Guide to Outboard Parts

Beginners Guide to the main components of an Outboard Engine


Guide to Outboard Engine Parts

New to Outboard Engines? Here's our  beginners guide to the main components and what they do.

Outboard Engine

Not all outboards will have all of these componets (e.g. Power Trim switch) but for most outboards will have the following:

    • Motor Cover or 'Cowling' - U/V resistent plastic cover desgined to protect the main engine compartment from the elements. And yourself from the engine and all that heat and electrics.
    • Power Trim or Tilt Switch - Mechanical lever to adjust the rake angle of the outboard in the water depending on the tender or boat hull design in order to maximise the efficiency of the engine thrust being placed into the water by the propeller.
    • Pilot Water Hole - Most outboard engines are cooled by permanently pumping water around the main engine block and head. (just like a car). But outboards are an 'open' cooling system so unlike your car instead of the same water being pumped round in a sealed circuit outboards just pump the heated water and dump it back in the water. The exit point for this cooling circuit is call the Pilot Water Hole.
    • Flush Plug - On larger outboards there will be a special opening for 'flushing' the water cooling circuit.
    • Engine Oil Drain Plug - Pretty self-explanatory really. 4-stroke outboards that are lubricated through a fuel/oil mix like 2-stroke (more - differences between 2-stroke and 2-stroke) engines require oil to maintain engine lubrication. Just like your car this oil needs to be changed periodically and as such necessitates an Engine Oil Drain Plug.
    • Clamp Bracket - A large u-shaped bracket usually with 2 sides that is used to attach the outboard to the stern or transom of your rib or hull. This bracket usually incorporates a small pin that can be moved into one of half a dozen holes in order to finely tune the engine angle into the water.

  • Anode(s) - Take many formms and are often absent on smaller and older outboards essentially an anode is a piece of metal designed to be the softed or 'least path of resistence' for electrical current leeching out of the outboard. It is a called a 'sacrificial' anode as it slowly wears down over time.  Usually replaced every few years. Anodes come in different metals and strengths depending on need.
  • Anti-Cavitation Plate - Cavitation is a hydro-dynamic phenomenon where the propeller thrust reduces water pressure around it allowing air to get pulled into the space. This cavitation reduces the efficiency and performance of the outboard hence manufacturers incorporate a metal plate above the propeller to reduce the impact of cavitation.
  • Trim Tab - not really a component as there's not serviceable element to it but simply a moulding on the back of the anti-cavitation plate designed to aid steering performance.
  • Gear Oil Level Plug - All outboards have a gearing at the bottom of the drive shaft to transfer the energy through 90 degress into the shaft the propeller is attached to. This gearing is enclosed in the gear case (the bulb shape just behind the propellor) which is lubricated with a special type of high-temperature gear oil. The level of oil is checked and topped up by opening the gear oil level plug. Typically the gear oil should be flush or 'level' with this opening.
  • Gear Oil Drain Plug - The exit point for the gear oil for when it needs changing. Like most oils gear oil should be changed according to the manufacturers  guidelines - usually number of engine hours or period of time.
  • Water Intake Hole - Small hole in the gear case for fresh (or salt!) water to enter the cooling jacket. Sometimes incorporating a fine mesh filter to stop the ingest of dirt and plant material.

Fuel Tank

Outboard Fuel Tank Components

Small outboards (2-5HP) will have an internal fuel tank, i.e. a small plastic container sitting alongside or above the engine and hidden under the cover.  Larger outboards that consume more fuel will have an external tank giving longevity and range to your days on the water.  These are typically 10 or 15 litre tanks that connect to an Fuel line port on the front of the outboard with a locking clip. They have:

  • Air-vent Screw - A small screw or valve, usually plastic that should be loosed to allow to enter the tank when the outboard is running but closed (to restrict fuel fumes) when not in use.
  • Fuel Hose - Non-perishable plastic line connecting the tank to the outboard fuel line port. Normally incorporating plunger clip to secure it.
  • Priming Bulb - Small hollow plastic bulb used to 'prime' the fuel line when it's first connected to the outboard.  This needs to be squeezed several times after connecting the fuel line but before starting the outboard to ensure fuel and not air is entering the engine when it's first started.

If you're having starting problems or poor running issues check out our post on two stroke outboard fuel problems

Enjoy the water and be safe with your boating!