gearhead

/ˈɡɪrˌhɛd/
noun
  1. A person who is very interested in cars, machines, or technology.
    • The car show was full of gearheads admiring the engines.
    • My uncle is a real gearhead; he spends every weekend working on his vintage Mustang.
    • She's a gearhead who loves building custom computers.
  2. The part of a machine that contains the gears, especially in a motor or engine.
    • A faulty gearhead can cause the machine to make a grinding noise.
    • The robot's gearhead allows its arm to move smoothly.
    • The mechanic replaced the damaged gearhead in the drill.