A mechanism that controls timing; specifically (in an internal-combustion engine) the mechanism by which the valves are made to open and close at the right time.
Origin
Late 19th century; earliest use found in Outing.
Definition of timing gear in US English:
timing gear
noun
Engineering
A mechanism that controls timing; specifically (in an internal-combustion engine) the mechanism by which the valves are made to open and close at the right time.