How to Mount an Outboard Motor

While inboard motors are mounted inside the midsection or front of the boat transom, outboard motors are mounted onto the outside of the transom. These motors are designed for easy installation, and the position allows more room in the boat's interior. Beyond a fairly straightforward installation, outboard motors offer an impressive horsepower-to-weight ratio. These motors are available in two engine variations — two- or four-stroke engines.

While installation is relatively simple, it's essential to perform each mounting step correctly. If the motor is mounted incorrectly, you may experience less power or excessive drag. Incorrect mounting can also cause low RPMs and make it harder to control the boat.

In this handy guide, we'll discuss how to mount an outboard motor, explain testing techniques and provide valuable motor maintenance and storage advice to ensure your boating hobby is a straightforward and rewarding journey.

Understanding Mounting Basics

Before you can dive into the mounting process, it's essential to understand the different parts of the outboard motor. You'll also need to gather a few tools and supplies to get started.

Identifying Essential Boat and Motor Parts

Outboard motors have three primary part sections — the powerhead, a midsection and a lower unit. The powerhead encases the engine, fuel tank and carburetor. It also includes reed valves and a pull cord to start the engine. This section does not enter the water and is positioned above the transom for ease of use.

The midsection of the outboard motor contains the exhaust housing and the mounting system. The mounting system includes brackets, bolts and a transom pad. This system secures the motor to the transom or the back of the boat.

The lower unit contains the propeller that powers the boat through the water and a skeg below the propeller. This section is positioned below the water level.

Selecting the Right Tools and Supplies for Installation

To secure the outboard motor to the transom, you will need to gather the following tools and supplies:

• Drill
• A torque wrench
• Mounting boards
• Nuts and washers
• Marine adhesive sealant
• Mounting bolts or long studs

To find the right tool and supply sizes, refer to the manufacturer's manual. The manual provides detailed guidelines for all the essential tools in relevant sizes. In some cases, the manufacturer may include some of these items as accessories.

Depending on the size and weight of your outboard motor, you may need a lifting device like a crane or a hoist. However, if you want to mount a portable or small outboard motor, a lifting device may not be necessary.

Step-by-Step Guide to Secure an Outboard Motor

When fitting the outboard motor, the inside of the mounting bracket must be in line with the top level of the boat. The bottom of the midsection will then be level with the water line, and the lower unit will be level with the lowest point of the boat, allowing the propeller to work beneath the water. These guidelines are relevant when using a motor with a cavitation plate that can line up with the lowest point of the boat.

For portable motors and small outboard motors like the Tohatsu 30 horsepower outboard motor, you can attach the motor to fixed mounting pads or directly onto the transom. Once you have found the correct position, mark the position of the transom mount to secure the two mounting boards. Then, use a drill to attach one mounting board on the inside of the transom and the other board on the outside of the transom. Secure the boards with mounting bolts and place washers and nuts on either end of the bolts. These mounting pads will provide support for the motor and protect the transom from damage.

Next, lift the outboard motor into position again and secure the mounting brackets on the transom, using the mounting boards to find the correct position. These brackets will fit around the top of the transom, securing on the inside. You can use a torque wrench to tighten the bolts in the bracket. With portable motors, you can fasten the screws on the mounting brackets by hand to secure the motor.

With larger outboard motor designs like the Tohatsu 75 horsepower outboard motor, you must drill bolt holes before securing the bracket to the bolts. Use a lifting device to lift and level the motor into position. Then, apply a marine adhesive sealant to the bracket around the bolt holes. Move the motor to line the bracket up to the bolts in the transom and secure the bolts with a torque wrench.

Now that the outboard motor is fixed to the transom, you can connect the electrical and fluid lines.

Prioritizing Safety During Installation

When mounting any kind of outboard motor, the primary safety concern is lifting and positioning the motor. While large motors can weigh over 390 pounds, even smaller motors weighing about 120 pounds can be heavy to lift and mount correctly.

When mounting a large motor, use a lifting device to ensure the motor can be positioned accurately. A lifting device can prevent accidents that could lead to personal injury or damage to the engine. Even lighter motors weighing over 100 pounds should be lifted with a device. The device ensures a steady lift and accurate positioning.

Smaller portable motors only weigh about 40 pounds and don't require a lifting device. These motors are light enough to lift and position manually.

Aligning and Installing the Engine Correctly

While correct lifting techniques are essential to avoid injury and accidental damage to the motor, perfect alignment is also crucial to ensure the engine can power the boat. 

Guidelines for Proper Outboard Motor Mounting

If the motor is positioned too high, an unleveled plane can cause the prop to blow out. The boat will also have less drag as contact with the water breaks. You won't be able to reach higher speeds if the outboard motor is too high to reach the water. 

Conversely, if the motor is mounted too low, you'll experience low RPMs and excessive drag. These complications make it harder to control the boat and adjust speeds. You may also notice extreme water sprays. 

To avoid these issues, measure the positioning of each section of the outboard motor relative to the boat. Use a measuring stick to ensure the lower unit's cavitation plate accurately lines up with the bottom of the boat. 

Choosing the Right Bolts for Outboard Mounting

When choosing marine fasteners, the type of bolt and the material are important considerations. Because the bolts are exposed to water, the material must be able to withstand moisture exposure. Otherwise, rust will degrade the integrity of the bolts and you'll need to replace them frequently. 

Stainless steel bolts are a wise investment. Beyond metal type, look for double-nut locking or Nylock nuts to ensure the bolts are fixed in place. It's wise to pair marine-grade sealer with your marine fasteners. Stainless steel is still prone to crevice corrosion, which can cause the length of the bolt to deteriorate while the bolt head and nuts are still in good condition. 

Apply the sealant to the bolts before driving them through the transom. The extra step will protect the bolts from water and crevice corrosion. 

Conducting Water Testing and Making Adjustments

You need access to water to test your outboard motor in water. However, you don't have to head to the ocean — you can test the motor at home with a large bucket of water. Testing the motor in water is essential to avoid burning out the water pump.

With the outboard motor mounted to the boat, position a large bucket of water beneath the motor so the propeller on the lower unit is fully submerged. Prime the engine by adding oil and fuel, and then open the vent on the fuel tank. Push the throttle handle forward and use the choke system to modify the air-to-fuel ratio. You'll hear a clicking sound when pressing the choking system.

Then, pull the cord to start the engine. The motor should spew water from the water pump outlet and run with stable revs. 

Next, you can take your boat onto the water to check the mounting position. You'll need to spend some time navigating the waters to be sure the mounting position is correct. If you notice the signs of an incorrect mounting position, you'll need to remount the outboard motor to either increase or lower the motor height.

Maintaining Your Outboard Motor

Whether you have a small portable outboard motor or a large one, routine maintenance is essential to keeping the engine in good condition. 

Routine Maintenance for Longevity

Most manufacturers recommend changing the oil and oil filter and running through a basic maintenance checklist after 100 hours on the water. However, if you spend less time on the water, performing engine maintenance at least once a year is important. If you run your boat in dirty water environments or trolling for long periods, performing maintenance more frequently is best. 

Here is a breakdown of basic engine maintenance tasks for an outboard motor:

• Replace the fuel filter.
• Lubricate the moving parts.
• Inspect the propeller for damage.
• Inspect the fuel lines and fuel tank.
• Change the engine oil and replace the oil filter.
• Test the battery with a voltmeter or multimeter.
• Inspect the steering and throttle or choke system.
• Inspect the engine system to find loose or damaged wires.

While you don't need to be an expert mechanic to conduct basic outboard motor maintenance, you can reach out to a maintenance service. Fawcett Boat Supplies offers outboard maintenance and repair services. We stock quality engine parts to replace any damaged components. Whether your outboard motor needs part repair or replacement, we have the skills, tools and quality parts to restore your motor to top condition. 

Effective Storage Solutions

While engine maintenance is essential, storing the motor correctly is just as important. Proper storage becomes even more crucial when the motor is unused for over a month. In this case, the standing fuel can cause problems. 

Store the motor in an upright position, preferably mounted to the boat. Use a cover to prevent dust and debris from gathering on it, and keep it in dry conditions. 

Flush and drain the cooling system. You'll need to attach a garden hose to the flush adapter and then tilt the motor up to flush all the water out of the cooling system while the engine idles for about five minutes. If you run the motor in saltwater, it's wise to flush the cooling system with fresh water after every use. 

When the engine is out of use for extended periods, add a fuel stabilizer to the fuel tank and run the engine for about 10 minutes. However, if the motor will be out of use for longer than 60 days, it's best to drain the fuel from the tank before storage. 

Troubleshooting Common Outboard Motor Issues

Even when following all the mounting steps closely, common issues can arise. Here are some practical solutions to consider:

• The motor won't turn on: Disconnect and remove the battery. Disconnect the black cable first before removing the red cable. Then, inspect the battery for damage and replace it if you notice signs of corrosion or leaking. If there are no signs of damage, test the battery with a voltmeter or multimeter. 
• The engine surges and shuts off: Check the fuel lines for kinks or damage. Clear the fuel lines to remove any blockages, and try to start the engine again. Next, check the fuel filter and replace it if it is dirty or damaged.
• The propeller is vibrating too much: If damaged, it will vibrate excessively, increasing fuel consumption. Check the propeller for visible damage and replace the part if you notice dents or bends. 
• Incorrect trimming: The outboard motor trim position can impact performance. If the trim is positioned out, the propeller will push down into the water, and the nose of the boat will pull up. In contrast, if the trim is positioned down, the nose of the boat will also push down. Adjust the trim position to keep the boat level on the water.
• Incorrect motor size: The outboard motor's horsepower and weight should complement your boat. A good rule of thumb is to have one horsepower for every 20-40 pounds of boat weight. 

When to Seek Professional Help

Suppose you have followed the correct mounting steps and performed basic troubleshooting, and the outboard motor is not running smoothly or does not power your boat sufficiently. In that case, it's best to reach out for professional help.

Fawcett Boat Supplies can help identify the issue and perform relevant maintenance, repairs or part replacements. Our mechanics can diagnose and restore your outboard motor. In some cases, we may recommend a new motor when major repairs exceed the costs of a replacement. 

Choose Fawcett Boat Supplies for Your Boating Needs

Fawcett Boat Supplies is a family-owned business located in Maryland. We've provided the boating community with expert services and quality boating products since 1948. Because we have so many decades of experience, you can trust us to provide superior-quality products and services.

We strive to make your boating experience as convenient as possible — whether you're new to the boating community or a seasoned boating expert. Contact us online to learn more about our services, or browse our range of outboard motors to kit your vessel with quality.