Suddenly hitting the bottom of the engine is a nightmare for any owner of a water appliance, which can turn a pleasant walk into an expensive repair. The knock and vibration that occur when the engine is running with an emulsion in the crankcase often indicate that tightness is not a problem. drive-shaft To avoid major repairs, experienced water-engineers regularly perform a pressing procedure that allows you to detect the slightest air leakage long before the fatal water hit.
The process of checking the tightness of the transmission does not require complex stationary equipment and is quite feasible in a garage or even on the shore of a reservoir with a minimum set of tools. The essence of the method is to create excessive pressure inside the closed volume of the gearbox and visually control its preservation using soap solution or immersion in water. sealing will help to save the life of expensive gears and bearings, preventing their corrosion and jamming.
Before you start manipulating the air compressor, you need to clearly understand the physical nature of the processes and design features of the unit. The gearbox is a sealed case filled with a special transmission oil that lubricates the gears and removes heat. In the normal mode of operation inside the body, when heated, a slight excess pressure is created, which must be drawn through the sapoon, but when cooling or parking, the system must be absolutely sealed to prevent water suction.
Pressures reveal not only obvious damage to the osteoils, but also microscopic cracks in the body or defects in the gaskets, which are invisible during external inspection. If you ignore the need for inspection, the emulsified oil loses its lubricating properties, which leads to rapid wear of the pair. gear The water that gets in causes corrosion of metal parts, which progresses even during the storage of the engine in the off-season.
⚠️ Warning: Never create pressure in the gearbox without first draining the remnants of old oil and not making sure the cleanliness of the drain holes, as the dirt that gets inside can instantly block the lubrication channels.
Necessary tools and workplace preparation
A good workplace and a specialized tool are key to successful diagnostic work. You will need a compressed air source, which can be a conventional car compressor for pumping tires or a more efficient garage installation. A pressure gauge with a sufficiently large scale that allows you to accurately control the pressure generated, which usually does not exceed 0.6-0.8 atmosphere for most models, is critical.
To seal the drain holes, you need to make or purchase special adapters, because regular plugs are not designed to connect the air supply hose. Often homemade plugs from old spark plugs or specially sharpened bolt holes with a drilled channel are used. You will also need a container of water of sufficient volume to fully submerge the bottom of the lower unit, or a spray gun with soap solution for local inspection.
☑️ Preparation for pressing
Keep in mind personal protective equipment and cleanness of the process, as working with oils and chemicals requires carefulness. Prepare the rags to remove oil residues, the tank for waste liquid and gloves so as not to stain your hands. If you plan to use industrial nitrogen instead of air, make sure that the gearbox and all its elements are completely fat-free, since oil and nitrogen can form explosive mixtures under certain conditions, although this is rare in the home.
Use a transparent silicone sealant to temporarily fix homemade adapters on the plugs, this will eliminate air leakage through the thread during the test.
Technology of adapter creation and sealing
The most difficult step for a beginner is often to make a reliable adapter that will connect the compressor hose to the drain hole of the gearbox. Standard plastic or aluminum plugs have conical threads and do not provide tightness when air is supplied from the outside without additional tricks. The most common solution is to use a metal plug into which a nipple is brewed or pressed from the car camera, or use an old spark plug with a remote central electrode.
When using candlestick method, you need to choose a candle, the thread of which coincides with the threading of the drain hole of your engine, which is often found in Yamaha and Mercury engines. The internal ceramic insulator and electrodes are neatly knocked out, after which a hose is passed through the hollow center or a fitting is inserted, and the joints are abundantly sprayed with a sealant. It is important that the design withstands the pressure of at least 1 atmosphere without breaking down, so all threaded connections are better further fixed.
Alternatively, the use of ready-made factory adapters, which are sold in specialized spare parts stores for outboard motor. Such devices often have rubber seals and a clamping mechanism, which allows you to quickly seal the hole without the use of threaded adapters. However, the versatility of such devices is limited, and for motors with a non-standard location or size of traffic jams. drainhole You'll still have to be smart.
| Adapter material | Difficulty of manufacture | Reliability | Universality |
|---|---|---|---|
| The old spark plug. | Medium | High. | Low (you need to pick up the thread) |
| Staff plug + nipple | High (welding required) | Very high. | Medium |
| Rubber cap with clamping | Low. | Medium | High. |
| Factory adapter | Missing. | High. | Depends on the model. |
Step-by-step process of reducing the
Once all the preparatory work is completed and the adapter is installed, you can start directly creating pressure in the system. Connect the compressor hose to the adapter and start slowly supplying air, carefully watching the pressure gauge. Pressure should be raised smoothly, avoiding sudden jumps that could damage the glands, and stop the flow when you reach a value of 0.5-0.6 bar, which is sufficient for diagnosis.
If you use the immersion method, carefully lower the bottom of the lower unit into the water tank so that the liquid level covers all potentially problematic areas: the exit of the paddle shaft, the junction of the case and the lower unit. If you use a soap solution, apply abundant foam on all seals, glands and threaded joints, waiting for bubbles to appear. Even small, rare bubbles indicate a leakage that requires immediate intervention.
What to do if the bubbles come from under the coil of the paddle shaft?
This is the most common malfunction, and it requires a replacement of the osteoil, and it requires removing the locking ring, removing the old osteometer, cleaning the seat, and gently pressing the new one, oiling the working edge of the osteoart.
It is important to withstand the pressure reducer for 3-5 minutes, as some manifest leaks do not immediately occur. If the pressure on the pressure gauge begins to fall, but there are no visual bubbles, perhaps air escapes through a microcrack in the body or a loosely closed upper stopper. In such cases, it is recommended to recheck all connections and, if necessary, increase the pressure to 0.8 bar, but not exceeding the maximum permissible values for a particular model of the motor.
Stable pressure for 5 minutes and the absence of bubbles in water or soap foam is the main sign of serviceability of the gearbox seals.
Diagnostics of malfunctions and search for leaks
The analysis of the bubbles' exit site allows for precise identification of the type of malfunction and the amount of repair work required. If the air comes out from under the lower osteoil, this indicates wear and tear of the working edge of the paddle shaft seal, which often happens after winding the line or hitting underwater objects. The upper osteologic, which is responsible for sealing the drive shaft, usually fails less often, but its replacement requires a deeper disassembly of the knot and removal of the locking rings.
Particular attention should be paid to the condition of the gasket between the gearbox body and the lower unit, as its damage can lead to a mixing of oil and water in large volumes. Cracks in the body of the lower unit, especially in the area of the attachment of the anti-cavitation plate, are often the result of severe impacts and may not be visible without careful cleaning of the surface from dirt and paint. Sometimes leakage occurs through the threading of drain plugs, if they have chips or bullies.
In rare cases, air can pass through the lubrication system if it is structurally connected to the inner cavities, or through casting defects. If visual inspection does not reveal obvious damage, but the pressure drops, you can use the method of adding dye to the oil after assembly, but this is a method of post-facto verification. For accurate diagnosis of cracks in the metal, ultrasonic inspection or capillary defectoscopy in specialized workshops is sometimes used.
⚠️ Attention: If during the pressing you heard a characteristic click and the pressure dropped sharply, there may have been a failure of the osteum or a collapse of the seal, which requires a complete dismantling of the node.
Oil Replacement and Final Assembly
After successfully passing the leakproofness test, the procedure must be completed correctly by removing moisture residue and filling the gearbox with fresh oil. The oil should be poured through the bottom hole until it starts to flow out of the top hole, which ensures complete displacement of air from the system. Using a special pump or syringe facilitates this process and prevents the formation of air stoppers that can lead to oil starvation of the gears.
The gearboxes of outboard motors use special API-labeled GL-5 transmission oils to lubricate them, which have the necessary anti-shoot properties, and it is important not to confuse them with motor oils, as these do not contain the right additive package for hypoid gears and can cause the gear teeth to get kicked. The amount of oil depends on the model of the motor, and its exact value is specified in the operating manual.
When you twist the plugs, you have to follow the right order: first, the top plug is twisted, then the nose of the syringe is quickly removed from the bottom hole and the bottom plug is twisted. This algorithm creates a slight thinning inside the gearbox when cooling, which is an additional barrier to water penetration through the coils. It is recommended that the corks be lubricated with lithium lubricant or a special sealant to prevent corrosion and facilitate unwinding in the future.
Why can the oil turn white after a few hours?
This is a sign that water has entered the gearbox. If the pressing has not revealed any problems, it may have been through the sapoon when the hot gearbox cools sharply (for example, when entering cold water) or through a microcrack that opens only when vibrating.
Frequent errors and prevention measures
One of the most common mistakes is the use of excessive pressure during pressing, which can lead to the extrusion of the osteoils and the need to replace them even on a working node. Pressure above 1 atmosphere is not required for diagnosis, and the risk of damage to the seal increases many times. It is also a mistake to ignore the purity of the drain holes: metal shavings accumulated on a magnetic cork can damage the osteoil mirror during installation or create a leakage channel.
Many owners forget to change the oil in the gearbox every year, believing that it is filled forever, which is a gross violation of the rules of operation. Over time, the oil loses its properties, becomes saturated with moisture and microparticles of metal, turning into an abrasive paste that accelerates the wear of parts. Regular oil replacement and visual monitoring of its condition (no emulsion) is the best prevention of serious breakage.
To extend the life of the gearbox, avoid sharp gassings when the gear lever is neutral, as this creates impact loads on the gears. It is also important to monitor the condition of the lower unit: chipped paint and scratches should be painted over immediately to prevent corrosion, which can eventually develop into a through crack. Regular inspection of the knot after each release will help identify problems at an early stage.
What pressure is considered normal during pressure?
The optimal pressure for checking the tightness of the gearbox of the outboard motor is considered to be a range from 0.5 to 0.8 atmosphere (bar). Pressure above 1 atmosphere is not recommended, as this can damage the osteoils.
Can I use a car compressor?
Yes, a conventional car tire compressor is quite suitable for this task, because it can create the necessary pressure, the main thing is the presence of a pressure gauge for control.
What if the oil in the gearbox turned white?
The white color of the oil (emulsion) indicates that water has entered. You need to immediately stop operation, disassemble the gearbox, find and eliminate the cause of the leak (replace the gums, gaskets), wash the knot and replace the oil.
How often should you change the oil in the gearbox?
It is recommended to change the oil in the gearbox at least once a year, preferably before the start of the season or after it ends.