ZF SD10 with wrong handed propeller

[danielb]

Hi All,
I own a 28ft yacht with a one-off marinized Briggs and Stratton DM950D mated to a SD10 purchased from a Nanni dealer. The PO had the installation done.

So a while back I found out my prop is wrong 'handed' (its RH or CW) for my SD10. Direction 'A' on the saildrive dimensions schematics, apparently for forward, is shown as LH/CCW.
Since the prop is now bust (after maybe 10 years service) I was considering replacement with the correct handing.

In the SD10 owners manual it says gear 'A' makes prop spin opposite direction to engine rotation. 'B' gear same direction.
There nothing I can find that states the preferred input rotation direction (ie engine rotation).

My engine output shaft turns CCW (looking towards block). So in gear 'A' for forward, based on the above, the prop shaft should be turning CW.
So it seems to me with my current setup, its actually using the 'correct' A gear, but everything is turning opposite direction...

To further confuse things,
A ZF support person mentioned that "the drive has to pass through an extra idler gear or intermediate shaft for the B position", hence A should always be used for forward. I suspect this might be true for a conventional box, not a saildrive.
I don't see any such part, or reason for one, when I examined the exploded drawings in the parts or service manual. The shift mechanism appears to work by engaging via clutch one of two identical pinion gears on opposite sides of the ring gear. The assembly looks symetrical, even the bearings look same size at each end.

Further to this a paragraph in the service manual states on reassembly "Align the actuating parts in relation to the engine rotation." To me this reads that the SD can be driven CW or CCW. But this conflicts with either the propeller direction or the use of A vs B gear for forward.

Lastly, according to service manual photos, the gears are all helical cut. However the detailed parts list drawings show them straight cut. If helical, doesn't this mean they run better in one direction than the other?

So I have some conflicting info, and I guess my question is, what's more important:
1) 'Correct' CCW rotation direction at the prop shaft, (using the 'B' gear due to engine input also being CCW).
2) Use 'A' gear, resulting in CW rotation at prop shaft.

[Compass790]

My GUESS would be that if forward & reverse mechanisms are identical it should not matter.
We are running our Kanzaki gearbox using reverse as forward as I KNOW the gears are the same size & ratio & we got a free wrong handed prop. It spins one extra shaft in our case which would result in small parasitic losses but not enuff to worry about.
But better to take advice from someone who has stripped down an SD10

[Ostinato]

Call or email ZF in Italy. They should be able to help though I had mixed responsiveness from them in the past. If I can find the email address of their VP for aftermarket service I’ll pm you.

[FPNC]

The ZF SD10 does not use a counter gear for reversing shaft rotation. Reduction ratio is the same in both the A and B position. You can use either a left or right hand rotation propeller. Neither choice will have any effect on the operation of the transmission.

[crackerEV]

Originally Posted by Compass790

My GUESS would be that if forward & reverse mechanisms are identical it should not matter.
We are running our Kanzaki gearbox using reverse as forward as I KNOW the gears are the same size & ratio & we got a free wrong handed prop. It spins one extra shaft in our case which would result in small parasitic losses but not enuff to worry about.
But better to take advice from someone who has stripped down an SD10

The large Kanzakis we had previously, could not be operated reversed for the same amount of warranted time between overhauls. I asked them for an overhaul time and they refused to provide.