Assuming the assembly was done properly, does this happen very often ? does HP have anything to do with it?

unit was rebuilt about 20 hours ago,

I have done a bunch of Imco lowers and never had a nut come loose. You are supposed to use red loctite on it and torque to 125 ft lbs. Was there Loctite on the threads.

I don't see any signs of loctite, I was able to remove the nut with my fingers.

That sucks.. Did the gears get destroyed?

I don't have it all the way apart yet. The gears show some wear. None of the lock tabs were bent out into the retainer, the prop shaft had play in it and has aluminum stuck to it. The more I see the more I beleive it was just a poor rebuild.

That's what it sounds like unfortunately. As Vinny said, there is supposed to be red Loctite on the nut. I drown them in Loctite and I have never heard of one coming loose before.....not just mine, but anyone's. I feel for ya.
Eddie

I run a lot of HP, but could this type of workmanship contribute to my lower gear loss, sometimes in as little as 4 hours. A couple of times just towing skiers and tubers?

it would seem to me that if you are blowing up lowers every 4 hours and using the boat recreationally then continuing to beat THAT particular horse is really short sighted. you need much bigger and much tougher drives.

i couldn't live with ANYTHING i had to rebuild every 4 hours.

How much hp? Things that dictate the life of a drive in order, at least the way I see it.

1- How the drive was set up
2- Driving habits
3- Horse Power

4 hours is nuts. I recently did a B-Max lower ( same as an XR )for someone. He is running upwards of 1200 hp. Not sure how many hours he put on it, but he put it on in May and ran it all year.