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What Is a Lower Unit (or Gearcase)? Understanding the Bottom Half of Your Outboard
The lower unit, sometimes called the gearcase, is one of the hardest-working parts of an outboard engine. It transfers power from the engine to the propeller and handles constant exposure to water, impact, and debris.
Even though it sits underwater, it plays a huge role in your boat’s overall performance and reliability.
What Does a Lower Unit Do?
The lower unit contains the gears, bearings, seals, and shafts that transfer engine power to the propeller.
It is responsible for:
Forward and
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May 20th 2026