The water inside the lower gear is the surest sign that the tightness of the knot is broken, and if you notice an emulsion when you change the oil or hear an extraneous noise when the screw is working, you can not hesitate. Pressure reduction It becomes the only way to accurately determine the location of the leak and eliminate it before the major destruction of the gears.
The process of checking the tightness requires accuracy and understanding of the physics of the processes that take place inside the crankcase. Yamaha or Mercury They make the mistake of relying only on visual inspection of the ossels, and in fact, microcracks in the casing or pressure cuff wear cannot be detected without special equipment.
In this article, we will discuss how to conduct a quality diagnosis in a garage, you will learn how to make a soap solution properly, how to prepare a soap solution and why. temperature-shift This is a key factor when looking for hidden defects.
Causes of water getting into the reducerBefore you start disassembling and testing, you need to understand where the water comes from, and most often, boat owners experience wear on the propeller shaft glands, which are extremely stressful, especially if the engine often runs at high speeds or in water with a high content of sand.
But mechanical damage is also important, because impacts on underwater obstacles can cause micro-cracks in the gearbox body that are not visible to the naked eye, and may also be caused by the loss of the properties of the sealing rings, which eventually tan and cease to function.
- 🛑 Wear of cuff seals of the paddle shaft due to the natural aging of rubber.
- 🛑 Mechanical damage to the body after contact with stones or logs.
- 🛑 Destruction of sealing rings under the oil drain plug or in the places of docking of nodes.
Required tools and materialsAnd to do this, you're going to need not only a basic mechanic set, but you're going to need a specific set of things, and the key element here is the compressed air source, and it could be a compressor with a receiver or an inert gas cylinder, but it's important to be able to regulate the pressure.
You also need a pressure gauge with an accuracy of 0.1 atmosphere to control the load on the osteoils. Without this device, the pressing turns into a divination on the coffee grounds, where there is a high risk of either not finding a leak or damaging the knot with excessive pressure.
Don't forget to prepare a water tank that you can load the bottom of the motor into, and if you can't, you'll need a spray spray with soap solution, and you'll need adapters to connect the hose to the gearbox drain hole, which are often bundled with service kits for the engine. Tohatsu or Suzuki.
Preparation of the gearbox for inspectionThe first step is always to completely clean the knot of dirt, algae and residues of old oil. Any dirt can hide the release of air bubbles, leading to a false diagnosis. Wash the bottom gear thoroughly with clean water and defat the surface around the corks.
Then you have to unscrew the top and bottom of the oil drain plugs, and you put a compressor hose tip through the bottom hole, and it's important to have a sealed connection at that point, so that the air doesn't come out through the thread, mimicking a malfunction, and you can use rubber cone plugs or special adapters to do that.
☑️ Preparation for pressing
Once you've connected the hose, you need to gently blow the knot to remove the oil from the inside, and then you can start to create pressure, and remember, there's no liquid inside, otherwise the test results will be distorted.
Technology of pressing and search for leaksThe pressure process itself requires strict adherence to pressure parameters. For most two-stroke and four-stroke engines with a power up to 50 hp, pressure in the range of 0.6-0.8 atmosphere (bar) is considered safe.
Plug the bottom of the motor into a water tank so that the liquid level completely covers the area of the paddle shaft and the seal of the switching rod. Watch the surface carefully: the appearance of a chain of bubbles will indicate the depressurization site. If immersion is not possible, apply a profuse soap emulsion to all joints and glands.
The nuances of leaking
If the bubbles appear immediately after air is supplied, it's a major damage, but if they start to appear only after 10-15 seconds, then the air passes through microscopic gaps or pores in the rubber, which also requires replacing the seal.
Pay special attention to the exit area of the paddle shaft, which is where the most common problems occur, bubbles can come from under the ossuary or through the drainage hole (if it is designed and clogged).
Results analysis and parameter tableThe interpretation of the results depends on the pressure behavior on the pressure gauge and visual signs. If the pressure gauge needle is dead and there are no bubbles, the pressure reducer is sealed. A drop in pressure without visible bubbles may indicate a leak in the hidden cavities or a malfunction of the pressure gauge itself.
There may be recommendations for different manufacturers for maximum pressure, exceeding these standards can lead to the compression of seals, and below is a table with indicative values for popular brands.
| Motor brand | Recommended pressure (atm) | Maximum pressure (atm) | Typical problem |
|---|---|---|---|
| Yamaha | 0.6 - 0.7 | 0.8 | Wear of the oal shaft |
| Mercury | 0.5 - 0.6 | 0.7 | Cracks in the body (old models) |
| Suzuki | 0.6 - 0.8 | 0.9 | Swelling of sealing rings |
| HDX / Hidea | 0.5 - 0.6 | 0.7 | Poor quality of gum rubber |
Use nitrogen instead of air for pressing, if possible. Nitrogen is inert and free of moisture, which eliminates the risk of corrosion inside the gearbox during diagnosis.
Frequent mistakes in self-repairOne of the most common mistakes is ignoring the temperature regime: gum oil changes its properties in the cold and when heated, and checking the cold engine may not reveal leakage that will manifest at operating temperature.
And many people forget to check the integrity of the plugs themselves and their threads. Sometimes the air comes out not through the odule, but through a broken thread or a crack in the aluminum cork.
⚠️ Attention: Never create pressure above 1 atmosphere without the extreme necessity and understanding of the design. The interior partitions of some gearboxes are not designed for high pressure and can deform.
Another mistake is using harsh chemicals to look for leaks instead of soapy solution, and some solvents can damage the rubber parts of the omentums, creating a problem where there was none.
Replacement of seals and finishing assemblyIf a leak is found, the appropriate elements must be replaced. The replacement of the propeller shaft glands usually requires a removable and a mandrel to press the new cuffs, and it is important to set them strictly in the center and at the correct depth specified in the service manual.
When assembly, use only the recommended rubber seal lubricants, which will make it easier to install and prolong the life of new parts, and after replacement, be sure to repress to make sure the repair is successful.
Quality pressing after replacing the osteoils is a mandatory step to ensure that you do not encounter water in the gearbox in the middle of the reservoir.
⚠️ Attention: When installing a new osil oil, never lubricate it with solidol or lithol unless specified in the instructions. Refining products can cause rubber to swell. Use special silicone lubrication.
FAQ: Frequently asked questions
Can the gearbox be pressed with a car pump?
Technically possible, if the pump has a pressure gauge and is able to create a pressure of at least 0.5-0.6 atm. However, foot or cheap hand pumps often cannot provide a stable airflow to detect small leaks, and the process will take a long time.
What oil should I pour after the pressing?
After checking and troubleshooting, you need to fill the transmission oil of the appropriate viscosity (usually 80W-90 or 85W-140) with the API class GL-5.
Why does the pressure drop, but there are no bubbles in the water?
This could mean that air escapes through a microcrack that has closed under the action of water (valve effect), or leakage occurs in the cavity of lower unit, where air comes out slowly.
Do I need to heat the gearbox before checking?
Yes, it's recommended. A warm body and warmed oils are better at mimicking working conditions, so you can idle the engine in a barrel or just leave it in the sun before you start.