The Hartzell MZ4222R is a 12 V aircraft starter assembly designed for fixed‑wing piston aircraft engines (especially Lycoming and similar series) that use a geared starter drive with 12 V electrical system and a specific tooth count/ring gear interface that meshes with the engine’s ring gear for cranking.

This starter unit is a robust geared starter, engineered to deliver high torque for reliable engine starts in aviation environments, with features such as:

12 V electrical operation for general aviation battery systems
Geared drive for enhanced torque suitable for large displacement engines
Designed to interface with the engine’s ring gear (often 149‑tooth/12/14 pitch)
Used as FAA‑approved replacement/remanufactured part in many piston aircraft installations
It’s often found as a replacement for older OEM starters with the same mounting and electrical interface — available as an overhauled unit with FAA paperwork where applicable.