COMPRESSION stroke: with both intake and exhaust valves closed, the piston returns to the top of the
cylinder compressing the air, or fuel‐air mixture into the combustion chamber of the cylinder head.
Detail
Piston moves from BDC to TDC
Intake valve closed
Exhaust valve closed
Piston movement reduces the volume of the combustion chamber‐‐increases pressure.
Pressure of compression = 60 to 80 psi.
Any pressure that escapes reduces the performance of the engine.
360 degrees of rotation