Valve Mechanism

A valve mechanism is a group of components that
opens and closes the intake and exhaust valves in
the cylinder head at the appropriate timing.
Crankshaft
Timing sprocket
Timing chain
Intake camshaft
Intake valve
Exhaust camshaft
Exhaust valve
* The diagram shows a VVT-i system valve
mechanism.

Intake stroke

The exhaust valve closes and the intake valve
opens. The downward stroke of the piston causes
the air-fuel mixture to be drawn into the cylinder
from the open intake valve

Exhaust stroke

The exhaust valve opens as the piston is about to
complete its downward stroke. Then, the exhaust
gases that result from the combustion are
discharged outside of the cylinder