Shaft is difficult to turn

CodeReason for conditionPractical solution
1Grease or oil is breaking down because it is the wrong type for operating conditions.Consult lubricant manufacturer to determine proper type of lubricant. Check miscibility if grease or oil has been changed from one type to another.
2Low oil level. Lubricant is being lost through the seal.
Insufficient grease in the housing.
Oil level should be just below the centre of the lowest rolling element in the bearing (fig 1).
Fill housing 1/3 to 1/2 with grease.
3Housing is fully packed with grease, or the oil level is too high. This causes excessive lubricant churning, high operating temperature or oil leakage.Purge grease until the housing is 1/2 filled with grease.
For oil lubricated bearings, reduce the oil level to just below the centre of the lowest rolling element (fig 2).
4Bearing has inadequate internal clearance for conditions where external heat is conducted through the shaft. This causes the inner ring to expand excessively.Check whether overheated bearing had clearance according to original design specification (fig 3). If so, then change to bearing with increased radial clearance, i.e. Normal to C3 or C3 to C4. If not, order to specification. Check with SKF if the bearing designation has become illegible.
5Dirt, sand, carbon, or other contaminants are entering the bearing housing.Clean the bearing housing. Replace worn seals or improve the seal design to obtain adequate bearing protection (fig 4).
6Water, acids, paints or other corrosives are entering the bearing housing.Install a protective shield and/or flinger to guard against foreign matter (fig 5). Improve seals.
Housing bore is out-of-round. Housing is warped or distorted. Supporting surface uneven.
Housing bore is undersized
Check and scrape the housing bore to relieve pinching of the bearing. If necessary turn the housing bore to the correct dimension. Ensure that the supporting surface is flat and that the shims cover the entire area of the housing base (fig 6).
Housing bore is undersized if non-locating bearing is changed from separable to non-separable bearing, e.g. from cylindrical roller bearing to deep groove ball bearing.
10Chips, dirt etc. were not removed from housing before assembling the bearing unit.Carefully clean (fig 7), and apply fresh lubricant.
12Contact (rubbing) seals are dried out or have excessive spring tension.Replace contact (rubbing) seals with seals having correct spring tension (fig 8). Lubricate seals.
Rotating seals or flingers are rubbing against stationary parts.Check the running clearance of the rotating seal or flinger to eliminate rubbing (fig 9). Correct the alignment.
15Cross location.Insert shim between housing and cover flange to relieve axial preloading of bearing (fig 10).
16Two locating bearings on one shaft. Insufficient clearance in bearing caused by excessive shaft expansion.Move the covers in one of the housings outwards (fig 11). Use shims to obtain adequate clearance between the housing and the outer ring. Apply axial spring load on the outer ring, if possible, to reduce axial play of the shaft.
19Adapter sleeve is tightened excessively.Loosen the locknut and sleeve assembly. Retighten it sufficiently to clamp the sleeve on to the shaft but be sure the bearing turns freely (fig 12).
25Shaft is bending due to incorrect shoulder diameter.Remachine the shaft fillet to relieve stress (fig 13). The application may require a shoulder collar. Check that abutment dimension is in accordance with SKF recommendations.
26Shaft shoulder is rubbing against bearing seals.Remachine the shaft shoulder to clear the seals (fig 14). Check that shoulder diameter is in accordance with SKF recommendations.
27Inadequate support in the housing is causing the outer ring to distort.Remachine the housing fillet to relieve stress (fig 15). Check that abutment dimension is in accordance with SKF recommendations. The application may require a shoulder collar.
28Distorted bearing seals.Remachine the housing shoulder to clear the seals (fig 16).
29Shaft and inner ring are distorted.Remachine shaft fillet to obtain the proper support (fig 17).
30Housing and outer ring are distorted.Remachine the housing fillet to obtain the proper support (fig 18).
Incorrect linear or angular alignment of two or more coupled shafts with two or more bearings.Correct alignment by shimming the housings. Ensure that the shafts are coupled in a straight line, especially when three or more bearings operate on one shaft. Be sure to use full support shims (fig 19).
37Washer prong is rubbing against the bearing.Remove the locking washer. Straighten the prong or replace with a new washer (fig 20).
45Shaft or housing shoulders or locknut face out-of-square with the bearing seat.Remachine parts to obtain squareness (fig 21).
47Bearing seat diameter is oversized, causing excessive inner ring expansion. This reduces bearing clearance.Grind shaft to get a proper fit between the shaft and the bearing inner ring If regrinding is not possible change to bearing with larger radial clearance (fig 22).
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