SigmaDrive Support

SigmaDrive propeller shaft couplings are a simple and effective solution to noise, vibration and engine misalignment.  This page will be updated regularly to provide the best resource for installation, operation and removal of the SigmaDrive series of couplings.  For direct help please contact King Propulsion direct on (757) 962-9219

How Do I Install SigmaDrive?

Each SigmaDrive model has different requirements for installation, below is an overview taken from the SD55 installation to serve as an illustrative guide.  Each SigmaDrive ships with a complete set of instructions and these should be followed.

To install you need to decide if you will haul the boat and work on the hard or work afloat.  Both are viable options for SigmaDrive and present different challenges.  Primarily the main decision is on the shaft stuffing box / shaft log.  If the vessel has a conventional shaft log that can be tightened to control the drip of water needed to lubricate it, this is a good candidate for in water installation.  If the vessel has a PSS dripless coupling, great care, attention and expertise is needed to back off the ceramic disk / seal and not flood the engine compartment.  It its possible and has been done countless times, but if you are unsure, it would be better to do the install on the hard where there is no issue with breaking the seal of the PSS.  The hard also allows the propeller overhang to be observed and reset after the installation.

  1. To install, first carefully clean the gearbox output flange and shaft contact surfaces. Fit the supplied high tensile studs into the corresponding tapped holes to match the gearbox output flange. Lock the studs using the loctite 638 supplied.
  2. Remove the river taper lock collar from the SigmaDrive unit leaving the body only
  3. Place the SigmaDrive body .onto the gearbox flange. the Fit the Nyloc nuts  to the high tensile studs and tighten firmly to the specified torque.
  4. Apply a later of anti seize compound (supplied) on the surface of the tapered collar that mates with the SigmaDrive housing lock making sure that the surface between the taper and central sphere is well covered, this will aid removal.
  5. Slide the clamping unit onto the propeller shaft to the minimum depth required. This is the most difficult part of the procedure as the collar is an interference fit.  The collar may need to be opened with a wedge (screwdriver etc) in order to start it on the shaft.  It will not simply slide onto the shaft and this is one of the main cases for hauling the boat – manipulating the shaft during this step.
  6. Once the taper collar is on the shaft, insert the clamping unit into the central sphere and tighten the  taper locking bolts  gently using an Allen key in a crossed sequence.
  7. Tighten the taper locking bolts  in the sequence indicated at least 5 times by hand.
  8. Tighten the taper locking bolts in the required sequence with a torque wrench in 3 increments. Do not exceed the maximum torque as the SigmaDrive can be difficult to remove if overtightened.
  9. Note that the shaft will be drawn up into the clamp by as much as 1/4 inch. Proceed with normal alignment and fixing methods with propeller shaft and transmission, taking care not to exceed the maximum working angle when centering Sigmadrive to transmission output flange.
  10. The shaft should be aligned when SigmaDrive is installed.  this can either be done using the old hard coupling or using the supplied wedges to isolate the gimbal system of the Sigmadrive making it effectively a hard coupling.  The unit can then be released from the output flange and the alignment proceed as normal with feeler gauges

Initial Startup

Before starting the engine, rotate the shaft manually by hand and check that it rotates easily in both directions. Check and if necessary reduce working angle. It is preferable to make sure that the shaft is aligned to start with as the maximum installation angle should not exceed 3 degrees. The smaller the angle the longer the lifespan of the SigmaDrive will be. The angle can be measured using a bevel gauge and should not exceed our recommendation. After initial sea trials the engine can be adjusted to reach the perfect working angle of alignment, this will be necessary especially if there is any irregular movement on the coupling, when in operation.

The SigmaDrive unit is packed with special high temperature grease. During initial operation it is very likely for the component to expel grease. The operating temperature, in some cases, can make the coupling run a little hot making the grease more fluid. We recommend cleaning the excess grease from the coupling, from time to time, using a cloth. Ensure the vessel is stationary and the engine is switched off, preferably at the dock, when following this procedure. Please also check the temperature of the couplings as they may still be near to running temperature after initial motoring trials, this can be as much as 90 degrees.

Run installation to bring engine up to working temperature and re-check torque settings on the gearbox flange nuts and also the shaft taperlock.


The Sigmadrive is extremely low maintenance and does not require re-greasing when aligned. The unit is pre-filled with grease and uses an o-ring system to keep it sealed.  It is recommended at each major haul out when cutless bearings or engine repair work is being performed to re-grease the unit, typically a 5 year interval or greater. Periodically check mounting bolts and nuts for tightness and overall condition.