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Outboard Lower Units

Written by Nicholas Kamuda
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Many boaters will have to make repairs to their outboard lower units at some point. The lower unit is half of an outboard engine, and is responsible for propulsion and cooling, among other things. Though for many engines, the outboard lower units are strong and well engineered, they contain many complex engine components that need to be periodically maintained and repaired.

The propulsion from an engine comes from its propeller. The propeller spins on the prop shaft, which in turn is spun by the drive shaft. Much of the engine tuning process involves carefully selecting and adjusting the propeller. As such, the propeller and rest of the propulsion system are often subject to scrutiny, attention, and tinkering.

Much of an outboard engine's cooling system is also housed in the outboard lower units. The intake and water pump, both reside there, near the propeller. The intake consists of a series of small holes, which allow water in but keep rocks and dirt out. The water pump's primary mechanism is a hearty rubber impeller. You may find that it's a good idea to keep both the impeller and the intake under a watchful eye, as they have a direct effect on your engine's output.

Purchasing Outboard Lower Units

Whole lower unit parts and kits are available at many marine parts suppliers. Online boating supply store and engine specialty stores also have a wide selection of many lower units, including those for older engines that are no longer available directly from the manufacturer, such as OMC engines. The service manual or parts catalog for your engine can tell you exactly what type of lower unit is compatible with your engine.

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