I had engagement problems on the SD50 drive.
When selecting fwd, it would sometimes not engage immediately, and the throttle/gear selector had to be munipulated ("Blipped") a couple of times untill the drive engaged. Also with gear selector in fwd (Engine NOT running!) and manually turning the propeller
, the propeller
rotated about 1/2 revolution with a "spongy" feel before the drive engaged.
Checked cable adjustment on both Selector as well as gear & throttle lever assembly.
Also checked gear selector adjustment and shimming according to Yanmar manual.
Discovered that there was a lot of vertical up/down free-play on the upper vertical shaft, which was more than what the up/down rotation of the cone selector could accomodate to ensure engagement between the cone and the cup. The cone selector would dis-engage before the cone has mated sufficient with the cone cup to ensure positive drive. This partial engagement went unnoticed at low engine
rpm/load, and the propeller would turn but not exert the full thrust.
The cone clutch and cup design eliminates slippage under load due to the helical spline on the vertical shaft and cone. The higher the load on the propeller, the tighter the grip between the cone and the cup. This however can only happen if there is good initial grip between the cone and the clutch upon selecting drive before the cone selector dis-engages.
The cone selector partially dis-engages (retracts) in the fully engaged position to prevent wear between the selector surfaces and the cone selector groove!
This is more than likely the original cause of the SD50 cone clutch slippage problems.
If the drive is allowed to operate with the cone in this (unnoticed partially or lightly engaged) situation, it WILL lead to cone wear. This is especially true in light motoring/motor sailing.
We fixed our engagement problem before it developed into a slippage situation, with the resulting cone clutch replacement and associated shimming problems.
The way we went about was to measure and replace the Trust Washers, Collar and Nut with the correct thickness Thrust washers to achieve the desired free play.
The Thrust Washers are prone to wear, and the problem may re-appear.
We are however in the process of developing an improved installation
utilising Thrust Roller Bearings and reworked Collar and Nut to replace the Yanmar Thrust Washers etc.
uses the Thrust Bearings in their large capacity drives, and they do not have the problems that we experience with the Yanmar SD50.
NOTE; I had a VOLVO drive with Thrust Bearings in my previous boat, and NEVER had to re-adjust due to wear!