Gearboxes

[twonahil]

We a B31 that we are installing Cummins QSB 5.9 230 HP at 2800RPM engines in and need to get a new set of gear boxes. Any recommendations on what gearboxes (ZF or twin disk) and what gear ratio (2.5:1, 2:1 or 1.5:1) and depending on gear ratio what props we should be running?

[Tony Meola]

Hopefully Bruce will chime in, but not sure if there is a big difference between the 230 and old 250. The old 250/270 used 1.5 to 1 ZF as the most common and spun a wheel from 20 to 21 inches with a pitch of around 20 to 23. A good prop guy can help you there.

[scot]

Twin Disc TD5050A 1.5:1
Cummins sold the 6BTA in commercial applications matched with the TD5050A for years. Heavy duty gear. It is going to cost you more than the ZF option, but it's made of steel, and can be fitted with a trolling valve if you choose.

IMHO it's about the best gear you could put behind the Cummins, but not the least expensive or the lightest.

[twonahil]

Tony/Scott,
Thank you for your help. It sounds like 1.5:1 is the way to go and both the MG-5050a and the ZF220A are the gearboxes we are having a hard time deciding between. We currently have a set of twin disk 502's that came with the engines that are 2:1 that when we took them to get serviced were going to cost almost as much to rebuild as it cost for a new set because they no longer carry parts for them.

[scot]

I don't think you can go wrong with either ZF220A or MG5050A. The TD will typically cost close to a $1000 more per unit and weighs 197 lbs. I think the ZF weighs around 110 lbs.

Good luck.