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I am dealing to buy 2 x Cummins 6 BTA 260 hp completely recon and with warranty for 2 years. (At a very good price ... about 3.000US$, both) The advise I really need is : what gearbox and what size of propeller should I mount? The struts and all are original B31 and I go to keep like that. I go to mount a 1 3/8 (35mm)shaft (Aquamet) that they say is more or less equivalent to 50 mm SS. I have from the old engines(Cummins V8-185) 2 x gearbox B&W 72C 1.51:1 but I don't know if it suits.
Thanks

Bruce will give you the best advice but moat have a 1.5:1 transmission and have wheels of about 20X24. I have 210's and kept the 1 3/8" shafts. Don't know about the 250-260's as to whether 1 1/2's are necessary. Walter

walterk wrote:Bruce will give you the best advice but moat have a 1.5:1 transmission and have wheels of about 20X24. I have 210's and kept the 1 3/8" shafts. Don't know about the 250-260's as to whether 1 1/2's are necessary. Walter

Tks Walter, if 1.5:1 is good then its very nice (less expenses) and the propeller you mean 20 diameter and 24 pitch , right ? About the shaft I am safe because they say that this Aquamet thing of 1 3/8 is the same as if you have a 1 1/2 of another type on what corresponds to torsion and things like that.
Thanks again

Luis-I think Uncle Vic has the same engines that you are putting in. His is a flybridge cruiser and I am pretty sure that his wheels are three blade 20" diameter 24" pitch. I don't think he has any cup in them, but drop him a line and I'm sure he'll give you the exact specs he's using.

Walter is right on the gear ratio due to the lower rpm.

However the BW velvet drive gears will not work they won't hold up.

You'll need twin disc or ZF gears.

If I was doing the job, I would use 1 -1/2 shafts but have seen others use 1-3/8.

Bruce wrote:Walter is right on the gear ratio due to the lower rpm.

However the BW velvet drive gears will not work they won't hold up.

You'll need twin disc or ZF gears.

If I was doing the job, I would use 1 -1/2 shafts but have seen others use 1-3/8.

Thanks Bruce, in another post I speak with UV and Walter about those Cummins 6BTA 260 but don't know about the B&W. So I must find other gearboxes, do you know exactly what could be better? I intend to keep
1 3/8 shaft Aquamet avoiding changing the struts and all that but I also come to a question based on UV : 21/22 propeller is ok (I think) but 3 or 4 blades? What you put?
Thanks again

he recommended the Hurth ZFgears not sure what exact model but i know they're 63a is good for gas bigblocks so it might be good for you're diesel.

ZF 220 like Vics got should be easy to find.

I prefer to use the 63a on higher rpm diesels in that hp range. It would probably work, but I never take a chance with a customers wallet.

I've seen too many of that series gears behind Cummins come apart 300 hours into service life.

What props I use depends on the customers budget.

To be honest on the 31 its so light that a properly done and balanced drive line is good with either a 3 or 4 blade. 3 is gonna be cheaper.

3 cavitate easier on hard reversing and can produce one hell of a racket.

The ZF220A is definately a good choice. If your looking for used or surplus gears...the Twin Disc MG 502A, MG 5010A, (MG 5050A is a bit over kill) but all would work fine. I've always heard good stuff about the ZF220 but personally I like the steel case on the TD gears.

And I agree, ditch the Borg Warners for a 6B Cummins. Not enough guts and no down angle. STAY away from the little BW with the down angle. I don't recall the model number but they were junk and not in production very long.

Thanks a lot to all of you. With your advices now I know what to look for. Thanks again