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Buy Outboard Parts LOWER UNITS
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The lower unit is the gearcase assembly that transfers power from the powerhead
to the propeller while allowing steering and trim.
CRITICAL COMPONENTS:
Gearcase: Cast housing containing the gear set. Must remain free of cracks,
corrosion, and impact damage. A damaged gearcase often requires full replacement.
Water Pump Impeller: Located in the upper portion of the lower unit. Pumps
cooling water through the engine. Should be replaced every 1-2 seasons or
immediately if overheating occurs. Signs of failure include weak telltale
stream or no water discharge.
Drive Shaft: Connects the powerhead to the gear set. Splines must be clean
and greased during installation to prevent wear.
Propeller Shaft: Output shaft the prop mounts to. Can be bent by prop strikes.
A bent shaft causes vibration and seal failure.
Skeg: The fin below the prop. Protects the prop and aids steering. A broken
skeg can be repaired with bolt-on skeg guards or professional welding.
Shift Shaft: Transmits gear selection from the remote control to the gears.
COMMON ISSUES:
Water Intrusion: Milky or creamy gear oil indicates water mixing with oil.
Caused by failed seals (prop shaft, driveshaft, or shift shaft). Running with
water in the gearcase destroys bearings and gears rapidly.
Impact Damage: Striking submerged objects can bend the prop shaft, crack the
gearcase, or break the skeg. Always inspect thoroughly after any strike.
Corrosion: Especially problematic in saltwater. Anodes (sacrificial zincs)
must be inspected regularly and replaced when 50% depleted.
MAINTENANCE SCHEDULE:
Before Each Season: Check gear oil level and condition. Remove the lower
drain screw—oil should flow freely. If milky, pressure test and reseal.
Annually: Drain and replace gear oil. Use manufacturer-specified oil (usually
high-viscosity marine gear lube). Inspect anodes. Check water pump operation.
Every 100 Hours or 2 Years: Replace water pump impeller, inspect housing for
wear, replace thermostat.
TROUBLESHOOTING:
Noise: Grinding or whining in gear indicates worn bearings or gears. Clunking
when engaging gear may be normal but excessive noise requires inspection.
Overheating: Often caused by failed impeller, blocked water intake, or
thermostat stuck closed.
Difficulty Shifting: May indicate shift shaft adjustment issues, worn clutch
dog, or cable problems.