yamaha outboard lower unit problems

Yamaha Outboard Lower Unit Problems- Reasons Explained!


On outboard-powered vessels, it’s critical to keep debris off the prop while also performing other essential maintenance. Otherwise, you risk getting a faulty outboard lower unit.

So are you facing Yamaha outboard lower unit problems?

Shifting problems may result from defective outboard lower components. Other signs include magnetic particles on the outflow screw magnet. It can also show clunking sounds when shifting. It may even show the inability to shift into gears. After identifying the problem you can solve them.

This article will give us more information on it.

What Is an Outboard Motor’s Lower Unit?

The lower unit’s bottom section is in charge of modifying the propeller’s lined with an industrial swivel.You must maintain the lower unit to keep your outboard running smoothly and for as long as possible.

Simple lower unit maintenance measures include routine oil changes and keeping trash. 

How Does a Lower Unit Function?

The gearcase is another name for the lower component. It is part of the outboard motor. This is the powerhead of the engine. It is attached in order to transmit rotation and power to the propeller.

Your boat can propel itself forward or reverse through the water because the propeller revolves.

If a component of the lower unit malfunctions or fails, you may become stranded in the water. 

How Can I Tell If My Outboard Lower Unit Is Faulty?

A faulty outboard lower unit can cause a variety of problems, but the hereunder are the most frequent issues. Let’s look at them.

Water in Gear Case Lubricant

As previously stated, the presence of water in the gearbox lube indicates a problem. When replacing the lubrication, you can search for warning indicators of danger.

Before the water in the gear, the lube causes the lower unit to fail. The switch rod linkage or the linkage designed to connect to the handle enables the operator to manually process and change gears.

This may be to blame if the outboard motor drifts out of gear. Any broken or damaged elements in the upper or lower shift rod linkage, such as the bearing surfaces or coupler, should be supplemented.


It is crucial to replace your gear grease every 100 hours for this reason. By doing so, you can identify the issue and stop the leak.

Metal Contamination in the Gear Case Drain Screw Magnet

Never let the metal particles on your lower magnetic gearbox drain screw magnet exceed 3/4″. Mash any contaminants in your hands while inspecting the magnet.

If it becomes a gray powder, you can fully discard it. Otherwise, you should be concerned if you feel metal during the process. The magnet almost always has a small quantity of metal on it.

It is only when the metal buildup becomes significant that you should be concerned and begin the process of determining what is wrong with the lower unit.


Start by removing the drain plug with a screwdriver. Some outboards may entail an equipment includes, that also decreases the risk of stripping threads.

Because the lower unit cords are magnetic, you may notice some metal shavings that indicate wear. Nothing to be concerned about if you merely see a few, but an excessive number should be.

Clanking Noises

If you begin to hear repeated clanking noises, it can be the gear or axles. When a tooth falls out, it makes this annoying sound. And at the appropriate RPM, it will become lodged between the gears and blow up the lower unit.

When you attempt to operate your outboard in forward or reverse, you hear a few crunching. But the unit engages. While the sound may be coming from your lower unit, the issue may not.

The clutch dog, which is circled in the image above, gets involved to enable the outboard to run forward or reverse. You’ll hear grinding if the engagement isn’t smooth. 

This noise may indicate that you need to modify your throttle cable so that the shift is finished before applying the throttle and increasing RPMs.


You can oil up the engine if there is a sound. Check out the connection and make sure they are in the proper place.

Milky Oil

A milky or whitish tint in the outboard motor lower unit gear oil implies a water leak, that can also cause the engine to stall or fail. A broken propeller seal is frequently the cause of outboard engine lower unit leaks. 


To solve the problem, the controller should substitute the protective layer and flush the oil.

Your oil must not be milky, but rather dark. If it appears milky, it is most likely because of polluted water by a leaking seal or debris. You need to choose the correct oil for your lower unit.

Instead of simply changing the oil, address the underlying issue. Alternatively, water would then proceed to permeate into the oil, causing the gear box to fail.

You can buy a new gear box if you think it’s needed. Here are some recommendations of the gearbox that you can buy.

Product 1
Product 2

Examine the head gasket on the oil plugs as well. It’s better to upgrade them if they’re worn or frayed. If your gasket separates from the plug and remains in the hole, it’s time to switch out the entire plug.

Propeller Slippage

If the lower unit propeller of an outboard engine sustains damage,it can slide down on its hub and cause impeded outboard steering. Specially, which is often induced by hitting or trying to push against a submerged blockage.

Check for damage and replacing either the wheel or the propeller as necessary.


Position the outboard vertically. The propeller should be parallel to the pavement at all times. If the sewage turtles are in the lower unit’s back.

If they are located on this same bottom of the gearcase’s nose. Then, lean the engine or lower unit up so that the drain screw is in the bottom rank on the gear case.

Place cardboard on the ground beneath the motor. Put the oil pan beneath the prop. It also depends on the lower unit compatibility.

Distancing the Lower Unit from the Powerhead

It is critical to re-grease splines when reinstalling a lower unit. If you’re attempting to pull a lower unit, that ship has sailed. 

The best advice is to gently pry apart the lower unit housing from the powerhead. You can pry the metal against the scrapers with a screwdriver after separating it using thin metal scrapers.

This will safeguard the mating surfaces of the powerhead and lower unit.

Lower Unit Rebuild Costs 

You have several options if your outboard lower unit fails. The option to replace the unit or rebuild it is available.

If you are mechanically inclined, rebuilding the lower unit would be far less expensive than purchasing a new one. However, this will take more time from you than simply making a purchase.

You must decide which is preferable in your situation. 

Thus you solve your Yamaha outboard lower unit problems.


Is it possible to run an outboard motor without the lower unit?

Yes, an outboard motor can be run without a lower unit. Use the flush fitting or a piece of hose connected to the water tube with a hose clamp. As previously stated, on an HPDI, a hose can be connected to the water pump tube, allowing the motor to run.

How often should your outboard lower unit’s oil be changed?

You must replace the oil in your outboard lower unit at 100 hours. Most design can also vary and boat companies recommend changing the gearcase oil in your bottom unit every 100 hours or every year (whichever comes first). Fresh oil is essential for safeguarding the highly congested gears in your bottom unit and preventing serious damage.

What is the weight of Yamaha’s lower unit oil?

SAE 80W-90. Special high viscosity, high-pressure additives protect gears in high speed, high load conditions for extended periods of time.


I hope you have learnt all about Yamaha lower unit problems. This article should assist you in troubleshooting your outboard lower unit issues. 

We want to assist you in keeping your boat operating smoothly and efficiently.

That’s all for today!

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top