K4 Feathering & Auto-Rotation:
First check the blades are all free on the axis and the reverse rollers free to rotate.
They are in affect forced through 180° every time a reverse action is undertaken so are mechanically kept clean if you will.
With a hydraulic gearbox you will not be able to lock the unit into gear to prevent auto rotation.
If the unit is rotasting when sailing is possible there is too little pre-tension on the internal torsion spring the spring. This may well have been adjusted previously.
Reducing spring tension can assist with easier reverse engagement but reducing it too far the impacts the feathering function.
There is a very detailed write up - search for 'K4 Spring Tension'.
- In a nut shell - the spring tension should be just sufficient to ensure the shaft rotates in parallel when you rotate the prop blades slowly by hand with an unlocked shaft In the direction that increases spring tension. If rotation winds up the spring before the shaft moves - it has the effect of reducing the over centre capability of the blades which accommodates the shaft angles of your installation – the result being auto rotation. In effect the blades over centre position reduces as the reverse roller forces the blade on one side of the unit to a position where it will start to generate lift from the streamline it “ sees “ entering the propeller. Note this is not the shaft angle but the angle the blade would “ see “ from the incoming water when sailing.
Obviously any damage or break of the spring will prevent further in this could be a corrosion issue but the unit would need to be examined internally to determine this if the blades are not being returned.
It would appear from your video that the spring is fully intact ao we are simply talking about an initial position adjustment.
You should be able to test this by seeing if when you rotate the blade assembly slowly spring tension is sufficient to immediately move the shaft which indicates the unit is not winding up and starting to partially engage reverse so providing lift on the blade on one side of the unit. Once this occurs - the unit rotates and the situation is repeated - hence auto rotation
In a nutshell the steps to correct would be as follows:
- Make sure the unit is fully greased first - btoh fore and aft in the boss plus the 4 x blades as per the video on our web site
- Mark with an indelible pen the collar that tails the spring which is the first component aft of the nose is located relative to the blade carrier casting.
- Loosen the M8 set screw which provides an additional level of locking security opposite the M8 Screw which spans the slot in the collar
- Loosen the M8 Cap screw that spans the slot and by tapping the collar in either direction - you can tighten or loose in the spring tension. The website will confirm the direction but basically to increase tension you want to increase the force required to initiate movement of the blade assembly so moving the blade assembly slowly immediately moves the shaft.
- When the new level of tension has been set, you basically repeat the process by tightening the M8 Cap Screw across the slot which pulls the collar down onto the boss and prevent any further rotation.
- You then re-tighten the backup M8 set screw located 180° opposite as the additional locking feature.
NB: You cannot increase spring tension past the point where the boss no longer fully rotates 100º and ends up rotating the shaft with the spring rather than the internal dog which should engage with a distinct click as the two metal surfaces come into contact
It is important you follow the instructions for feathering which you may well be doing, but to summarise:
- Reduce engine speed to idle for 30 secs while still in gear and sailing
- Move the gear shift to neutral