Every water motor, even experienced, sooner or later faces a situation where needed to use the water. boat-motorThis can be a routine procedure to change the type of propeller to improve speed performance or a forced measure after a collision with an underwater obstacle. Understanding the principles of dismantling and installation is critical for safety on the water and preserving the life of your transmission. outboard.
Ignoring propeller damage can have serious consequences. Vibration transmitted to lower unit can destroy the ossels, damage bearings and even cause cracks in the gearbox body. So timely diagnosis and proper replacement of elements is not just a matter of aesthetics, but a necessity for long-term service of the equipment.
In this article, we will discuss in detail the algorithm of actions, necessary tools and typical errors in the maintenance of the screw group, you will learn how to act if the nut boiled, and how to choose the right screw for your boat.
Diagnostics of propeller condition
A thorough visual inspection is required before a physical dismantling is carried out, and often the external damage is obvious: chipped edges of the blades, deep scratches or deformation of the geometry, but there are also hidden defects that may not be visible at first sight, but significantly affect the operation of the engine.
Particular attention should be paid to the state of hub And it's through this node that the torque is transmitted from the gear shaft to the screw, and if the rubber bushing is twisted or crumbled, the motor will gain momentum, but there will be no traction on the water, or it will be extremely weak, and this is a classic symptom of slippage.
Also check for backlash. Take the blades and try to swing the screw in different directions. The presence of a palpable beat indicates wear of the sleeve joints or the destruction of the sleeve. In some cases, the screw can form microcracks, which, when high loads, can lead to complete destruction of the blade.
⚠️ Warning: The operation of a motor with a damaged screw is prohibited! Vibration from an unbalanced screw can in a matter of minutes disable expensive lower unit bearings.
You can use the defective method to accurately assess the condition of the metal, but in the field, a careful examination is enough. If you notice that the paint on the hub has swelled or detached, this may indicate that corrosion has begun under the coating, which is especially true for aluminum alloys in salt water.
Tools and training required
A good rotor replacement is impossible without a well-fitting tool. The standard set that every boat owner should have in their arsenal includes several key items. The lack of specialized keys can turn a simple procedure into a long-term rust fight.
First of all, you'll need candle-key Or a special head, which is the size of the screw nut. Yamaha, Tohatsu and Suzuki 24 mm turnkey nut, but on older models or engines Mercury You can always check the specification for your particular model.
- 🔧 A cap or end key (head) of the appropriate size is the main tool for unscrewing the nut.
- 🔨 Hammer and core or puncher - necessary to knock out a locking pin or splint.
- 🛢️ Lubrication (lithium or graphite) - for processing the shaft and threaded joints before assembly.
- 🧤 Tight work gloves – The screw blades can be razor sharp even if they look smooth.
It is also recommended to have under WD-40 Or a similar penetrating lubricant, which is needed if the screw attachment nut is "stiffened" due to prolonged contact with water and oxidation of metals, and also a wooden bar or a stop to fix the screw from turning when unscrewing.
Prepare clean rags to remove old lubrication and dirt from the shaft. Abrasive sand particles between the screw hub and the shaft can lead to bullying on the polished surface of the shaft, which in the future will complicate dismantling.
☑️ Ready to replace the screw
Step-by-step instructions for dismantling
The process of removing the propeller begins with safety: the motor must be raised to the highest position or securely fixed on the transom so that the propeller does not touch the ground or the bottom of the pier. If the boat is on water, make sure that it is on the anchor or securely moored, as there is a chance of a jolt when working with the tool.
The first step is always to remove the locking element. Depending on the design, it can be ploughpassing through the nut and shaft, or separate lock-pin The splint is not reused after removal, it must be replaced with a new one.
Then there's the unscrewing of the mounting nut, and it's important to remember the direction of the thread. Most outboard motors have right threads (unfolding counterclockwise), but some models have the right thread. Mercury And old Japanese engines may have left-handed threads, so if the nut doesn't work, don't put too much effort right away -- treat the joint with penetrating lubricant and let it stand for 10 to 15 minutes.
Procedure:Remove the locking washer/pin.
2. to process the WD-40 nut (if required).
3. Lock the screw from the twist.
4 Unscrew the nut (usually counterclockwise).
5. Remove the persistent washer and the screw itself.
Once the nut is removed, carefully remove the thrust washer (the puck of a thrust bearing) which is of a specific shape and must be mounted on the correct side of the assembly. Then, when you take the hub, pull the screw on yourself. If the screw is sitting tight, you can sway it slightly from side to side. It is forbidden to knock a metal hammer on the shaft or blades - use a soft metal embroidery or wood.
What to do if the nut does not unwind?
If the screw nut is stuck, don't try to rip it off with a jerk, risk breaking the shaft's slats. Pour the joint with penetrating lubricant and leave it for 30-40 minutes. You can try to carefully warm the nut with a building hairdryer (not open fire!) to expand the metal. If that doesn't help, you'll need a special tool, a screw remover, which rests on the end of the shaft and pushes the screw by rotating the nut or a special bolt.
Checking of the veneer and hub hub hub sleeve
Once the screw is removed, the critical stage of internal component diagnostics begins. slab-line It's a small metal rod that transmits rotation, and its condition directly affects the reliability of the stroke.
Remove the veneer and inspect it carefully, if it has crumpled, deformed or slicked faces, it must be replaced. Using a deformed veneer will cause the screw hub to break rapidly, and then you will have to change the screw itself. The veneer is disproportionately less than the cost of a new screw, so change it at the slightest doubt.
The second important element is rubber-sleeve It's a safety lock, and when it hits an obstacle, it turns the sleeve around, protecting the gears of the gearbox from breaking, and check if the sleeve is not turning around the hub body, and many screws have special marks or holes on them.
To test the sleeve, you can use a simple test: insert the veneer into the shaft hole and try to turn the screw hub relative to the shaft. If you feel free travel without rubber resistance, then the sleeve needs to be replaced. Also, the sign of a malfunction is the presence of a rubber crumb around the veneer after removing the screw.
⚠️ Warning: Never use nail veneers, wire or drills! Only regular veneers made of special alloy provide the calculated strength and cut when overloaded.
If you find that the slats on the gearbox shaft are damaged (bobbers or licks appear), this is a serious problem. In mild cases, you can carefully clean the bullies with a small topfill, but if you have severe damage, you will need to repair or replace the lower unit.
Selection of a new propeller
Replacing a propeller is a great way to rethink the specifications. A standard propeller that comes with a motor is a compromise solution. It may not be suitable for a particular boat, cargo and skiing style. diameter, step And the number of blades.
A Pitch is the distance that a screw theoretically travels in a single rotation in a solid medium. Increasing the pitch increases the maximum speed, but reduces traction and acceleration dynamics. Reducing the pitch ("reduced") improves the output for planing and traction, but limits the "maximum speed".
The number of blades also plays a role. Three-blade screws are more efficient at high speeds and have less resistance. Four-blade screws provide smoother running, better handling at low speeds and faster lead the boat to planing, but can strangle the engine at high speeds.
When selecting it is important to take into account the recommendations of the manufacturer of the engine. the use of too heavy a screw (big pitch or diameter) will force the engine to work in overload mode, which will lead to detonation, overheating and a reduction in the life of the piston group.
For accurate matching, use the matching tables published by propeller manufacturers, which list recommended combinations of engine power, boat weight, and desired stroke specifications.
Comparison of materials: Aluminum vs. Stainless steel
When you choose a replacement screw, you have to ask the owner what material they need to do. Most of the budget and standard screws are made of aluminum alloys. They're cheap, lightweight, and they're quite plastic. When you hit a rock, the aluminum screw is often just bent, keeping the hub and gearbox intact.
Stainless steel screws (arts.Stainless Steel) are much more expensive, but have a number of advantages: they are stronger, thinner in cross section (which reduces water resistance), and do not suffer cavitation erosion.
But stainless steel has its downsides: If you hit it hard, the power goes further down the transmission, and if you just shoved an aluminum screw, it can screw the sleeve, or at worst, damage the gears of the gear if the protection system doesn't work, and it's harder to drive the steel screws at home.
| Characterization | Aluminum screw | Stainless steel screw |
|---|---|---|
| Cost | Low. | High (3-5 times higher) |
| Strength | Medium (bends when struck) | High (holds the punch) |
| Impact on the gearbox | Careful (breaks itself) | Risk of impact transmission to the shafts |
| Efficiency | Standard. | Higher by 5-10% due to thin edges |
Material choice depends on the operating conditions. For rocks, shallow waters and fishing in overgrown areas, aluminum is better left. For high-speed walks in clean water and long distances, stainless steel will give a tangible increase in speed and efficiency.
Assembly and installation of a new screw
The process of installing a new or refurbished screw is a mirror image of dismantling, but it has its important nuances. The main rule is the cleanliness of the interfaced surfaces. The gearbox shaft should be perfectly clean and lubricated.
Apply a thin layer of waterproof lubricant to the silk part of the shaft, which will prevent corrosion and facilitate future dismantling. But don't overdo it: excess lubrication can create a hydraulic wedge, and the screw will be difficult to plant to the point. Also lubricate the nut thread and the thrust bearing.
Set the screw on the shaft, align the slats. Make sure the screw sits tightly, without skewing. Put the thrust washer on the right side (usually with a burtic to the screw). Wrap the nut from hand to stop. Now you need to fix the shaft from turning. Many motors have a special hole in the casing or use a stop between the blade and the anti-cavitation plate (through a wooden pad!).
Tighten the nut with the key with the effort recommended by the manufacturer. The moment of tightening of the screw nut is usually 50-60 NmBut you can look for the exact data in the manual, and if you pull it, you can damage the thread, and if you don't pull it, you can unscrew it and you can lose the screw.
The final chord is to install a new lock pin or splint, and if you use a splint, spread its tendrils to the sides, but not too wide so that they do not interfere with the flow of water and do not scratch the screw body when you can turn.
⚠️ Warning: After installing the new propeller, be sure to test the launch in shallow water or in a barrel of water, and make sure there is no strong vibration and extraneous noise before going full mode.
Frequently Asked Questions (FAQ)
How often should I change the veneer on the outboard motor?
The veneer doesn't change on schedule, just because it's damaged. If you haven't rammed rocks and the screw hasn't turned, the regular veneer can last for years. However, if you're planning a long trip to the wild, it makes sense to bring 2-3 spare veneers with you, because it's the most consumable part of the transmission when hit.
Can I drill a hole in the nut if I lose the splint?
It's not recommended. The nut is made of hardened steel, and the drilling can split it, and the hole must be strictly aligned with the shaft hole. If the splint is lost, it's better to drive to the store at low speeds (carefully controlling the nut), or use stainless steel wire as a temporary measure, but be sure to replace it with a regular splint at the earliest opportunity.
Why does the screw nut constantly unscrew itself?
Most likely, the thread on the shaft or inside the nut is damaged, or the thrust washer is missing/deformed. Also, the reason may be the absence of a lock pin. Check if the rubber sleeve has turned, in which case the nut may seem tight, but the screw does not spin, creating the illusion of attachment problems.
Does the replacement of the screw affect the engine guarantee?
Self-replacement of the screw is not a reason for removal from the warranty, if you did not damage the engine in the process (for example, did not drop a heavy screw on the lower unit, did not break the thread). However, if the engine breakage is caused by the installation of a non-standard screw with an inappropriate step that led to overload, the service center may refuse warranty repair.