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Presently running a 6BTA 250hp cummins in a workboat. It has a velvet drive 2.5:1 gear. I’m looking to upgrade the gear to something more robust. I’ve seen a few MG506/507s around. I’ve been advised that these might be a good candidate for replacement. Most likely the boat will need a new shaft to make up the different case measurements. I am also thinking of changing the gear ratio to 2:1 to bring a new prop to 23″ square ish….
In the future…5 years??? I will be repowering with a higher hp cummins QSB (480 or maybe max keel cooled B, which I think is in the low 400s). Should I make the purchase of the gear now….that can handle the increased hp from the expected repower? What is out there for coaxial gears ZF and TD that anyone could recommend.
Thanks
D
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MG 506 & MG 507
The MG506 & MG507 are both “good ol” gears, but both have been out of production for over 20 yrs now.. Lots on them still around and both are easy to rebuild as gears go as long as the gear is in “still working condition” and is not a total rust bucket.
With that said, the MG507 would not be an easy gear to adapt to any B series Cummins ( clearance issues with the turbo and possibly other things).
From experience, the MG506 with a proper, & fresh rebuild, and installed right would be an OK gear for any B up to 350-400 HP at 3000++ RPM . The 506 does not handle the lower RPM torque of the 6CTA 8.3.
I like both gears a lot, but you need to understand their limitations…………………. In many ways this applies–“They just don’t build them like they used to”
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