The bottom of the outboard motor, which is often referred to as the "boot," is technically called the bottom slab or the lower unit, and this is where the transmission that transmits torque from the engine to the propeller and the gearshift system are concentrated. The gearbox It is under enormous stress, working in an aggressive aquatic environment full of abrasive particles and corrosive agents.
Any malfunction in this area can turn a pleasant walk into an emergency situation requiring expensive evacuation to shore. diagnostics This prevents fatal breakdowns of gears and shafts.
In this article, we will discuss in detail the design of the bottom plate, the algorithms for troubleshooting and the procedure for replacing consumables. lashing is a critical signal and how to choose the right sealant for assembly of the node.
The design and working principle of lower unit
Visually, the boot is a streamlined aluminum or magnesium shell, inside which a complex mechanism hides. gearbox, consisting of a set of gears that ensure the transmission of rotation and change the direction of thrust when reversing.
The vertical shaft connects the crankshaft of the engine to the horizontal shaft of the propeller, and between them is a gearshift system controlled by thrusts or cables from the crankshaft. plumbing And the O-rings.
The body of the lower unit not only protects the machinery, but also serves as a support for the attachment of the propeller and the lower unit pipe, and inside there are channels to draw water used to cool the engine.
⚠️ Warning: Aluminum alloys used in the production of lower unit are susceptible to electrochemical corrosion. Always check the condition of zinc protectors (anode) before each season.
To understand the extent of damage, it's important to know which nodes are most vulnerable, and usually problems arise in the interconnection of moving parts.
- 🔩 Salmon The first take a blow from sand and silt, losing its tightness.
- ⚙️ Scooterney. - suffer from shock loads when hitting underwater obstacles.
- 🌊 Water intake - often clogged with algae, which leads to overheating of the engine.
When storing a boat on water in salt water, be sure to use a lower unit shower to flush the internal salt cooling system.
Typical malfunctions and their symptoms
An experienced boater can identify the problem before removing the boot from the transom, and the first alarm is often a change in the sound of the engine or the appearance of vibration.
If you notice that the engine has stopped developing full power or the screw is idling when dialing, most likely, the problem lies in the coupling Visual examination of lower unit can reveal oil leaks or mechanical damage to the body.
Special attention should be paid to the color of the exhaust gases and the presence of an emulsion. White smoke or "mayonnaise" on the gearbox probe indicates that water enters the body.
Diagnosis should be carried out methodically, excluding one after another possible causes.
- 🔊 Extraneous noise - indicates wear of bearings or lack of lubrication.
- 💧 Oil leak - indicates the destruction of seals or a crack in the body.
- 🔄 Difficult switching - a problem in adjusting the cables or wear of the curtain.
Dismantling the lower plate: step-by-step instructions
The process of removing the boot requires careful preparation and the presence of a special tool. Before starting work, you must disconnect the fuel line and control cables if the design of the engine does not allow you to remove lower unit with them.
First, the oil is drained from the gearbox, and this is done by twisting the top and bottom plugs, and it's important to collect the waste liquid into a container for later disposal, because it's forbidden to drain into the water.
Then you unscrew the lower unit bolts to the middle of the engine, and they range from 4 to 8 pieces depending on the power and model of the engine, and when you remove the fastener, the lower unit gently descends.
☑️ Preparations for dismantling
When the lower plate is separated from the lower unit pipe, light swaying may be required. Do not use excessive force to avoid damaging the gaskets and seals.
The moment of tightening of the bolts of the lower unit fastening: 35-45 Nm (check in the manual of a particular model)⚠️ Warning: When removing the lower unit, make sure the gear lever is in a neutral position so as not to break the backstage mechanism.
Defection of nodes and replacement of osteologies
Once the boot is disassembled, the gearbox's interiors are accessed, the gears are visually inspected first for chips, scaling and bullies, and the teeth are smooth and shiny.
The bulk of the work is usually to be replaced. sludgeOld seals are carefully removed to avoid damaging the landing sites. New glands are recommended to be lubricated with lithium lubricant before installation to facilitate planting and initial operation.
The shafts are tested for beat and corrosion, and even small production at the site of planting the oal can cause future leakage, and if deep risks are detected, the shaft must be replaced or restored.
The table below will help to orient in the main parameters in case of defect:
| Element | Norma. | Critical wear and tear | Action. |
|---|---|---|---|
| Gap's gear. | 0.10 - 0.25 mm | > 0.40 mm | Couple replacement |
| Beating the shaft | < 0.05 mm | > 0.10 mm | Replacement of the shaft |
| Fabular hardness | elastic | Fossil/Cresnull | Mandatory replacement |
| Bearings | Silent rotation | Luft/Crunch | Replacement |
How to check the tightness of the oil seals without disassembly?
There's a vacuum test, you put a pressure gauge on the oil drain, you create a pressure, and if the pressure gauge is running, the glands are leaking air (and water).
Assembly of the gearbox and selection of lubricant
The assembly of the boot is a process that requires purity and precision. All parts must be cleaned of old lubrication and abrasive. transmission oilsThey have high adhesion and water-repellent properties.
When installing the glands, it is important to follow the direction of installation, often with markings or bevels on the body indicating the correct side, and an error in installation will lead to instant oil extrusion.
The junction of the lower unit and the lower unit pipe is sealed with a special marine sealant, it must be resistant to oil products and salt water, the thickness of the sealant layer must be minimal to ensure that metal surfaces fit tightly.
The moment of tightening of the bolts must meet the manufacturer's specification. The retraction can lead to deformation of the body, and the short-tightness can lead to loss of leakage.
Use only original pads or high-quality analogues. Homemade pads made of cardboard or paronite in an aquatic environment quickly break down.
Testing and testing after repair
After assembly, the boots must be installed on the engine and pre-tested. Turn on the transmission on the hung motor (safety!) and listen to the gearbox.
No extraneous noise or vibration is a good sign, but the final leakproofness test is best done under load, so you put the motor in a tank of water (barrel or pool) and let it run in different modes.
After the first release, be sure to check the level of oil in the gearbox. If it fell or the oil changed color, you will have to repeat the disassembly procedure.
- 👀 Visual control Check the joints for oil drops.
- 👂 Audio control Listen to the change in the tone of the engine.
- 🌡️ Temperature conditions Make sure that the lower unit does not overheat.
⚠️ Warning: Do not test the gear shifting on drying at high revs. This can cause the switching clutch teeth to break due to lack of spray lubrication.
FAQ: Frequently asked questions
How often should you change the oil in the gearbox “boot”?
It is recommended to change the oil in the gearbox once a season or after every 100 hours of operation. If you notice an emulsion (white oil), you should make a replacement immediately, first eliminating the cause of the water intake.
Can I use car transmission oil?
Specialized oils for outboard motors contain additives that prevent oxidation in contact with water and protect non-ferrous metals (bronze gears), which are often used in gearboxes.
What if the screw wound a fishing line on the rampart?
You need to remove the screw and carefully clean the shaft. If the line penetrated under the obble, it will have to be replaced, since the line breaks the tightness and can damage the working edge of the seal when the shaft is rotated.
Why does lower unit heat up when the engine is running?
Heating the lower part of the motor may indicate clogging of cooling channels, malfunctioning of the water pump (impeller) or operation of the motor without load on land. Prolonged overheating leads to deformation of the osteoils and jamming of the piston group.