Perhaps is due to runout on low speed coupling, including fit etc.

I have observed ~ 20 mm movement at the torque arm, if not constrained.

Options to confirm may include:

1. Evaluate the movement's period etc, and compare to low speed angular speed, and/or

2. Rotate by hand, and inspect for movement.

 

If confirmed, the following may be options to control:

1. Evaluate to retained as is, if practicable e.g. additional loads etc are acceptable, or,

2. New/refit couplings etc, and/or rotate coupling halves to minimise runout etc.

 

Regards,

Lyle

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