Dr. Alan

[Debra Lee]

We have a mission boat that we wish to use in Vanuatu for mission work. We recently purchased this boat. It has a Yanmar 3 QM 30 with a Kanzaki KH 18 gearbox at a 3 to 1 ratio. Problem very poor reverse gear selection. You need to push the lever right back to engage. Second we were supplied another gearbox from Sound Marine Diesel. This box was a 2.03 to 1. We went to the expense of having the "reconditioned" box fitted only to find no forward gear. The supplier SMD has concurred the clutch plates are slipping and it needs overhaul. Any clews on a replacement box or on the reason for the poor selection on reverse. I have replaced the selector and no change.

[Boracay]

Hi and welcome to the Cruisers Forum.

I did a quick search on your engine/gearbox and found this thread, which pretty well sums up your problem.

You'll need to verify the information in the above link, but if it is correct you could find it very difficult to fix, rebuild or even to replace your gearbox.

You don't say what sort of boat you have, but with the heavier yachts that many members on this Forum have some of the smaller marine gearboxes have not given good service when operated continuously.

I don't have any great deal of gearbox experience. I specified a gearbox that had three times the required specification for my boat and have, so far, experienced no major problems.

I seem to recall a rumour that the smaller Twin Disk gearboxes are possibly a little more study as a replacement.

The procedure in the first link of sending the gearbox off to have the adapter plate accurately measured so it can be fitted to a new gearbox may be necessary.

I did not find any reference to the Kanzaki KH18 having a 3:1 ratio so I'd recommend that you check this before spending too much more time and money.

The time and money involved may be better invested in a new engine/transmission.