Originally Posted by
rotorfun
When installing main rotor tie down, AFM for Bell 505 indicates rotating rotors in the opposite direction. Not sure why...
"Rotate main rotor blades in opposite direction of rotation until main rotor blades are aligned with tail boom."
The 505 rotor system is derived from the Long Ranger rotor system. In that system, it's recommended to turn the rotor backward after shutdown to prevent coking in the labyrinth seal... Turning forward won't rotate the engine because of the freewheeling unit.
In most cases, the cause for N2 rub or seizure is carbon buildup on the rotating labyrinth seal of the power turbine rotor. When this problem is experienced, owners and operators should refer to the above referenced DDA Commercial Service Letters reprinted as part of this Hughes Service Information Letter.
As stated in CSL-1037, walking the main rotor backwards while the engine is cooling after shutdown will definitely help to eliminate this cause for seizure and will not harm the engine.
The parent thread about not turning 429/135 backward is very interesting, and not something I would have thought of...