Torsion of the outboard motor propeller: how to recognize, eliminate and prevent

The torsion of the outboard motor propeller is one of the most unpleasant and unexpected failures that any boating can encounter. Most often, the problem occurs when a collision with an underwater obstacle, a sudden change in load or factory defect. The consequences range from a slight imbalance to the complete destruction of the gearbox, which makes the motor unusable. screw-tower at an early stage, what measures to take immediately after the incident and how to repair yourself - without contacting the service center.

The problem is that its symptoms are often disguised as other malfunctions, such as vibration from blade imbalances, wear and tear of bearings, or even problems with the fuel system. cavitation It's a phenomenon where the screw grabs air instead of water, but the mechanism of damage is fundamentally different. process-physicsso that you can clearly distinguish the torsion from other breakdowns, as well as give step-by-step instructions for diagnosing and troubleshooting the malfunction.

The article will be useful for both beginners and experienced owners of outboard motors brands Yamaha, Mercury, Honda, Tohatsu And we're going to focus on prevention, because it's always cheaper to prevent torsion than to repair the effects.

What is a screw torsion and why does it happen?

The screw twist is the deformation or displacement of the blades relative to the axis of rotationUnlike the normal bending of the blade (which is also dangerous), the torsion affects the torsion. screw-hole It can damage the gearbox shaft, and it's for a number of reasons.

• 🪨 Impact on underwater obstacle Even a minor collision at high speed can deform the hub.
• 🌀 Dramatic load change - for example, when the screw suddenly "grabs" air when entering the crest of the wave or when a sharp acceleration.
• ⚙️ Wear or defect of the gearboxIf gear bearings are worn out, the screw can "walk" and deform even during normal operation.
• 🔧 Incorrect installation of the screwA tightened or insufficiently tightened nut of the hub leads to backlash and subsequent torsion.

The most dangerous scenario is when the torsion occurs high-speedIn this case, the impact energy is transmitted to the gearshaft, which can cause the gears to collapse, or even the motor body. Mercury 15-30 hp The plastic gear of the gear reducer often suffers, and Yamaha F20–F50 - shaft bearings.

Interesting fact: the screw torsion often occurs on aluminum-boatThis is because aluminum is more powerful at conveying the impact to the engine, whereas an inflatable boat is partially cushioning the load.

Signs of screw torsion: how to recognize the problem?

The torsion of the screw rarely occurs instantly - it is usually preceded by side-symptomsHere are the key signs to look out for:

• ⚠️ Vibration on the hull of the boatIf you haven't had one before, it's an excuse to look at the propeller.
• 🔊 Uncharacteristic noise from the gearbox: grinding, knocking or "crunch" when the screw is rotated.
• 📉 Maximum speed reduction This is because of the change in angle of attack of the blades.
• 🌀 Uneven rotation of the screwIf you look around and you notice that the blades are not rotating in the same plane, that's a sure sign of torsion.

For accurate diagnosis, perform the following test:

1. Lift the motor out of the water and turn on at idle speeds.
2. Carefully examine the path of rotation of the blades. Normally, all the blades should be in the same plane (their tips when rotating "paint" the perfect circle).
3. If at least one blade "goes" up or down - the screw is twisted.

⚠️ Attention: Don't confuse torsion with torsion. cavitationWhen cavitation occurs, the blades will have small shells, but the geometry of the screw will not change, and the torsion will always lead to deformation of the hub or blades.

Another way of testing. tactile:

1. Remove the propeller from the engine.
2. Place it on a flat surface (like glass).
3. Scroll the screw with your hand: if it "hits" or touches the surface, there is a torsion.

The consequences of torsion: what breaks in the engine?

If you ignore the torsion of the screw, the consequences can be critical - up to full-outHere's what's suffering in the first place:

Engine assembly	Nature of damage	Cost of repair (approximately)
Spin hub	Deformation, cracks, destruction of the rubber damper	from 1,500 RUB (replacement of the hub)
The gearbox shaft	Wearing of the slats, bending, destruction of bearings	from 5 000 RUB (shaft replacement + bearings)
gearbox	Chipped teeth, wear, destruction of plastic gears (Mercury)	from 8 000 RUB (set of gears + work)
The gearbox	Cracks, leakage, leaking oil	from 10 000 (replacement of the body or the entire gearbox)

Motors with particular vulnerability plastic-handle (for example, Mercury 9.9-15 hp or Tohatsu MFS15When you torsion the screw, the impact load is transferred to the gears, which simply crumble, in which case it costs 30-50% of the cost of the new engine.

Another danger. shaft-breakingIf the screw is twisted, it creates a beat that quickly disables the bearings. metal-shavingIf it's found, the engine needs to be disassembled immediately.

⚠️ Attention: On the engines with hydro-lift (for example, Honda BF20/30) torsion of the propeller may damage the trim-tilt system, resulting in leakage of hydraulic fluid and failure of the lifting mechanism.

What to do immediately after the screw is twisted?

If you feel a blow or notice signs of torsion, Follow these steps immediately:

1. Stop the engine. And turn off the ignition, and continuing to do so will exacerbate the damage.
2. Get the motor out of the water. And inspect the screw for visible deformities.
3. Try to turn the screw with your hand.If it's spinning with difficulty or it's getting stuck, the gearbox is already damaged.
4. Check the oil in the gearbox.If it has metal chips, you have to bring the engine to service.

If the screw is externally intact, but there is suspicion of torsion:

• 🔧 Take off the screw and look at the hub. Cracks or deformities are a reason to replace.
• 🛠️ Check the gearbox shaft for beat. You can use a clock-type indicator (if you have experience).
• 📏 Measure the gap between the blades and the anti-cavitation stove. If it's uneven, the screw is twisted.

Don't try to straighten the screw with a hammer or other improvised tools. Aluminum and stainless screws have a strict geometry, and any deformation will lead to imbalance. screw-up (if the design is collapsible).

Repair of the screw torsion: step-by-step instructions

If the diagnostics confirm a torsion, we'll start repairing it. hub-replacement (for collapsible screws) and screw-up (for indiscriminate).

Scenario 1: Hub replacement (for rubber damper screws)

Many screws (e.g., Mercury Black Max or Yamaha Saltwater Series II) have a removable hub with a rubber damper, which can be replaced without buying a new screw.

1. Remove the screw from the motor by unscrewing the hub nut (use) key Or the head with the extension.
2. Press the screw in the vise through soft pads (for example, rubber) so as not to damage the blades.
3. With a filmmaker or a screwdriver, squirt and remove the old hub. Be careful, there may be springs or balls inside!
4. Clean the seat of the old lubricant and install a new hub. sea-lubrication (for example, Yamalube Grease).
5. Tighten the hub nut with the force indicated in the motor manual (usually) 40-60 Nm.).

After replacing the hub, be sure to check the screw on the balancing stand. Even a slight imbalance will lead to vibration and accelerated wear of the gearbox.

Scenario 2: Complete rotor replacement

If the screw is indissoluble (e.g., Honda 3-blade aluminum or Tohatsu NSAIt's going to have to be replaced entirely. When you pick a new screw, consider:

• 📏 Screw pitch (It should be the same as recommended for your engine.)
• 🔄 Diameter and number of blades (e.g. 3-blade or 4-blade).
• 🛡️ MaterialsAluminum (cheaper but less durable) or stainless steel (more expensive but more durable).
• 🔧 Hub type: under your motor (e.g., under your motor) Splines 10 or Rubber Hub).

After installing the new screw:

1. Check the nut tightening of the hub (shortage or overtraction will lead to repeated torsion!).
2. Pour fresh oil into the gearbox (even if the old one looks normal).
3. Test the engine at idle and medium revs, listening to extraneous sounds.

⚠️ Attention: When replacing the propeller on the motors Mercury and Yamaha After 2010, check the status of the water-jet Its wear and tear can exacerbate cooling problems.

How do you pick up a screw in step?

The screw's pitch is measured in inches and indicates how far the screw will advance in one full turn. 11" It is suitable for motors 15-30 hp on light boats, and 13–15" - for heavy boats or engines 40+ hp Detailed tables of compatibility are in the manuals of manufacturers.

Torsion prevention: how to avoid the problem?

It's easier to prevent a screw from torsion than to eliminate it. 5 key rules of the ruleTo help you avoid the breakdown:

• 🗺️ Explore the waters.Before heading out on the water, check the depth maps and marks of other anglers (for example, in applications). Navionics or Fishbrain).
• 🚤 Keep up the speed limit. In shallow waters and overgrown areas, keep your speed at a minimum.
• 🔧 Check the screw fixing regularlyThe nut of the hub should be tightened with the correct force (see motor manual).
• 🛡️ Use protective devices:
  • 🛩️ Rubber-hoop screw (dampenses the punches).
  • 🛡️ Protective grid (Prevents the ingress of debris).
  • 📏 Depth sensor (helps avoid shallow water).
• 🔄 Get the gearbox to the TA.Change the oil every 100 hours or once a season (depending on the intensity of operation).

Pay special attention screw-selectionFor example, for shallow water, screws with footsteps and large-diameter They're less susceptible to torsion when hit. steel-rotor on rocky water bodies: they are stronger than aluminum, but when impacted, transfer all the energy to the gearbox.

If you often walk on unfamiliar water bodies, consider installing a water system. propeller-protectionsuch as Power Tilt (automatic lifting of the motor on impact) or Kick-Up These devices are expensive, but they pay off when you hit a major collision.

Frequent errors in repairing the screw torsion

Many water-engines try to save on repairs by making critical mistakes. don't under no circumstances:

• 🔨 Hammer-shootingEven if the screw is visually smoother, the internal stresses in the metal will lead to cracks.
• 🔧 Use of non-original hubsCheap Chinese counterparts often have inaccurate geometry, leading to imbalances.
• 🛢️ Savings on oil for the gearboxCheap mineral oils can't withstand the loads and lead to bullying on the gears.
• 📏 Incorrect selection of the screw stepToo much pressure increases the gearbox, and too little pressure causes a torsion at abrupt acceleration.
• ⚡ Ignoring vibrationIf after the repair there is still vibration, then the problem is not fixed (may bend the gearshaft).

A common mistake. eye-tighteningLike motors. Yamaha puff-up 50 Nm.eh Mercury — 40 Nm.Exceeding this value leads to deformation of the hub, and insufficient puff leads to backlash and torsion. dynamometer!

Another myth is that stainless-screw They're actually stronger than aluminum, but when you twist them, they put a lot of pressure on the gearbox. Mercury 9.9) it is better to use aluminum screws, which "soften" the impact.

FAQ: Answers to frequent questions

Can I drive with a twisted screw if the engine is still running?

Even if the engine is running, the twisted screw creates a spin. beatIt's a shaft that destroys gear bearings, and after 10 to 20 hours of this operation, you're going to have to repair not only the screw, but also the gearshaft, and you're going to have to replace the screw or the hub right away.

Which screw is less susceptible to torsion: aluminum or stainless?

Aluminum screws are softer and partially absorb the load when impacted, whereas stainless screws transfer it to the gearbox. However, aluminum screws wear out faster and require replacement every 2-3 seasons.

• For rocky water bodies, aluminum.
• For clean water and high speeds, stainless steel.

What if there is still vibration after the replacement?

Vibration after replacement of the screw can be caused by:

1. Incorrect balancing of the new screw (you need to balance on the stand).
2. The bent shaft of the gearbox (requires a replacement shaft).
3. Worn bearings of the gearbox (you need to disassemble and inspect).

Start by checking the balance, then inspect the shaft for the beat.

How much does it cost to repair the gearbox after the screw is twisted?

The cost depends on the model of the engine and the degree of damage:

• Replacement of the screw hub - from 1 500 ₽.
• Replacement of bearings of the shaft - from 5 000 ₽.
• Repair gear reducer - from 8 000 ₽.
• Replacement of the entire gearbox from 20 000 ₽ (for motors 15-30 hp.).

On premium motors (for example, Yamaha F150) repairs may be required in 50,000 and above.

Can I repair a twisted screw myself?

If the screw aluminum and the deformation is not strong, you can try to correct it on stand-up It's got to be a beat indicator, but it takes skills and equipment. Stainless screws They can't be repaired, they can only be replaced, and in most cases it's easier and cheaper to buy a new screw than to risk a second torsion.