I'm blowing an upper gear set every 300-900 hrs on my Bravo 2xes behind Yanmar 6lp 315 diesels. I've gone the "upgrade" route and have had about the same success as with new factory drives. Some go a while, some don't. It sounds like my best options are Imco's SCX or BMAX upper. I haven't had a lower failure in a while, so I think I can stick with those for a while. The Imco requires a new helmet, so I have to change my transom assemblies to HPs. Any reason to go one way or another, or not to? I've also heard about XZ drives. I was told not to use XRs because diesels don't like straight cut gears, or vice versa. Where does the XZ fit in, and would that be an option? Thanks.

An XZ is a X upper( what you currently run) with a XR ( 1.25" prop shaft) lower....this won't fix you issue...I would focus on ditching the merc upper

Go with the IMCO SCX! Between the B-Max and the Imco, the IMCO is the better choice.

I would also call,, Max Machine in Lake Havasu, AZ. , the build HP. drives for most any application, great guys.

I don't understand why a Diesel doesn't like straight cut gears, XR is good for about 600 HP.

Have you thought about gear ratio and prop change. Is it a heavy boat

http://motoresdelpacifico.com/wp-con...rgas/ZT370.pdf.

I just spoke to Max Machine. I might try the upper parts kit before I go any further. They are pretty confident that their upgrades will strengthen things up enough to keep my drives alive. I'm still not sure why xr gears won't work, but I have heard that they will slow me down. How would a gear ratio change help? They uppers are 27/29. From what I've seen, the other option is 27/32 and that would have smaller teeth on the driven, correct? Thanks again for the input.

If you're looking for longevity, XR gears aren't the answer

XZ are helical cut gears - not as strong as the XR straight cut gear.

If you are getting a median of 600 hours out of ANY Bravo drive, that's actually pretty good!!
What kind of hours do you put on in a month and/or a year?
What kind of RPMs are we talking?
How much weight are you pushing?
What is your maintenance schedule? (fluid changes)
Are you cooling the drives?
Do you have drive temperature fluid gauges to monitor their health?

If you have a high usage fleet and or business fishing boat, I don't think Bravos are your best bet for long term.
I think a Bravo to Arneson conversion may be in order.