A sudden knock at the bottom of the outboard motor or the appearance of an emulsion in the crankcase can spoil any launch. Boat gearbox It's a complex mechanism that transfers torque from the crankshaft to the propeller, and failure often happens at the most inopportune moment, and ignoring the first symptoms of wear can lead to jamming of gears and costly overhaul of the entire lower unit part.
Timely diagnosis can identify the problem at an early stage, when simple replacement of osteoils or adjustment of gaps is enough. In this article, we will discuss in detail the lower gear device, defect methods and step-by-step algorithm for restoring the operability of the node. Yamaha, Mercury and Tohatsu They are similar in design, so the principles of service will be relevant for most brands.
Don't be afraid to open the machine yourself, if you have a basic set of tools and a clean workplace. tightness And the precision of the assembly is crucial, because any grain of sand that gets inside can disable expensive bearings in a matter of hours of loading.
Diagnostics of transmission failures
The first sign of impending trouble is often a change in the color of the oil during scheduled maintenance, and if instead of a clear or slightly yellowish liquid, you see an emulsion of the color "coffee with milk", then water has entered the housing. tightness stains or stains that require immediate intervention.
Noise and vibration when working at idle or high speeds are also alarm bells. Knocking can indicate wear of gear teeth or destruction of rolling bearings. In some cases, the hum only appears when changing gears, which indicates problems with the mechanism of switching. dog clutch.
⚠️ Warning: The operation of a motor with signs of water entering the gearbox is strictly prohibited. The water washes out the lubricant, and the dry operation will destroy the gears and bearings in a few minutes.
For accurate diagnosis, you need to conduct an external examination of the lower unit for cracks and dents, even small damage to the housing can disrupt the geometry of the bearing seats, and check the condition of the lower unit shaft for backlashes by shaking the screw with your hand.
Essential tools and supplies
Quality repairs are impossible without a specialized set of tenants and measuring tools. A standard garage set is often not enough, since many components require careful pressing. Particular attention should be paid to cleanliness - not a single speck of dust should enter the gearbox.
You will need a dynamometer key to tighten the bolts to the accuracy of a newton meter. Using conventional keys "by eye" can either cause the threads in the aluminum case to break down or to squeeze the gaskets under pressure.
- 🛠️ Removal of bearings and locking rings (shallable type).
- 🔧 A set of probes to measure the gaps between the gears.
- 💧 Specialized oil for gearboxes (usually GL-4 or GL-5 labeled for marine use).
- 🧪 Sea sealant for marine engines (no acidic, usually gray or black).
- 🧹 Solvent for degreasing surfaces before assembly.
One of the important things to mention is the importance of using original or quality parts, and cheap Chinese oils can suffocate after the first season, which will lead to water ingress again. O-rings must be made of material resistant to oils and sea salt.
Always buy a full seal kit for your engine model. Buying individual ossils often results in some small seal remaining old and causing a leak.
lower unit disassembly process
Disassembly begins with the removal of the lower unit from the main engine unit, which requires the unplugging of the gear thrusts and the unscrewing of the fasteners. Johnson/EvinrudeIt may be necessary to remove the locking ring before dismantling.
After the lower part is separated, the screw shaft should be carefully removed along with the switching mechanism. It is important not to lose small parts such as springs, bracket balls and adjusting washers. It is recommended to take photos of each stage or arrange the details in the order of their removal.
Sequence of withdrawal:1. drain the oil and assess its condition.
2 Unscrew the bolts of the lower unit mount.
Remove the locking ring of the switching shaft.
4. Gently pull the screw shaft down.
Then there's the pressing of the bearings and the removal of the gears, which uses heating the body with a building hair dryer to about 100-120 degrees Celsius, and then the sharp heating allows you to expand the aluminum and it's easier to remove the pressed parts without damaging the seats.
⚠️ Warning: When heating the case, do not direct the jet of hot air directly onto the glands or plastic cells if they are not already removed, this will cause them to melt and deform.
Defection and evaluation of details
Once completely disassembled, all parts must be thoroughly washed in salvent or kerosene, visual inspection allows you to identify chips, bullies and corrosive spots, pay special attention to the teeth of the gears - they should have a smooth working surface without cutting.
Wearing bearings is checked by swaying the clip and listening to the rotation, and even a few microns are not acceptable for high-speed knots. Bearings They should rotate silently and smoothly, without jerks and jamming.
The shafts are tested for beat with an indicator rack, and the curvature of the screw shaft or the lower unit shaft leads to rapid destruction of the ossels and uneven wear of the gears, and if the shaft has traces of corrosion under the oss, it must be traversed or replaced.
| Verification parameter | Permissible value | Method of measurement | Consequences of excess |
|---|---|---|---|
| Axial engagement of gears | 0.15 - 0.35 mm | Setting of probes | Noise, overheating, toothpainting |
| Beating the shaft | Max. 0.05 mm. | Time-type indicator | Destruction of the ossels, vibration |
| Gap in bearings | Missing. | Tactile/hearing | Knock, jamming the knot. |
| The depth of the grooves of the ossels | No production. | Visual/micrometer | Water and oil intrusion |
If pitting pitting pits (small dots) are found on the gears, this is a sign of metal fatigue or working with contaminated oil. Single points on the non-working surface may be permissible, but on the working part of the tooth - this is an excuse to replace a pair of gears.
What is pitting?
Pitting is the fatigue of metal staining on the surface of the gear wheels, due to cyclic contact stresses, and if the pitting area is greater than 2-3% of the working surface, the gear needs to be changed, as the process will progress rapidly.
Convertible assembly and clearance adjustment
The assembly is done in reverse order, but with special rules, all rubbing surfaces are abundantly lubricated with special molybdenum or lithium lubricant before installation, which provides protection from dry friction in the first seconds of starting the engine.
The critical step is to install adjustment washers under bearings, which determine the correct engagement of gears and the absence of backlashes, and the thickness of the washers is selected experimentally or calculated using the manufacturer's formulas using a micrometer to measure.
- 📏 Measure the total height of the package of parts in the case.
- 📏 Measure the distance to the persistent burt in the body.
- 📏 Calculate the thickness of the washer required to provide the tension.
- 📏 Set the selected washer and check the assembly for twisting.
When installing the oil oils, it is important not to damage their working edge. Before installation, lubricate the edge with oil, and plant the oil oil itself strictly evenly, using a mandrel of the appropriate diameter. Distortion of the oment during pressing will lead to instant loss of leakage.
⚠️ Warning: Never use a sealant to fix the ossels inside the seat. The osselnik is held by tension; the sealant can get to the working edge and cause leakage.
☑️ Control assembly of gearbox
Pressurization and testing
After assembly, the body must be tested for leakage, without placing a lower unit on the motor, using a compressor with a pressure gauge and a device to create a vacuum or pressure in the crankcase of the gearbox. The standard pressure for inspection is usually 0.6 - 0.8 atm (or 7-10 psi).
The assembled gearbox is immersed in a container of water or lubricated abundantly with soapy solution. When applied, the appearance of air bubbles will indicate the location of the leak, most often "poisoning" around the perimeter of the lid or around the lower unit shaft.
If the gearbox keeps the pressure for 15 to 20 minutes, you can pour the oil, the oil level is checked through the bottom hole, it should appear as soon as the level reaches the cut, the top hole serves to release air.
The main criterion for high-quality assembly is that the gearbox holds vacuum and pressure, and when the shafts are rotated, there is no backlash and extraneous noise.
The final step is to put a lower unit on the engine and test it in a barrel of water. Pay attention to the thermostat (if it's in the cooling system of lower unit) and the absence of vibrations. The smoothness of the gear shift confirms that the mechanism is properly assembled. shift dog.
Frequently Asked Questions (FAQ)
How often should you change the oil in the gearbox?
The gearbox oil should be changed at least once a season, ideally before and after winter storage. If you notice an emulsion, you should replace it immediately after eliminating the cause of the water intake. Regular replacement allows you to wash out the wear products and maintain lubricating properties.
Can I use car transmission oil?
The GL-5 car oils contain sulfur additives that can be aggressive against non-ferrous metals (brass bushes) often used in boat gearboxes. It is better to use specialized oils labeled "Marine" or "Hypoid Gear Oil" without aggressive additives.
Why do the screw blades bend?
This is most often the case when you hit an underwater obstacle, but if the propeller bends constantly, it may indicate that the screw is not correct. lower unit Or the engine's cavitation mode, and it could also be because of a mismatch in the pitch of the motor's power propeller.
Do I need to smear the screw shaft before installation?
The screw shaft and gear shaft must be lubricated with corrosion-resistant lubricant (usually bundled with the motor or bought separately) to prevent the shaft from being boiled and to make it easier to remove the screw in the future if repairs are needed.