After looking at it this weekend I found 1 tooth broke on a gear . I'm thinking when the tooth went through the gears it pushed the top cap up and pulled the threads. As you have said there is not much meat there so I will go with the heli coil's and stud's. Still not sure why it broke ? The drive has less than 50 hours on it. Thinking about going back to bravo 1's if I'm going to be braking drives it might as well be the cheap ones. Thanks again for your advise, Jeff

Jeff,
I have seen more of this problem than I want to. XR upper gear sets, one tooth broken off at the root of the gear. Happening more and more. Used to be we could run 1100hp thru the gears and they would just flake away. Now a perfectly good gear just snaps a tooth off.
My .02 is that Merc has another supplier and quality is not an issue. If people want to run big power (over 550hp) then just opt for the new NXT / 525hp package. Of course you will need to order the new boat with that package also..
I have been talking to someone that says he can make better gears, just dont have the $250k to try a set.
How much HP and Torque? How much does the boat weigh? You may be right. The Helical cut gears may be better at this point. I have always said that if you dont have enough power to knock the teeth off the Helical's, then run them. You still have the problem of the lower gears falling apart.
My sugestion is go with the IMCO SCX. It has bigger gears and no problems so far. But the lower unit is larger, and it will slow down the boat. So add more power if you can (add boost?) or be ready to replace the weak link often..

Dick

The motors dyno'd at 742 hp and 830 ft-lbs and I'm turning 31 pitch 4 blade merc prop's . The boat ran for 200 hours on bravo 1's when it started to twist the prop shaft's . So the xr's were put on with imco lowers and now this sh!t . At least I have all winter to fix it .

Jeff,
You might want to think about going back to the helical cut gears in the upper.. the XZ gears will fit your XR upper case, properly setup. They are the weaker setup, but with the XR gears wearing out and falling apart, in your case the XZ gears may suit your maintenance schedule expectations. I know a lot of guys that think along these lines and their drives hold up pretty good. They know they are breakable, so driven with caution they seem to last. Not forever, but acceptable time frames for their expectations.
Dick

Looks like I'm going to fix what I have . Just burns my but when you spend the money on the so called good parts and this happens. Thanks again for the advice . Jeff