I had a problem with a SD50
drive (1000Hrs) where the drive would only partially engage when selecting Fwd. The propeller
would turn, but would not exert the full thrust. The throttle had to be "Blipped" (revved up) a couple of times while watching the propwash until the drive engaged.
I checked both the control cables
for the correct stroke length, as well as the selector up-down movement and selector (centre bolt) shimming.
When rotating the propeller
by hand with the gear
selector in Fwd, the propeller would rotate approx 1/2 a turn before engaging. There was also a "spongy" feel when it engaged, compared to the drive on the other engine
(catamaran) which immediately engaged solidly when rotated manually.
If the drive is allowed to operate in this partially engaged situation, it would lead to rapid wear between the Cone Clutch
and Cone Cup mating surfaces. This would result in a damaged/ruined "Slipping" drive and require the notorious and expensive Cone Clutch
Assembly replacement, along with the associated installation
and shimming problems.
The design of the helical splined Cone and Shaft assembly prevents any slippage between the Cone and Cup giving more grip with higher load exerted by the propeller. This is a fool-proof system, on condition that initial full contact is made between the Cone and Cup before load is applied by the propeller, as well as BEFORE THE CONE SELECTOR RETRACTS.
The Cone Selector has limited up-down stroke, and has a retract function at the end of the Up or Down stroke. The reason for this is to move the tapered surface of the Selector away from the tapered Groove in the Cone to prevent wear between the Selector and The Cone during operation.
The stroke of the Cone Selector is not sufficient to compensate for the wear that develops in the Thrust Washers, Collar, Split Ring and Top Nut, resulting in the Cone Selector retracting away from the Cone groove before the Cone has engaged fully with the Cone Cup.
I replaced the lower Collar, top Nut and Thrust Washers, making sure that there is limited vertical free play on the Cone Shaft.
The Trust Washers, Collar and Top Nut are prone to wear, and has to be inspected regularly for wear.
PROBLEM SOLVED- I am however in the process of developing a Thrust Bearing, revised Collar and Top Nut assembly which will eliminate wear. VOLVO
has been using Thrust Bearings for years! My previous boat has a VOVO drive with Thrust Bearings, and is still going strong after 14Years!