unic - valv
- unicycle
- unidirectional flow scavenging
- Unified National Coarse thread
- Unified National Fine thread
- uniflow scavenging
- uniform corrosion
- union nut
- unit
- unit body
- unit construction
- unit engine
- unitary construction
- unitary system
- united States Council for Automotive Research
- unitized construction
- unitized transmission
- universal
- universal Japanese Motorcycle
- universal joint
- universal joint socket
- universal motor
- universal spark plug socket
- universally jointed shaft
- unladen weight
- unleaded gas
- unleaded gasoline
- unloaded radius
- unloader
- unloader valve
- unmanned machinery spaces
- unobtanium
- unseating
- unsprung mass
- unsprung weight
- up-stroke
- updraft carburetor
- updraught carburetor
- uph
- upholstery
- upper ball joint
