For any owner of water transport, whether an avid fisherman or a lover of high-speed walks, knowing the engine is not just a theoretical reference, but a vital necessity. Often in the process of operation, when ordering parts or communicating with the masters of the service center, the question arises: what is the name of the bottom of the outboard motor? The answer is far from as it may seem at first glance, because this zone is composed of many critical elements.
The common people often call this knot simply "leg", but technically competent name - lower unit or suspensionThis is where the torque transfers from the engine to the water, allowing the boat to move, and understanding how the bottom is designed will help you avoid costly repairs and properly preserve the equipment for the winter.
In this article, we will take a detailed look at the anatomy of the underwater part, look at the functions of each element and give practical recommendations for their maintenance. anticavitational more important than it seems, and as a state of sludge It affects the life of the entire motor.
General structure: Daydwood and its purpose
The bottom of the outboard motor, which spans from the mount to the transom to the bottom, is technically called a lower unit, a massive casing that has a complex mechanical system hidden inside it, and the main purpose of this unit is to transfer rotation from the engine crankshaft to the propeller, and also to provide control of the direction of the boat through the rotary mechanism.
Structurally, the lower unit is divided into several functional zones: the upper part often contains an exhaust system and fastening elements to the lower unit pipe, the middle is occupied by a propeller shaft and a gearshift mechanism, and the lower part is completed with a gearbox. Tightness This unit is paramount importance, since the ingress of water inside leads to fatal consequences for gears and bearings.
The material most commonly used is aluminum alloy, which is highly corrosive and durable, but even metal is subject to electrochemical corrosion, especially in salt water, so you can always see the outer part of the lower unit. zinc anodeIt is a force that takes on an aggressive environment.
Always check the condition of the zinc anode before each release into the water in a salty environment. If it has dissolved more than half, it must be replaced urgently, or lower unit itself will begin to corrode.
It's important to understand that a lower unit is not just a pipe, but a complex engineering unit that requires regular lubrication and visual inspection, and damage to the outer skin can lead to hydrodynamic disruption and loss of speed.
Reductor: Heart of the lower part of the motor
One of the key elements at the bottom of Daydwood is gearboxThis is where the rotational direction changes and the propeller forces are transmitted, and inside the gear casing, there are gears that provide forward, reverse and neutral position.
The lubricant is lubricated with a special oil that is poured into the body, and the regular replacement of this oil is one of the most important maintenance procedures. If an emulsion appears in the oil (it becomes milky in color), this is a signal that the oil is not a good idea. plumbing or the seals have lost their tightness.
Why does the gearbox change the oil?
The oil in the gearbox doesn't burn or burn like an engine, it's changed to remove the metal shavings (the wear products of the gears) and check for water, and the water gets through the microcracks in the omentums when the motor cools down when a vacuum is created inside.
The gearbox body is streamlined to minimize water resistance, and it has a propeller shaft that relies on bearings, and the quality of these bearings has a direct impact on smoothness and the absence of vibrations when the motor is running at high speeds.
When operating in shallow water or overgrown waters, the gearbox often takes on impacts on underwater obstacles. propeller This is a priority for manufacturers.
Roll propeller and anchorage system
Finishes the torque chain with a propeller, which is the working organ that converts the rotational motion of the shaft into the forward motion of the boat, and the screw is mounted on the tail of the shaft and fixed by a nut, often protected from self-unwrapping by a splint or counternut.
Between the hub of the screw and gears of the gearbox is often installed damper (a rubber sleeve or spring mechanism) Its task is to extinguish the impact loads when a sharp shift of gear or a screw hits a hard object, protecting the gears of the gear from failure.
- 🚤 Diameter and step The propellers are selected depending on the weight of the boat and tasks: for speed, screws with a large pitch are needed, for thrust - with less.
- 🔩 Protective puck prevents the nut from turning and protects the shaft thread from corrosion.
- ⚓ Slice pin (in some models) breaks on impact, maintaining the integrity of the shaft and gearbox.
It is important to remove the screw regularly to clean the shaft from the winding fishing line or algae. Leaf, caught under the oil oil, can break the tightness and lead to water entering the gearbox. WD-40 or similar lubricants to facilitate the removal of sour nuts.
Cooling system and water intake
The bottom of the motor is critical to the cooling system of the engine, and it's here, in the gearbox or just above, that's where the engine is. water-intakeThrough this hole, water is sucked in by the pump and fed up to the engine to remove heat.
The design of the intake often includes a safety net to prevent large debris, sand or algae from entering the system. Clogging of this unit is one of the most common causes of engine overheating. Visual control of the cleanness of the inlet should be a regular habit.
In addition to the main hole, there are control holes at the bottom of the lower unit to check the pump, and if the engine is running from the control, there is no water jet, it is a malfunction signal. impeller or clogging the system.
In winter, it is important to completely remove the remaining water from this system, purging with compressed air or using special antifreeze preservatives helps to avoid rupture of the pipes when freezing.
Control and steering
The bottom of the outboard motor is movable relative to the lower unit tube, which allows you to change the direction of thrust, and this knot is called the rotary mechanism, which provides maneuverability of the boat, transferring force from the hummel or hydraulic steering to the lower unit.
Inside the rotary mechanism are slip or roll bearings that require lubrication. Often, this assembly has gear shift thrusts that connect the control knob to the gearbox, and the luft in these connections leads to fuzzy gears.
| Element | Function | Frequency of verification |
|---|---|---|
| Turning bracket | Motor-trans connection | Every season. |
| Switching thrust | Transfer of the CPT team | Every time I do. |
| Turn bearings | Rotational maintenance | Every 50 hours. |
| Hydraulics (if any) | Strengthening management | Checking the oil level |
Hydraulic systems are often used to facilitate the control of powerful motors, whose cylinders are also attached to the bottom of the lower unit, and the tightness of these systems is critical: leakage of fluid will make control impossible.
Anticavitational plate and hydrodynamics
Above the propeller is a horizontal plate, which is called anticavitationalIt's a continuation of lower unit and it has an important function: it prevents air from sucking into the propeller blades when the boat is moving.
Without this plate, the water would swirl to form a funnel into which air would fall, a phenomenon called cavitation. When cavitation occurs, the propeller starts to work in an air mixture, loses efficiency dramatically, and the engine makes a characteristic roar and can overheat due to the lack of cooling water intake.
☑️ Checking the condition of the lower part
On some motor models, especially those designed for shallow water, the anti-cavitation plate may be adjustable or shaped to improve plane, and it often has a speed or temperature sensor (thermostat) attached to it.
Damage to the edge of the anti-cavitation plate (burrs, dents) can create turbulent flows that reduce the efficiency of the screw. If defects are detected, the surface must be cleaned and leveled.
Typical malfunctions and their signs
The lower part of the motor is the most exposed, so failures are the most common, and understanding the symptoms helps to quickly diagnose the problem, for example, an extraneous noise in the gearbox area may indicate wear of bearings or gears.
⚠️ Warning: If you notice a high-revving vibration, immediately turn off the gas, which may be a sign of damage to the propeller blades or a shaft imbalance, leading to the destruction of the lower unit.
Another common problem is the oil rainbow on the water behind the boat, which indicates that the gearbox oil is being leaked into the water through the damaged seals, and ignoring this feature will lead to dry gears and costly repairs.
Regular visual inspection of lower unit after each trip allows you to identify minor damage and prevent major accidents on the water.
Also worth mentioning is the overgrowth problem: in warm water bodies, the bottom of the motor is overgrown with seashells and algae, which increases resistance and worsens cooling, mechanical cleaning and the use of anti-fouling coatings (compatible with aluminum) solve this problem.
Rules of operation and storage
A number of rules must be followed to extend the life of the lower part of the engine. After each trip in salt water, lower unit should be thoroughly washed with fresh water.
When transporting a boat in a trailer, it is better to fold or remove the engine to avoid vibration loads on the mounting units of the lower unit. Prolonged vibration can lead to microcracks in the casting.
- 🛡️ Use a transport propeller or prop to take the load off the lower unit when parked on shore.
- 🧼 Wash the motor with a soft brush, avoiding the use of aggressive chemicals that can damage the paint.
- 🔧 Regularly check the tightening of the bolts of the lower unit mount to the lower unit pipe.
Storage of the motor must be upright, so that the osteoils can be deformed and oil or water can be leaked out of the nodes, and slanted storage is only allowed for short periods of time.
What to do if water gets into the gearbox?
If you find water in the gearbox oil (emulsion), you need to immediately stop operating. The motor needs to be delivered to the service or completely disassemble the gearbox yourself, wash all the parts with gasoline, replace the glands and seals, and then reassemble with the oil change. Operating with water inside will corrosion of gears and bearings in a matter of hours of operation.
How often should you change the oil at the bottom?
Manufacturers recommend changing the oil in the gearbox once a season or every 100 motor hours, but if you often walk in shallow water or in difficult conditions, it is worth checking more often.
Can I paint lower unit by myself?
Yes, you can, but you need special training, you need to clean, degrease, and coat aluminum with non-ferrous metals, ordinary paint will quickly peel off, there are special aerosols to restore the coating of lower unit, which are resistant to water and shock.
Why is the lower part of the motor buzzing in neutral gear?
The buzzing on the neutral often indicates wear of the propeller shaft bearings or improper adjustment of the gaps in the gears of the gear gear gears, and cavitation can also be the cause if the anti-cavitation plate is damaged or the motor is installed too high.
⚠️ Warning: Never try to test the engine out of water without a special capacity or cooling system. Dry work can melt the impeller pump and deform the exhaust parts even for a few seconds.
Knowing what the bottom of the outboard motor is called and what it consists of is the first step to mastering navigation. lower unit, gearbox, propeller Careful treatment of these units ensures that your motor will last for many years, delighting with reliable traction and stable operation on any water bodies.