XUD TDT- Status = SELLING ALL THE BITS.

[Rippthrough]

It may well not be the torque that destroys it as such, but how low down that torque is.. bike engines rev to like 13k, you'll be getting max torque at like 2.2krpm in a 1.9 XUD

It'll be the shock loadings, and the torque pulses from a diesel (lets face it, they ain't up there on the list of smooth powerplants)
Shock is what kills gearboxes and shafts more than anything, that's why the gears we use in the buggy are over an inch wide even though they're made from decent stuff.
That's also why the drag bikes tend to strip the gearkit out and fit 3 really damned big gears instead of the stock 6.