Thanks Scott, i did think that was way too tight. The rear shaft nut is only 120nm !
I've managed to get a 2nd hand hub of ebay for £20 so will do them up to 60nm.
http://www.600riders.com/forum/fz6-technical/12290-rear-sprocket-nut-problem.html
I ended up using 45 ft/lb for the torque of the nuts.
Snipped.....
Hub is used on many Yam's R6, R1, spec is correct as the tension from the fastener is supposed to be great enough to stop rotation of the sprocket under load. The studs sticking out are not the key ingredient in stoping rotation or they would have used dowel pins. They didn't. The clamping force created by applying the suggested torque is there for a reason. I mean would you torque a rod bolt 50% less than spec because one stripped? NO! You'd fix the problem!
That said, Get as close to OEM torque w/out going over with a value you think is adequate. I'd shoot for no less than 60ft/lbs myself.
And you will probably find that you will strip a stud. It's about 12MM diameter for the stud. You actually think that it's correct to tighten that steel nut/aluminum stud to 72 ft/lbs. when the manual specifies to tighten the steel 18MM front sprocket nut to only 65 ft/lbs.?
The thing to keep in mind for an assembly like this is that the studs themselves do not transmit power between the sprocket and wheel hub. They just provide a clamping force between the two. The friction between the sprocket and wheel hub is what keeps the two parts from moving against each other.
If the studs were transmitting the engine's power to the wheels directly, they wouldn't last very long at all, as the sprocket would hammer against the studs every time you got on or off the throttle.
And in the end, it's your bike and you're responsible for deciding what is safe.
Fred
I only torque my rear wheel up to about 90 or 100nM. Same with my car tyre nuts. No way I'd go that high on the sprocket carrier with it's much smaller stud size