The levels on this overhung fan were not that bad but did have a couple of Mils unbalance on the impeller side bearing. After balancing, the horizontal 1X was down to .4 Mils but the vertical went from about .4 mils to .9 mils. After unbalance decreased, harmonics appear more dominant. Now the overall levels on this bearing are at .15 in/s which is normally good for any fan (1200 rpm belt driven). But this fan ran below .1 before. They said they repacked the bearings. This would have involved strapping the impeller and removing bearing caps to cleanout the grease and add new stuff. I wonder if they could have moved something in the bearings (didnt support impeller well enough)? Does this sound like a typical looseness problem or what else could be going on? I will recheck in a day.

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Looks like looseness to me. Have you tried cross channel phase to confirm.

This is not a good match for your symptoms, but I've had a few belt driven fans where the sheave runout made a mechanical 1X in the direction of the belt pull that would over-ride good balance. When un-balance weights were added to reduce the vibration/motion! caused by the sheave, the vibration at right angles to the belts naturally increased. With a nice big gyroscopic fan the effect is not limited to the drive end bearing.

Jbalco,
What plane did you balance?, the nearest or the far from the impeller side bearing, I believe the right plane would the nearest from the impeller side bearing.
Regards.

How many blades does the fan have? 6?

Overhung fans are well known for increasing in one direction when lowered in another. Did you do a two plane balance or single plane?

8 Blades balanced on impeller side bearing. Paddle style blades. Maybe less than 1 foot wide. There really is no 2nd plane and the far bearing levels were well below a half a mil.

Also have a look at www.vibinst.org posting ''the rules of balancing''!
Regards, Arie Mol, NL

Possibly the bearing has a little too much internal clearance and when the force due to unbalance was reduced the bearing is showing the looseness more now. The centrifugal force of the unbalance was possibly just right to hold the shaft to one side.