pylon rock
As a Huey technical instructor and maintainer for over twenty years, here's the low down on huey pylon rock. The lift link is attached to the txmn directly in front of the mast. Pylon rock is what we call an extreme low frequency vibration (occurs less than one per revolution) and after inducing in a hover has a limit of 4-5 cycles before stopping. WE DO NOT adjust the mounts if incorrect, but replace the friction dampers which are mounted on the rear two txmn mounts only. The huey transmission in held in place by five mounts, with the fifth mount being between the two rear mounts. The friction dampers mounted to the rear mounts are to reduce pylon rock in the hover and transition while the fifth mount is used at higher forward speeds. The older UH-1 has a beem between the rear mounts to attach the fifth mount, but the upgraded txmn (Bell 212 txmn) has an integeral mount on the txmn.