Yamaha Lower Units - Guide to Care & Maintenance

Keep Your Yamaha Outboard Running at Max Power

The lower unit of a Yamaha outboard motor is a critical component that transfers power from the engine to the propeller. It contains a variety of gears, bearings, and seals that are essential for proper operation and can be damaged by exposure to saltwater, debris, or other hazards. Routine maintenance and occasional repairs are necessary to keep the lower unit in top condition and prevent costly damage or failure.

If it’s your first time owning a Yamaha outboard motor or you’re a seasoned expert, getting familiar with the lower unit is important. If you’re hearing about it, we’ve got you covered. Yamaha Online Parts understands the importance of keeping your engine functioning and performing for years to come.

We’ll cover the following topics in detail:

The Basics of Yamaha Lower Units
What Type of Maintenance is Required for Yamaha Lower Maintenance?
Service Intervals for Yamaha Lower Units
Which types of OEM Yamaha lower unit oil should I use?
Yamaha Lower Unit Schematics
Why Should I Only Use OEM Yamaha Lower Unit Parts and Products?
Learn More with Yamaha Online Parts
Yamaha Outboard Lower Unit Maintenance FAQ
Purchase OEM Yamaha Lower Unit Parts with Yamaha Online Parts

The Basics of Yamaha Lower Units

So, what is the lower unit on a boat?

The lower unit is responsible for converting your outboard engine's power to the prop shaft's rotation. The prop shaft is what moves the propeller, which is what moves your boat.

As you can see, all these moving parts are connected. You’re not going to get very far without them! Fortunately, all you need to do is keep up with simple routine maintenance to keep your Yamaha lower unit in pristine condition.

List of Yamaha Lower Unit Parts

The parts of an outboard motor lower unit typically consist of several parts, including:

Gearcase: The main body of the lower unit that houses the gears and bearings.
Gear set: The set of gears that transmit power from the driveshaft to the propeller shaft.
Propeller shaft: The shaft that transfers power from the gears to the propeller.
Water pump: The part responsible for circulating water through the engine to prevent overheating.
Anode: A sacrificial metal component designed to corrode instead of other metal parts in the engine.
Seals and gaskets: These components prevent water from entering the engine and oil from leaking.
Housing: The protective casing that surrounds the lower unit components.
Shift rod: The component that connects the shift lever to the gearcase, allowing the operator to change gears.
Oil drain plug: A plug located on the bottom of the lower unit that allows for easy oil changes.

What Type of Maintenance is Required for Yamaha Lower Maintenance?

Maintenance for Yamaha outboard lower units typically involves the following tasks:

Lubrication: Regular lubrication of the lower unit gearcase with high-quality Yamalube lower unit oil can help to protect against wear and corrosion and ensure smooth operation.
Inspection: Regular inspection of the lower unit for leaks, cracks, and damage can help to detect and address any issues before they become major problems.
Anodes: Installing and regularly inspecting anodes on your lower unit can help to protect against galvanic corrosion.
Water Pump Impeller: Replacing the water pump impeller annually can help to ensure proper cooling and prevent overheating.
Seal and O-rings: Regular inspection and replacement of seals and o-rings can help to prevent leaks and maintain the integrity of the lower unit.

It’s important to understand that Yamaha lower unit maintenance requires not only the tasks above but also a set of other maintenance tasks to ensure the engine as a whole performs well.

By following these Yamaha lower unit care and maintenance guidelines, you can help protect your lower unit and ensure its longevity and performance. Be sure to consult your Yamaha owner's manual and dealer for specific maintenance requirements and recommendations for your outboard.

Service Intervals for Yamaha Lower Units

Yamaha outboard maintenance is usually broken up into regularly-occurring service intervals based on your usage. These include:

Initial Break-in Period
After Each Use
20-Hour Service
100-Hour Service / Annual Maintenance
Winterization
Season Breakout

Initial Break-In Period

Breaking in a Yamaha outboard motor is an important step in ensuring your motor's long-term performance and durability. The break-in process helps to prevent excessive wear and damage to the lower unit, which can be caused by running the engine at high speeds and under heavy loads before the components are properly seated and lubricated.

How to Break-In Your Yamaha Engine & Lower Unit

The break-in process involves gradually increasing the engine's speed and load over the first few hours of operation. Here are the general steps to break in a Yamaha outboard motor:

Start the motor and run it at idle speed for several minutes, allowing the engine to warm up.
Slowly increase the speed to 2/3 of the maximum rated RPM for the first hour of operation.
Gradually increase the speed to 3/4 of the maximum rated RPM for the next two hours.
For the remaining hours of the break-in period, gradually increase the speed to the maximum rated RPM and frequently vary the speed and load on the engine.

During the break-in period, it's important to avoid operating the engine at full throttle or under heavy loads, as this can put excessive wear on the engine components and the lower unit. The goal is to allow the engine to wear in gradually and properly seat the piston rings and other components.

Note: If purchasing a refurbished lower unit or engine, follow the steps above to break in the outboard. Some refurbishers handle this process to avoid potential customer issues (especially if the parts are under a new warranty); boaters may have to perform this task themselves or have their engine serviced by a marine mechanic.

After Each Use

Performing maintenance on your Yamaha outboard lower unit after each use is an important step in keeping your motor running smoothly and preventing damage from saltwater corrosion. Here are some maintenance tasks you should perform immediately after each use:

Rinse with fresh water: Rinse the entire lower unit and other metal components, such as the propeller and steering components, with fresh water. This will help remove any salt, sand, or other debris that may have accumulated during use.
Inspect for damage: Check the lower unit for any signs of damage, such as cracks or dents. If you notice any damage, address it promptly to prevent further damage and potential safety hazards.
Check the propeller: Inspect the propeller for any signs of damage or wear, such as dings or chips. If you notice any issues, have the propeller repaired or replaced as necessary.
Check the anodes: Inspect the anodes (also known as sacrificial zincs) for signs of wear or corrosion. If the anodes are more than 50% depleted, they should be replaced to ensure continued protection against corrosion.
Lubricate moving parts: Lubricate moving parts, such as the propeller shaft, with marine-grade lubricant. This will help protect against corrosion and reduce wear.
Drain the lower unit: Drain any water that may have entered the lower unit during use. This is particularly important if you operate your boat in saltwater.
Apply anti-corrosion products: Apply an anti-corrosion product, such as Yamashield Rust & Corrosion Protectant, to the lower unit and other metal components. This will help protect against saltwater corrosion.

By performing these maintenance tasks immediately after each use, you can help keep your Yamaha outboard lower unit in good condition and extend the life of your motor. Refer to your owner's manual for specific maintenance recommendations, and consult with a qualified marine mechanic if you have any questions or concerns.

20-Hour Service

A 20-hour service interval for a Yamaha outboard motor typically involves a combination of inspections, lubrication, and replacement of specific components as needed, to ensure that the motor is running smoothly and reliably.

The specific maintenance tasks involved in a 20-hour service interval for a Yamaha outboard motor may vary slightly depending on the particular model and year of the motor but generally include the following:

Changing the engine oil: At the 20-hour mark, it's recommended to change the engine oil and oil filter to ensure that the engine is properly lubricated.
Inspecting the propeller: Check the propeller for any signs of damage or wear, and make sure it is tightened securely on the propeller shaft.
Inspecting the fuel system: Check the fuel hoses, connections, and filters for any signs of damage or wear, and make sure they are properly tightened.
Checking the water pump: Inspect the water pump impeller for any signs of wear or damage, and replace it if necessary. Check the water pump housing and inlet screens for any debris or damage, and make sure they are clear and functioning properly.
Inspecting the electrical system: Check the battery, wiring, and connections for any signs of damage or corrosion, and make sure they are clean and properly secured.
Lubricating moving parts: Lubricate any moving parts, such as throttle and shift linkages, steering components, and other key parts, as needed.
Checking and adjusting the idle speed: Check and adjust the idle speed as needed to ensure smooth operation.

100-Hour Service / Annual Maintenance

Similar to the 20-hour service with a few additional tasks, the maintenance tasks involved in a 100-hour service interval (or annual maintenance) for a Yamaha outboard motor may vary depending on the specific model and year of the motor but generally include the following:

Replace gear lube: Depending on your usage, the Yamaha lower unit gear oil should be extracted and changed at the 100-hour or one-year mark, whichever comes first.
Changing the engine oil and filter: The engine oil and filter should be changed at least every 100 hours of operation or once per year, whichever comes first.
Replacing the fuel filter: Replace the fuel filter to ensure that the fuel system is free of debris and functioning properly.
Inspecting the spark plugs: Check the spark plugs for signs of wear or fouling, and replace them if necessary.
Checking the battery: Inspect the battery and terminals for any signs of damage or corrosion, and make sure they are clean and properly secured.
Inspecting the cooling system: Check the cooling system for any signs of damage or wear, and make sure the thermostat is functioning correctly.
Inspecting the propeller: Check the propeller for any signs of damage or wear, and make sure it is tightened securely on the propeller shaft.
Inspecting the steering system: Check the steering system for any signs of damage or wear, and make sure it is functioning properly.
Checking the timing belt: If your motor has a timing belt, inspect it for signs of wear or cracking, and replace it if necessary.
Lubricating moving parts: Lubricate any moving parts, such as throttle and shift linkages, steering components, and other key parts, as needed.

Winterizing Your Yamaha Outboard Lower Unit

Winterizing your Yamaha outboard lower unit is an important step in preparing your boat for the colder months and protecting it from the effects of freezing temperatures and moisture.

Here are some of the key steps involved in winterizing your Yamaha outboard lower unit:

Change the gear oil

Start by draining the gear oil from the lower unit and replacing it with fresh, high-quality gear oil suitable for use in cold temperatures. This helps to prevent moisture buildup and corrosion inside the lower unit.

Check the seals

Inspect the seals on the lower unit to ensure they are in good condition and not cracked or damaged. Replace any seals that show signs of wear or damage to prevent water from entering the lower unit.

Grease the bearings

Use marine-grade grease (Yamalube Multi-Purpose Marine Grease Lubricant) to lubricate the bearings inside the lower unit. This helps to protect them from moisture and prevent rust and corrosion.

Flush the lower unit

Use a flushing attachment to flush the lower unit with fresh water and remove any salt, dirt, or other debris that may have accumulated. This helps to prevent corrosion and other damage.

Store the boat properly

Finally, store your boat in a dry, sheltered area for the winter months. Cover the boat to protect it from the elements and prevent moisture buildup.

Season Breakout

To properly prepare your Yamaha outboard motor for hours of reliable use, you should follow these steps for a season break out:

Flush the engine with fresh water to remove salt or dirt accumulated in the cooling system.
Change the engine oil and filter to remove any contaminants accumulated over the season.
Drain and refill the lower unit oil to remove any water or contaminants that may have accumulated.
Inspect the lower unit for any signs of damage, wear, or leaks. Repair any issues found before storing the motor.
Grease the propeller shaft and threads, and the propeller shaft splines.
Remove the propeller and check for any damage or debris that may have become lodged in the propeller hub.
Apply a thin coat of waterproof grease to the propeller shaft and splines to prevent corrosion.
Check and adjust the tension on the drive belts.
Clean the exterior of the motor, including the lower unit, with soap and water, and dry it completely.
Coat any exposed metal surfaces with a corrosion inhibitor.
Remove the battery from the boat and store it in a cool, dry place, or use a battery maintainer to keep the battery charged during storage.

Cover the motor and the boat with a waterproof cover to keep it clean and dry during storage.

Which types of OEM Yamaha lower unit oil should I use?

Yamaha recommends using their Yamalube® brand of lower unit oils in their outboard motors, as they are specially formulated to meet the unique requirements of their lower unit systems. When selecting the appropriate Yamalube® lower unit oil for your Yamaha outboard motor, you should consider the following:

Type of motor: Different types of outboard motors may require different types of Yamaha outboard lower unit oil. Consult your owner's manual or a qualified Yamaha dealer to determine the appropriate type of oil for your motor.
Operating conditions: If you operate your Yamaha outboard motor in extreme conditions such as high speeds, heavy loads, or high temperatures, you may need to use a higher-performance oil such as Yamalube® Gearcase Lube (SAE90) or Yamalube® Gearcase Lube HD (SAE 80 W-90).
Oil viscosity: Lower unit oils come in different viscosity grades, as indicated by their SAE (Society of Automotive Engineers) rating. Consult your owner's manual or a qualified Yamaha dealer to determine the appropriate viscosity grade for your motor.
Oil quantity: The lower unit oil required for your Yamaha outboard motor will depend on its specific model and year. Consult your owner's manual or a qualified Yamaha dealer to determine the appropriate quantity of oil for your motor.

Using only OEM Yamaha lower unit oil in your outboard motor is important to ensure proper lubrication and protection of your lower unit components. Using non-approved oils or additives may void your Yamaha warranty or cause damage to your motor.

Yamaha Lower Unit Schematics

Yamaha Lower Unit Schematics are an important tool for anyone who owns or works on Yamaha outboard motors and can help ensure that the motor runs smoothly and reliably.

What are Yamaha Lower Unit Schematics?

Yamaha lower unit schematics are diagrams that illustrate the various components and parts of the lower unit of a Yamaha outboard motor. This includes the gearcase, driveshaft, propeller shaft, water pump, and other key parts that are involved in transferring power from the engine to the propeller and, ultimately, to the water.

Why Do I Need Yamaha Schematics?

These schematics are typically used by mechanics and boat owners to understand better how the lower unit of the outboard motor works and to diagnose and troubleshoot any issues that may arise. By using the Yamaha lower unit diagram, a technician or DIY boater can identify specific parts and components that may be causing problems and then work to repair or replace them as necessary.

In addition, Yamaha lower unit schematics can also be useful for ordering replacement parts or upgrades for the motor. By referencing the schematic, a boat owner can ensure that they order the correct part for their specific model and year of outboard motor.

Note: While many boaters may have their owner’s manual on hand as a reference for making repairs or may refer to online videos as a guide, engine schematics are essential if you plan on performing maintenance tasks throughout your Yamaha outboard’s lifetime.

It should also be noted that it’s not uncommon to find misinformation online, especially if a particular model of Yamaha outboard featured in a video doesn’t contain specifics (i.e., which year the engine was manufactured, Yamaha 115 lower unit versus Yamaha 150 lower unit, etc.). By using an engine schematic, you can cross-reference any info to ensure you’re ordering the right parts and making the right repairs.

Yamaha Lower Unit Schematics Online

To ensure that you have a handy reference to perform repairs AND order the exact parts you need for your lower unit, you’ll need Yamaha Outboard Gauge Schematics. Refer to this online Yamaha Engine Schematic database (powered by Snap-On Electronics Parts Catalog / Snap-On EPC) to help you find the right parts number and order on Yamaha Online Parts.

Once you’ve navigated to the database, you’ll only have to make a few clicks to match your particular model of outboard and needs:

Start by clicking on the matching model number and horsepower of your engine
The next screen will offer more specific models
Once you’ve matched your outboard’s year, you’ll have several options regarding your specific engine model. Select your engine from the available options.
In the next screen, you’ll be presented with a list of schematics labeled by the engine system or part type. Click on the appropriate schematic.
- Note: Due to the specificity of each schematic, you may need to click on several schematics until you’ve found the exact part.
Once you’ve selected the schematic, you’ll have a visual reference indicating all of the gauge’s parts and components with numbers corresponding to the part number. These schematics can be printed or emailed to you as a reference.
Click the matching part on the schematic OR click the corresponding number on the parts list (which will highlight the parts on the schematic for verification).
Next to each list of each part is a shopping cart icon. Clicking the icon will add the part to a Shopping Cart list at the bottom of the screen (on desktop computers). Continue this process to populate the list with everything you need.
The Shopping List organizes each part by the following categories:
1. OEM
2. Model
3. Part Number
4. Qty (Quantity)
5. Description
6. Cover
7. Retail (Pricing)
On the left side of the list, you’ll find three icons:
1. Clear Shopping Cart
2. Print Shopping Cart
3. Email Shopping Cart

Once you’ve printed or emailed your completed list of parts, enter the Part Number into Yamaha Online Parts’ Search box, add the matching item(s) to your shopping cart, and finalize your purchase.

Why Should I Only Use OEM Yamaha Lower Unit Parts and Products?

When replacing parts in the lower unit, using Yamaha OEM parts is essential. OEM parts are designed for use in Yamaha outboard lower units, ensuring the highest level of quality and compatibility with your motor. Non-OEM or aftermarket parts may not fit properly, be made of lower-quality materials, or fail to meet the standards for performance and reliability.

At Yamaha, the importance of using OEM parts is underscored by their commitment to precision engineering and rigorous quality control standards. Yamaha OEM parts are manufactured to the same exacting standards as the original parts that came with your outboard motor, ensuring optimal performance and longevity. Whether you need to replace a damaged lower unit or simply perform routine maintenance, choosing Yamaha OEM parts is the best way to ensure the safety and reliability of your boating setup.

Learn More with Yamaha Online Parts

Yamaha Online Parts offers plenty of resources for DIY boaters to install, replace, and repair their outboard motor with Yamaha OEM Parts. Search our blog, or start with the following to learn more about everything you need to know about your Yamaha outboard:

Yamaha Outboard Lower Unit Maintenance FAQ

What are the pros and cons of using remanufactured Yamaha lower units?

PROS:

Cost savings: Remanufactured lower units are generally less expensive than brand-new units. This can be a significant advantage for replacing a damaged lower unit without breaking the bank.
Warranty: Many remanufactured lower units come with a warranty that can provide added peace of mind. This warranty may cover the cost of repairs or replacement if there are any issues with the unit.
Environmentally friendly: Remanufactured lower units are a form of recycling that can help reduce waste and promote environmental sustainability.
Availability: Newer lower units tend to be in high demand, so choosing a refurbished lower unit gives you more options.

CONS:

Quality: The quality of a remanufactured lower unit can vary depending on the remanufacturing process and the supplier. There is a risk of receiving a lower unit that has yet to be properly remanufactured or inspected, leading to additional problems or failures.
Compatibility: Remanufactured lower units may not be compatible with all Yamaha outboard models. It's important to ensure that the remanufactured unit is designed to work with your specific outboard motor to avoid compatibility issues.
Longevity: While remanufactured Yamaha lower units can be cost-effective in the short term, they may last less time than a brand-new unit. This can result in additional repairs or replacements in the future.

Overall, using a remanufactured Yamaha lower unit can be a viable option for some boat owners, but it's important to carefully consider the pros and cons before deciding. Choosing a reputable supplier and carefully inspecting the unit before installation is important to ensure that it meets the necessary quality and compatibility standards.

Which Yamaha lower unit maintenance tasks should only be performed by qualified marine mechanics?

While Yamaha outboards are built to be maintained by DIY boaters, several Yamaha lower unit maintenance tasks may be best left to a qualified marine mechanic if you don’t have the free time or proper tools. These include:

Adjusting the shift linkage: Adjusting the shift linkage can be critical to ensure smooth shifting and prevent damage to the gears and bearings in the lower unit. It's important that this task is done correctly to avoid potentially costly repairs. Therefore, it is recommended that a qualified marine mechanic performs this task.
Inspecting gears and bearings: Inspecting the gears and bearings in the lower unit requires specialized knowledge and tools and should only be performed by a qualified marine mechanic.
Adjusting gear lash and backlash: Adjusting the gear lash and backlash in the lower unit is a delicate procedure that requires precise measurements and specialized knowledge. Improper adjustment can result in severe damage to the lower unit and should only be performed by a qualified marine mechanic.
Installing a new propeller shaft or gear set: Installing a new propeller shaft or gear set in the lower unit requires specialized knowledge and tools to ensure proper alignment and fit. This should only be performed by a qualified marine mechanic.

Lower unit maintenance can be complex and requires specialized tools and knowledge. Therefore, it's important to have these tasks performed by a qualified marine mechanic with the necessary experience and training to ensure your Yamaha outboard motor is properly maintained and operating smoothly.

How long does it take to perform a Yamaha lower unit replacement?

The time it takes to perform a Yamaha lower unit replacement can vary depending on the experience of the person performing the replacement, the complexity of the repair, and the tools and equipment available. Generally, a lower unit replacement can take a few hours to a full day.

Some of the factors that can affect the time it takes to perform a Yamaha lower unit replacement include:

Access to the outboard motor: If the motor is difficult to access, it may take longer to complete the replacement.
Type of outboard motor: The type of motor and its configuration can also affect how long the replacement takes.
Complexity of the repair: Some lower unit replacements may be more complex than others, requiring more time and skill.
Parts availability: If parts need to be ordered, it may take additional time to complete the repair.

Following the manufacturer's guidelines for replacing the lower unit and using the proper tools and equipment to ensure a safe and successful repair is essential. If you're not experienced with outboard motor repair, it's recommended to have a professional mechanic perform the replacement.

Purchase OEM Yamaha Lower Unit Parts with Yamaha Online Parts

In conclusion, proper care and maintenance of the lower unit in a Yamaha outboard motor are crucial to ensure optimal performance and longevity. The lower unit is a complex component that requires routine maintenance with Yamaha OEM parts to ensure quality and compatibility with your motor and give you peace of mind when out on the water.

Yamaha Online Parts has what you need. We carry a full catalog of Yamaha outboard lower unit parts and have what you need to fit any engine model. We also offer international shipping to select countries.

Proper Yamaha outboard engine maintenance requires Genuine OEM Yamaha parts. Trust the experts at Yamaha Online Parts for all your outboard engine needs.