After a shutdown, do not treat coupling alignment as a single cold-offset reading. Confirm foundation condition, soft foot, shaft runout, coupling condition and the specified thermal-growth target before moving the motor or gearbox.
High vibration, hot coupling, repeated element wear, seal distress or a change in drive noise after maintenance.
Laser or dial alignment results, soft-foot checks, shaft/coupling runout, base movement, hold-down condition and the OEM cold-alignment target.
Correct the mechanical cause first; move the machine only after repeatable measurements show the offset is real and not caused by loose feet, pipe strain or a damaged coupling.
Record these values before touching the equipment
- kiln stopped duration and casing temperatures
- motor and gearbox bearing temperatures before shutdown
- as-found horizontal and vertical offset/angle
- soft-foot result at every foot
- coupling hub runout and element condition
- foundation, grout, chocks and hold-down observations
V3 rule: preserve the as-found condition. The first measurement is part of the diagnosis, not paperwork after the repair.
1. Stabilize the machine train
Lock out the drive, allow the train to reach the alignment condition required by the OEM procedure, clean the base and verify there is no loose hardware. Alignment work made while one machine is still thermally distorted can create a false correction.
2. Check mechanical integrity before alignment
Inspect coupling hubs, flexible elements, keys, shafts, base plates and hold-downs. Measure shaft or hub runout where the coupling design permits. A bent shaft, damaged hub or loose base cannot be corrected with shims.
3. Eliminate soft foot and external strain
Check each motor and gearbox foot systematically. Correct dirt, burrs, distorted shims and uneven support. Where connected auxiliaries can impose strain, confirm the train does not move when connections are released according to site procedure.
4. Measure offset and angular error
Take repeatable readings in both planes and compare them with the specified cold target, including any intentional thermal-growth offset. Rotate shafts as required by the chosen method so runout influence can be recognized.
5. Correct, tighten and reverify
Make controlled shim and horizontal moves, tighten in the prescribed sequence and repeat the full measurement. The job is complete only when the final reading is stable after tightening and the coupling can be assembled without forcing.
6. Control measurement quality before accepting the result
Alignment readings are only useful when they are repeatable. Check the laser brackets or dial fixtures for looseness and bracket sag, confirm the shafts can be rotated through the required positions without disturbing the setup, and repeat the measurement after tightening the machine feet. If the result changes materially after bolt tightening, investigate soft foot, base distortion or shim instability before making another correction. Record horizontal and vertical offset and angular results separately so the maintenance team can distinguish a parallel move from an angular correction.
7. Verify the cold target and thermal-growth assumption
The correct cold alignment is not always zero-to-zero. Motor, gearbox and driven equipment can move by different amounts as their housings, bases and lubricant systems reach operating temperature. Use the coupling or drive OEM target, previous hot/cold survey data, or an established plant thermal-growth study. If a machine repeatedly aligns well cold but shifts into high vibration or coupling distress after warm-up, recheck the thermal target rather than repeatedly forcing the cold reading closer to zero.
Where practical, compare bearing-housing temperatures and stable operating condition from a known-good run. The purpose is to reproduce the designed shaft relationship at operating temperature, not to produce the prettiest cold laser screen.
8. Inspect coupling type and assembly condition
Flexible couplings tolerate limited misalignment, but that tolerance is not a maintenance target. Inspect element condition, hub fit, key or locking device, bolt condition and the specified gap or axial position for the installed coupling type. Elastomeric elements, gear couplings and disc couplings fail in different ways; use the manufacturer’s inspection criteria. If the coupling shows asymmetric wear, fretting or heat discoloration, preserve that evidence because it can confirm the direction and duration of the misalignment.
Diagnostic matrix
Return-to-service acceptance
- repeatable final alignment in both planes against OEM target
- soft foot removed or within plant/OEM limit
- no forced coupling assembly
- hold-downs torqued and witness-marked
- baseline vibration and temperatures recorded after restart
Common mistakes that create repeat failures
- aligning before checking soft foot
- using one reading without repeatability
- ignoring thermal growth
- compensating for a damaged coupling with machine movement
- failing to record the as-found condition
Engineering note
This guide is a field troubleshooting workflow, not a substitute for the equipment manufacturer’s maintenance manual. Use the OEM limits for clearances, alignment, pressures, temperatures, wear, torque and restart criteria. Where plant history exists, compare with a known-good baseline under similar load and temperature rather than a generic number.