Dear Experts,

We experience a problem with one of our ID Fans. The machine train is Motor - Oil Flex - Centerhung Fan. The Fan bearings are showing high vibration. Seems like a clearance issue. The clearance between the shaft and the bearing is 2.5 mm. One of the expert suggest for a shaft repair. Shaft OD at present is 179.30mm. Required is 180 mm. Shaft repair is costly and we need a second opinion. Did any of you experience similar problems? Is there any alternative? The vibration signature is attached.


Files (1)
Fan Vibration Signature
Original Post
Becar posted:

2,5 mm? Is that real? You should talk around 0,1 mm. Replace the shaft as soon as possible to prevent catastrophic failure. And yes, you can clearly see increased mechanical looseness in your spectra. 

Sorry it is 0.25 mm. Is it worthy doing shaft repair? 

Why wait and ruin the shaft?

Check tightness of bearing housing bolts, especially top compression bolt, and also base bolts.

Shut down and roll out the bearing to inspect bearing surface and shaft surface. It is far cheaper to replace bearing (or rebuild) than to replace shaft. You cannot rely on the vibration data (casing accelerometers) to diagnose shaft damage with journal (fluid film) bearings, but it can indicate that action is needed.


My previous comments were based on the incorrect assumption that the fan had journal bearings. A tapered roller bearing should not have any clearance between bearing and shaft! There are metal spray techniques that are used to repair a worn shaft. I cannot make a recommendation for what works well, but I suspect a good result is in the hands of the craftsman. I only see the attempted repairs that do not work well!

Perhaps this search will be of help:*1b8Dtz*zy%21FVrOcD


Uhum, like Walt, i comment with assumption of using journal bearing.

for roller bearing, I think that the repair should be applied for this shaft. HVOF could be a solution, i used to apply and the result is good. I am not sure the price in your country but i think it is cheaper than the new rotor.

One of the points about mechanical looseness that is often overlooked is that it applies to the whole system; machine, foundation, anchoring system, and grout. A failure in any of these elements will almost invariably show up as "looseness", and no amount of shimming, tweaking alignment, etc will work until the basic issue has been resolved. Check your anchor bolts, grout, and concrete integrity. 

Conversions are .010 thousands and 1760 HP.

Did they pull the bearing to get these clearance numbers?  I'll guess they did and put on a new bearing at the same time.  Highly likely the  shaft is chewed up and this is number is maybe an average at best, certainly could have more clearance because worn shafting is difficult to measure accurately.  The bearing OD should be measured and compared to the housing bore.  Use the new bearing and plasti gauge if you have to.  Often when the bore is shot it will hammer out the housing.

I didn't like what appeared to be random impacting in the waveform in the Fan Bearing next to the motor.   I would have the shaft repaired as soon as possible.  Nothing good will come of running it with the loose fit!  While the fan is being repaired run the motor uncoupled, this will confirm your motor is good when you are ready to run again.

It might be good to replace bearings and housing (if suspect) when shaft is repaired. This would be starting on a fresh mowed playing field! Replacing or repairing only one part when other connected parts are not in good condition can have expensive consequences!


I agree that this needs to be corrected. Another option would be in field machining of the shaft, and then work with the bearing supplier for custom bearing liners for modified dimensions. As stated the entire machine needs to be investigated for looseness. The housing needs to be checked that the bearing seat is not damaged, as Walt stated, a possible new housing may be required. 

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