HANDBAG
As already alluded to, depends on amount of torque pulled.
Most airframes have at least three limitations.
Take off power - up to 5 minutes at approximately 5 - 10% over 100% power.
Max continuous.
And transient as stipulated in the POH.
The engine itself has torque limitations but I think you would have overspeed or overtemp problems prior to reaching it.
RIFFRAFF
Were did you learn your helicopter maintenance theory?
It all sounds the opposite to what I was taught.
Torque limits generally pertain to the airframe NOT the engine, it has to be a massive over-torque before engine maintenance has to be carried out.
Reverse flow engines are used as it makes the engine shorter in length.
Cheers
BH