The lower unit houses some of the most crucial components of the outboard motor. These include the gearbox, various shafts, and the water pump. A bad or gone unit means your boat won\u2019t propel. Plus, your engine might suffer irreversible damage. <\/p>\n\n\n\n
To prevent the chain of negative events, you must detect the symptoms of a blown lower unit at the earliest. These include an erratic motor, a heated engine, strange noises, etc. Leaks and diminished performance can also be present. <\/p>\n\n\n\n
Now, you might have experienced some of these symptoms in your outboard. But you are still in doubt about whether to blame the lower unit. Learn about them in more detail and confirm your diagnosis. <\/p>\n\n\n\n
The lower unit will start showing signs when it’s blown out or about to be soon. If you are careful enough to detect these symptoms early, you can prevent the faulty unit from affecting other parts of your outboard.<\/p>\n\n\n\n
When the lower unit fails, you will often find that your Outboard motor is locked or reluctant to propel. This behavior of the motor can feel somewhat erratic. <\/p>\n\n\n\n
It usually indicates damage to one of these two contents in your lower unit- shift shaft and prop shaft.<\/p>\n\n\n\n
The shift shafts control two things. It puts your Outboard motor either in or out of gear. The shaft’s relation with the transmission makes this possible. <\/p>\n\n\n\n
It also determines the direction of your propeller\u2019s rotation. So, to properly start and move the boat forward\/backward, the outboard motor needs the shift shaft to be in good health. <\/p>\n\n\n\n
Another reason for the motor to lock up is a faulty prop shaft. The propeller shaft connects to the pinion bearings and gains horizontal rotational power from the gear case. <\/p>\n\n\n\n
As a result, the propeller rotates. When the shaft\u2019s damaged, the propeller will lock up. <\/p>\n\n\n\n
A lower unit failure in the Outboard Motor can readily affect the powerhead. Among them, a heated engine is the most important. However, this can also happen if the engine is very old. <\/p>\n\n\n\n
An engine heating up frequently from lower unit failure can stop working soon. The heated engine will also damage other parts of the powerhead. Such as the pistons and cylinders. <\/p>\n\n\n\n
The reason for this is the water pump in the lower unit. This pump propels up water throughout the engine to keep it cool. <\/p>\n\n\n\n
If damaged impeller blades are inside the pump, it will fail to suck the water outside the boat. <\/p>\n\n\n\n
On different occasions, the fault might be within the drive shaft of the lower unit. <\/p>\n\n\n\n
The driveshaft rotates the impeller blades and helps the motor draw water in the first place. So, if the drive shaft has worn out, the pump would fail to keep the engine cool. <\/p>\n\n\n\n
If oil or similar fluids are dripping from your outboard motor, you most likely have a blown lower unit.<\/p>\n\n\n\n
All the shafts and the gearbox use oil and lubricants for smooth movement. Various seals and gaskets keep these oils confined to where they are needed. However, sometimes these seals can break and cause leakage. <\/p>\n\n\n\n
There are three seals and two gaskets in the lower unit. These are the driveshaft, prop shaft, and shift shaft oil seals. And the O-rings of the shift shaft plate and gearbox bearing housing. <\/p>\n\n\n\n
Among them, the prop shaft oil seal is the most exposed. So, it is the commonest seal to damage. This is the first seal you should check when you have a leaky outboard.<\/p>\n\n\n\n
Unlike the prop shaft oil seal, the other seals and gaskets are mostly out of sight. <\/p>\n\n\n\n
However, if you notice a grey sludge in your outboard during a lube change, you can correctly assume that the O-ring in the gearbox has broken. Because this sludge appears when water and gear lube mix together. <\/p>\n\n\n\n
Your outboard might be losing power, despite a good source and engine. You can consider a failing lower unit in that case. Most probably, the gearbox has blown out. <\/p>\n\n\n\n
The drive shaft brings vertical rotational power from the engine to the gearbox. The gears (forward, reverse, pinion) and the dog clutch translate it into horizontal prop shaft rotation.<\/p>\n\n\n\n
Over time, the gear shims wear out. As a result, the exchange between the drive and prop shaft becomes weak. To the driver, it feels like the outboard is losing power. <\/p>\n\n\n\n
A bad gearbox can also be variably noisy. Sometimes you might hear a clunking in your outboard. It indicates some part has fallen off the motor assembly. <\/p>\n\n\n\n
In most cases, it\u2019s the tooth of some old gear. The piece can easily stick between the working gears and bring your whole outboard to a stop. <\/p>\n\n\n\n
Another symptom is hearing the outboard grinding. The noise comes during gear changes. In this case, the dog clutch probably has worn-out teeth. <\/p>\n\n\n\n
The clutch is the connection between the shift and prop shaft. The shift engages the clutch with Forward and Reverse gears. In turn, the propeller changes its direction. <\/p>\n\n\n\n
Changing gears at high RPM causes the dog clutch to wear out quickly. Another cause is correct rigging. <\/p>\n\n\n\n
The engine will get the wrong input if the outboard’s cable connections are bad. This will put the drive and prop shaft out of sync and stress the dog clutch. <\/p>\n\n\n\n
Apart from these, your gearbox will constantly make a chattering noise. It indicates the gears are old and loose.<\/p>\n\n\n\n
The lower unit has your boat’s propeller. So, a damaged lower unit means your boat isn\u2019t moving. <\/p>\n\n\n\n
However, if you are aware of the reasons behind the unit\u2019s failure, you might be able to prevent the situation. Let\u2019s have a look- <\/p>\n\n\n\n
A failing lower unit doesn\u2019t always mean you have to buy a new outboard. You can replace the failing parts and rebuild your lower unit. <\/p>\n\n\n\n
If you do it correctly, your outboard will again run properly and may last its normal course. Let\u2019s have a look at the associated costs. <\/p>\n\n\n\n