Outboard Motor Parts                         Manual

 Outboard motors are engines installed on boats to provide movement on water. They come in various types and power levels depending on the purpose and type of watercraft. The main function of an outboard motor is to convert fuel or electrical energy into the rotation of a propeller, which moves the boat forward or backward.

 

Main types of outboard motors:

  • Outboard motors – the most common type. They are mounted on the stern of the boat and can be either gasoline or electric-powered. Gasoline engines come in two-stroke and four-stroke varieties:
  • Two-stroke motors are lighter, simpler in design, and offer higher power-to-weight ratios. However, they are less eco-friendly and less fuel-efficient.
  • Four-stroke motors are heavier but more economical, quieter in operation, and produce fewer exhaust emissions.
  • Inboard motors – installed inside the hull of the boat. These are more powerful engines, commonly used on larger vessels, motorboats, and yachts. In this case, the propeller is connected to the engine via a shaft.
  • Electric motors – run on batteries and are ideal for small boats or bodies of water where gasoline engines are prohibited. They are quiet, eco-friendly, but limited in power and operational time.
  • Jet engines – often installed on speedboats and jet skis. They operate by ejecting water through a nozzle, allowing the boat to travel at high speeds.

How to choose an outboard motor:

  • Motor power should match the type of boat. For lightweight inflatable boats, motors up to 5 horsepower are sufficient, while for motorboats, engines of 20 horsepower or more are needed.
  • Fuel type: gasoline motors provide more power, but electric motors are more environmentally friendly and cheaper to operate.
  • Type of waterbody: in lakes or rivers where gasoline engines are banned, electric ones are preferable.
  • Frequency of use: for frequent long trips, a four-stroke engine is recommended, as it is more fuel-efficient.

Outboard motors play a key role in ensuring the mobility and functionality of watercraft, whether it's for fishing, sports, or leisurely boating.

Components of Outboard Motors

While not every outboard motor will include all of the following parts (such as the tilt trim switch), most will feature these key components:

 

Engine Cover or Hood

A UV-resistant plastic cover designed to shield the engine compartment from environmental elements and protect you from the heat and electrical components of the engine.

Tilt Trim Switch

A mechanical lever that allows you to adjust the tilt angle of the outboard motor in the water. This adjustment is crucial for optimizing the efficiency of the engine’s thrust based on the design of the boat or tender hull.

 Pilot Water Hole

Outboard motors are typically cooled by continuously circulating water around the engine block and head. Unlike a car’s sealed system, outboards use an "open" cooling system, where heated water is expelled back into the body of water. The outlet for this cooling system is referred to as the pilot water hole.

 Flush Plug

Larger outboard motors often have a dedicated opening for flushing the cooling system.

 Oil Drain Plug

This is straightforward: four-stroke outboard motors, which are lubricated with a fuel-oil mixture, require oil for proper lubrication. Just like in vehicles, this oil must be changed periodically, necessitating an oil drain plug.

 Clamp Bracket

A large U-shaped bracket, typically with two sides, used to secure the outboard motor to the transom or rear of the boat. It usually features a small pin that can be inserted into various holes to fine-tune the motor's angle relative to the water.

 Anodes

Anodes come in various forms and are often missing from smaller or older motors. Essentially, an anode is a piece of metal that provides a path of least resistance for electrical currents exiting the motor. Known as "sacrificial" anodes, they gradually wear out over time and are generally replaced every few years. They are made from different metals with varying strengths.

 Anti-Cavitation Plate

Cavitation occurs when the propeller’s thrust lowers water pressure around it, allowing air to be drawn in. This phenomenon can reduce the motor’s efficiency and performance. To combat this, manufacturers install a metal plate above the propeller to minimize cavitation effects.

 Trim Tab

Although not a serviceable component, the trim tab is a molding located on the back of the anti-cavitation plate that enhances steering control.

 Gearcase Oil Level Plug

All outboard motors have a gear mechanism at the bottom of the drive shaft that transfers power at a 90-degree angle to the propeller shaft. This gear is housed within the gearcase (the bulbous section just behind the propeller) and is lubricated with a specific type of high-temperature gear oil. The oil level is monitored and replenished through the gearcase oil level plug, with the oil generally needing to be level with this opening.

 Gear Oil Drain Plug

This plug serves as the exit point for gear oil when it’s time for a change. Like most lubricants, gear oil should be replaced according to the manufacturer’s recommendations, typically based on usage hours or time intervals.

 Water Intake Hole

A small opening in the lower unit casing that allows fresh (or salt) water to enter the cooling jacket. This hole may also have a fine mesh filter to prevent dirt and plant material from entering the system.