Parts to Engine Operation

An small gas engine needs four things to run: 1. Air 2. Fuel 3. Spark 4. Compression

Camshaft Operation

During the four stroke cycle, the camshaft is operated off of the crankshaft. The Camshaft is in time with the crankshaft. The lobes on the camshaft push upwards on the tappets or pushrod, which push on the valve to open them.

Four Stroke Operation

The four stokes of an engine must happen in order. The four strokes do not have to start in order. During the four stroke cycle, the crankshaft makes two complete revolutions. During the four stroke cycle, the camshaft operates at 1/2 the speed, or makes one complete rotation.

Intake Stroke

The piston travels downward in the cylinder creating a vacuum that sucks in the air and fuel mixture. The intake valve is open. The exhaust valve remains closed.

Exhaust Stroke

The piston travels upward in the cylinder pushing out the burned air fuel mixture. The exhaust valve is open allowing the burned air fuel mixture to escape. The intake valve is closed

Compression Stroke

The piston travels upward in the cylinder. Both the intake and exhaust valve remains closed. The air and fuel mixture is compressed .

Power Stroke

The spark plug ignites the air fuel mixture. The piston is forced downward in the cylinder by the burning air fuel mixture. Both the intake and exhaust valves are closed.

Combustion Chamber

The uppermost part or the cylinder. The air fuel mixture is ignited and burned in this part of the cylinder.

Top Dead Center - TDC

The very top of the piston travel in the cylinder