How to change the screw on the outboard motor: full instructions

Replacing a propeller is one of the most frequent and necessary procedures in the operation of any boat, whether it is an inflatable PVC boat or a massive boat. Hitting an underwater obstacle, winding a fishing line or banal wear requires immediate intervention, since a damaged propeller not only reduces speed, but also creates a dangerous vibration that destroys lower unit.

Many beginners mistakenly believe that the process is trivial, but there are critical nuances to ignore that can lead to expensive gear repairs. In this article, we will examine not only the mechanics of replacement, but also the subtleties of selecting the geometry of the blade, as well as the rules for tightening the fasteners that ensure that the knot does not understand on the go.

Before starting work, you need to prepare the workplace and tools, because quality training You'll need access to a flat, hard surface to keep the motor from wobbling, and a basic set of keys and specific fixtures, which we'll talk about later, and remember that working with heavy lower unit requires caution.

Preparation of tools and security measures

The first rule of any repair on the water or in the garage is safety. The engine must be securely fixed and the boat's snag is stable. If you change the screw on the shore, make sure that the engine is lowered and standing on a solid stand or a wooden bar so that the blades do not touch the ground and dull. Never do work if the engine is in limbo without additional insurance.

You'll need a standard toolkit to dismantle, but there's one specific element that you can't do without. screw-pin Or a special key that prevents the shaft from rolling when the nut is unscrewed, and without this device, you risk tearing the edges off or damaging the veneers, which will turn a simple replacement into a complex repair.

• 🔧 A set of end heads and collars (usually 22 mm or 24 mm).
• 🔨 Hammer and squirt (to knock out the stopper pin).
• 🧴 Graphite lubricant or anticorrosion spray for threading.
• 🧤 Tight working gloves to protect the hands from sharp edges.

⚠️ Warning: Before starting work, be sure to disconnect the candle caps or remove the fuse responsible for starting the engine. Accidental start of the engine when you have your hands near the screw can lead to severe injuries.

It is also important to prepare clean rags to remove old lubricant and dirt from the shaft. It is unacceptable to get abrasive particles into the glands when installing a new screw. If you are planning a replacement in the field, store water in advance to wash the knot from sand and silt.

Dismantling of the old propeller

The removal process begins with the removal of the protective cap, if it is provided by the design of your motor. Yamaha or MercuryAnd underneath, you'll see a locking pin or pin that locks the screw from spontaneous unwinding, and it's a disposable element, so when you dismantle it, you often have to cut it off or drill it out if it's rusted.

Once you remove the stopper, the most important thing is to unscrew the nut. screw-pinIt needs to be inserted into one of the holes on the screw hub and pushed into the stationary part of the gearbox, which will create the necessary resistance. With a sharp but controlled counterclockwise jerk, pull the nut out of place.

Procedure for dismantling:
Remove the locking pin/splint.
Place a hold in the screw hole.
3. Put the key in the gearbox body.
4. Strive the nut counterclockwise.

Often the nut gets stuck due to electrochemical corrosion, which is characteristic of aluminum alloys in salt water, in which case it is recommended to treat the connection with penetrating lubricant (such as WD-40) and wait 10-15 minutes. Do not apply excessive force immediately so as not to break the thread on the shaft, the restoration of which will be very expensive.

When the nut is unscrewed, carefully remove the puck and the screw itself. Pay attention to the state of the persistent puck and bushing. If there are deep furrows or bullies on them, they also need to be replaced, as they ensure proper centering and transmission of traction.

Diagnostics and selection of a new screw

Before you put a new part in, you need to understand why the previous one failed, and if the screw is just worn out over time, that's OK. But if you see chips on the edges, cracks or deformation of the blades, it's a signal of misuse or mismatched. screw-stepRocks and concrete piers are the main cause of breakdowns.

Choosing a new propeller is a balance between thrust and speed. Smaller pitch propellers allow faster speed and better pulling of a heavy boat, but lower top speed. Conversely, high pitch propellers increase speed but require a more powerful motor to go into operating mode. Wrong choice can lead to engine operation in overheating or vice versa, to undercoolness, which is equally harmful.

Type of screw	Materials	Application	Features
aluminum	Aluminum alloy	Standard, rental, fishing	Cheap, bends on impact, saves gearbox
Stainless steel	316L steel	Speedboats, heavy boats	Strong, holds the step, but passes the blow to the shaft
Composite	Carbon fibreglass	Tuning, specific tasks	Light, not rusting, roads in repair
Black Max	Toughened aluminum	Rental, rental, difficult conditions	High strength, average price

When buying, pay attention to the markings on the hub, which indicate the diameter and pitch (for example, 13x19).Suzuki, Tohatsu, Honda) the number of slats and their profile may differ, so a “example” is required before purchase.

What's a slip hub?

The Slip hub is a gearbox protection mechanism, and inside a rubber or polyurethane hub, the screw sits on the sleeves. When hit hard, the sleeve slips, preventing the gears of the gearbox or the engine crankshaft from breaking, and it's a consumable that requires periodic replacement.

Installation and centering of a new screw

Installation of the new screw begins with a thorough cleaning of the propeller shaft. Remove all the remnants of the old lubricant, rust and dirt. The shaft should be perfectly smooth. graphite-lubricant Or a special corrosion-resistant compound on the shaft and slits, which will prevent swelling and facilitate future replacement.

Put a hard puck (if it's separate) and the screw on the shaft. Make sure the slits match and the screw sits down to the end without skewing. If the screw is hard to put on, don't hammer it with a hammer, it can damage the hub. Easy swaying and lubrication usually help. Then set the conical puck and get the nut by hand.

• 🧼 Carefully clean the shaft of sand and old lubricant.
• 🛢️ Apply fresh graphite grease to the slats.
• 🔄 Make sure the screw sits tight and without backlash.
• 🔩 Set the nut with a new locking element.

Now you have to tighten the nut. It's critical to observe the puffing moment in your motor manual. If you don't tighten it, it will cause the screw to hang around, break the slats, and eventually fly off. Excessive puffing can warp the shaft or damage the thread. Use the dynamometer key for accuracy.

⚠️ Warning: Never use nuts from other motors or "picked" by thread. The thread pitch and cone angle can vary by fractions of a millimeter, leading to a jamming shaft on the water.

Pulling the nut and final fixation

The final step is to ensure that the nut is firmly fixed. Once the nut is tightened with the required force, you need to install a locking mechanism. In most modern motors, this is a pin that is hammered through the hole in the nut and shaft. In older models, you can use a splint that passes through the nut and the tail of the shaft.

If you use a pin, hit it to the point, but do not overdo it to not break the nut. If the pin does not come in, slightly twist the screw (either way, but not more than 10-15 degrees) so that the holes match. After installing the ends of the pin, it is recommended to open or open, so that it does not fall out from the vibration.

For engines that use splints, the procedure is similar, but it is important to use a new splint of the correct diameter. Reuse of old splints is prohibited, since the metal loses its elasticity and can burst. After installing the splint, put on a protective cap if it is provided by the design, and lock it.

Common mistakes when replacing the screw

One of the most common mistakes is ignoring the state of the persistent washer, and many aquatic motorists put a new screw on an old, worn washer, which causes the screw to not fully sit down, forming a gap, and as a result, the screw begins to "gnaw" the gearbox body, which leads to expensive repairs.

Another mistake is to use the wrong lubricant: the lithium lubricant or solidol in seawater is quickly washed out, leaving the shaft unprotected, use only special water-resistant lubricants for lower units, which have adhesion and do not dissolve in water.

And there's also a lot of this "twisting" error, and in order to lock the screw firmly, the owners build the key with the pipe, and that's the direct path to the shaft thread that's broken, and remember, it's not the tightening force of the screw that captures the screw, but the cone connection and the lock pin.

Can I use a propeller from another motor of the same power?

Only if the number of slits, the diameter of the shaft and the pitch of the nut carving match, even if the horsepower of different brands is the same.Yamaha vs Honda) these parameters are often different: Installation of an incompatible screw will lead to the destruction of the hub.

How often should you change the lubricant on the screw shaft?

If you are operating a boat in salt water, do a preventive lubrication at least once a month or after each trip to sea to prevent corrosion.

What to do if the thread on the screw nut is broken?

You can't operate the engine. You need to replace the nut. If the thread on the shaft itself is damaged, you need to disassemble the gearbox and replace the propeller shaft, which is a complex service procedure.

Why is the new screw whistled at high speeds?

A whistle can indicate cavitation due to too much pitch for a given motor, or damage to the edges of the blade, and it can also be the wrong installation of a persistent washer, creating turbulence.