How 4-Cycle Engines Work

Wondering how a small engine works? This video details how Briggs & Stratton 4-cycle engines work to maximize power to your lawn mowers & outdoor equipment.

At Briggs & Stratton, our 4-cycle engines are the world leader for production and quality. This is due to the 4-stroke overhead valve engine system. It maximizes the power by your Briggs & Stratton engine to increase performance for your lawn mower or other outdoor power equipment.

The 4-Cycle Engine Process

  • Step 1: Intake Stroke
    During the intake stroke, air and fuel are filtered through the carburetor into the piston as the intake valve opens. The valve closes, cutting off the air-fuel fixture, when the piston reaches the bottom of its stroke.
  • Step 2: The Compression Stroke
    Now that the fuel is in the compression chamber, the engine maximizes the power it will create by compressing that fuel into a smaller space. The piston rotates back up its top point, trapping the air-fuel mixture between piston and cylinder head. Briggs & Stratton engines are designed for efficiency by maximizing compression during this step in the 4-cycle engine process.
  • Step 3: The Power Stroke
    Now that the air-fuel mixture is compressed, it’s time to add a spark. The ignition coil creates a high voltage that is discharged in the chamber by the spark plug. Once the air-fuel mixture is lit, the hot air forces the piston back down the cylinder.
  • Step 4: The Exhaust Stroke
    The final step in this 4-cycle engine process is the exhaust stroke. The exhaust valve opens as the piston pushes the spent gases out of the chamber. Once that is complete, the exhaust valve closes and the intake valve opens to start the process over again.

Each repetition of the cycle requires two rotations of the crankshaft. Wonder how the small engine keeps working when only 1 of the 4 strokes creates power? During the power stroke, the flywheel is given a push. The momentum behind that and inertia keep it moving between power strokes.