For tapered-bore spherical roller bearings, mounting clearance is checked by measuring the reduction in radial internal clearance and confirming that enough clearance remains. Start with the correct bore type and clearance class, measure before mounting, and use the instructions for the exact bearing and shaft arrangement. A clearance chart alone does not specify how far to tighten the lock nut.
The tables below distinguish unmounted clearance from mounting reduction. They also show why a cylindrical-bore bearing and a tapered-bore bearing with the same nominal bore do not necessarily start with the same clearance.
Spherical Roller Bearing Clearance Chart: CN, C3 and C4
Radial internal clearance is the total radial movement available between the rings under defined measuring conditions. CN means Normal clearance; C3 is greater than Normal, and C4 is greater than C3. C2 is smaller than Normal; C5 is greater than C4. These are clearance groups, not accuracy grades or load ratings.
Read each bore interval as “over” the first number and “up to and including” the second. All values below are unmounted radial clearances in micrometers (µm), not clearance reductions or operating targets. 1,000 µm = 1 mm.
Cylindrical-bore bearings: unmounted clearance
| Bearing bore d (mm) | CN (µm) | C3 (µm) | C4 (µm) |
|---|---|---|---|
| 50 < d ≤ 65 | 40–65 | 65–90 | 90–120 |
| 65 < d ≤ 80 | 50–80 | 80–110 | 110–145 |
| 80 < d ≤ 100 | 60–100 | 100–135 | 135–180 |
| 100 < d ≤ 120 | 75–120 | 120–160 | 160–210 |
| 120 < d ≤ 140 | 95–145 | 145–190 | 190–240 |
| 140 < d ≤ 160 | 110–170 | 170–220 | 220–280 |
| 160 < d ≤ 180 | 120–180 | 180–240 | 240–310 |
| 180 < d ≤ 200 | 130–200 | 200–260 | 260–340 |
Tapered-bore bearings: unmounted clearance
| Bearing bore d (mm) | CN (µm) | C3 (µm) | C4 (µm) |
|---|---|---|---|
| 50 < d ≤ 65 | 55–75 | 75–95 | 95–120 |
| 65 < d ≤ 80 | 70–95 | 95–120 | 120–150 |
| 80 < d ≤ 100 | 80–110 | 110–140 | 140–180 |
| 100 < d ≤ 120 | 100–135 | 135–170 | 170–220 |
| 120 < d ≤ 140 | 120–160 | 160–200 | 200–260 |
| 140 < d ≤ 160 | 130–180 | 180–230 | 230–300 |
| 160 < d ≤ 180 | 140–200 | 200–260 | 260–340 |
| 180 < d ≤ 200 | 160–220 | 220–290 | 290–370 |
These selected ranges follow the conventional clearance tables associated with ISO 5753-1:2009. They apply to unmounted bearings under zero measuring load, as far as standardized. Check the supplied specification for special designs, restricted clearance ranges and sizes outside these tables. The standard defines clearance values; it does not prescribe a universal installation drive-up distance.
22216 Bearing Clearance: Read the Bore Boundary Correctly
A 22216 E bearing has an 80 mm bore. At exactly 80 mm, use the 65 < d ≤ 80 row, not the next row. For a cylindrical-bore version, CN is 50–80 µm and C3 is 80–110 µm. For a tapered-bore version, CN is 70–95 µm and C3 is 95–120 µm. Confirm the complete suffix and supplied clearance class before using either range.
For dimensions and series comparisons, use the separate spherical roller bearing size chart. Boundary dimensions and internal clearance are different specifications.
Initial, Residual and Operating Clearance
Initial clearance is measured before mounting. Residual clearance is what remains after mounting, with the bearing at a stable reference temperature. Operating clearance is the clearance in service, after fits and temperature differences have taken effect. A satisfactory cold measurement does not, by itself, prove that the operating clearance will be suitable.
For a before-and-after mounting check at comparable temperatures: clearance reduction = measured initial clearance − measured residual clearance. If initial clearance is 0.180 mm and residual clearance is 0.110 mm, the reduction is 0.070 mm (70 µm).
Clearance reduction = initial clearance − residual clearance
Example: 0.180 − 0.110 = 0.070 mm (70 µm).
Compare measurements at stable, comparable temperatures. This arithmetic example does not specify installation acceptance limits.
Cylindrical Bore vs. Tapered Bore: What Changes During Mounting?
A cylindrical-bore bearing fits directly on a cylindrical shaft seat. Select the shaft and housing fits from the load direction, load level and operating conditions. Where an interference fit is required, use an approved mechanical or thermal mounting method. Apply mounting force to the ring being fitted; transmitting that force through the rollers can damage the raceways.
A tapered-bore bearing mounts on a tapered shaft seat, an adapter sleeve or a withdrawal sleeve. Axial movement up the taper expands the inner ring and reduces radial clearance. K commonly identifies a 1:12 taper and K30 a 1:30 taper; verify the designation in the relevant catalog. The choice is not determined by an 80 mm shaft-diameter cutoff.
Keep the bearing rings and rollers centered during handling and mounting. Where practical, mount with the shaft horizontal and rotate a ring to align the rollers. A displaced roller set can make the bearing appear to have little or no clearance before the fit has been established.
Figure 1. Simplified ring-seat interfaces. Taper is exaggerated; rollers, outer ring and locking components are omitted.
How to Measure Spherical Roller Bearing Clearance with a Feeler Gauge
Use this method on open bearings where the rollers are accessible and the mounting instructions permit it. Gauge access, bearing weight and support conditions matter more than a single bore-size limit. Measure both roller rows and record their readings.
Figure 2. Typical unloaded measuring zones for the two support arrangements shown. Circular roller-end symbols represent one row schematically; measure both rows. For heavy rings or other support conditions, follow the specified correction procedure.
Prepare the bearing and seats. Remove burrs and contamination, check shaft and sleeve dimensions, and confirm the full bearing designation. Let heated components stabilize before making a final clearance comparison.
Align the rings and rollers. Rotate a ring gently, then support the assembly as directed. On an unmounted upright bearing resting on its outer ring, the unloaded measuring zone is normally at the top. On a bearing supported by a horizontal shaft, it is normally at the bottom. Use the prescribed zone for the actual support arrangement.
Measure initial clearance in both rows. Insert a clean feeler blade between an unloaded roller and the outer-ring raceway. Use light resistance; do not force a thick blade into the gap or move a roller to make it fit. Record the measured clearance before drive-up.
Advance the bearing in controlled increments. Use the specified lock nut, hydraulic nut or mounting equipment. Re-measure clearance as mounting progresses and calculate the reduction from the recorded initial value.
Check both acceptance conditions. The reduction must meet the applicable mounting range, and the remaining clearance must meet the specified minimum for that bearing and clearance class. Stop if these conditions cannot both be met.
Secure and verify the assembly. Engage the specified locking device and recheck accessible clearance after final locking and assembly. Record the final result before commissioning.
Large, thin or heavily loaded rings can deform under their own weight. A single gap reading may then be misleading. Use the manufacturer’s specified multi-position measurement and correction procedure. Do not treat readings taken at arbitrary positions as interchangeable, or apply a three-point formula without its matching support and measurement diagram.
Axial Drive-Up: Use a Defined Starting Position
Where seals prevent access to the rollers, use an approved mounting method that does not require a feeler gauge. Axial drive-up measures movement along the taper from a specified starting position. A hydraulic nut supplies the force; a dial indicator measures travel. Neither tool establishes the correct starting position by itself.
For a pressure-referenced hydraulic procedure, both the initial seating pressure and the subsequent axial travel must match the bearing, sleeve and tool arrangement. Do not substitute a conventional drive-up table for a pressure-referenced procedure. Likewise, do not convert clearance reduction into axial movement using a universal 16×, 18×, 39× or 42× multiplier.
Taper ratio describes geometry, not a complete mounting model. Ring expansion, shaft and sleeve compliance, and the initial seating condition affect the relationship between travel and clearance reduction. Hollow shafts and non-steel shafts may require different guidance.
Worked Example: Calculating Clearance Reduction for a 190 mm Bearing
Consider an open 190 mm tapered-bore bearing with a 1:12 taper and CN clearance. Its nominal bore falls in the 180 < d ≤ 200 mm interval, for which the selected unmounted CN range is 0.160–0.220 mm. Suppose the measured clearance is 0.180 mm before mounting and 0.080 mm after mounting at a comparable, stable temperature. The calculation below illustrates the measurement relationship.
| Check | Calculation or value |
|---|---|
| Measured initial clearance | 0.180 mm |
| Calculated clearance reduction | 0.180 − 0.080 = 0.100 mm (100 µm) |
| Measured residual clearance | 0.080 mm (80 µm) |
These measurements establish the amount of clearance reduction; they do not establish that the mounting is acceptable. Compare the measured reduction and residual clearance with the requirements for the exact bearing, clearance class and shaft or sleeve arrangement. Both conditions must be satisfied. Do not use the unmounted CN range as the target residual clearance, or treat the values in this example as installation limits.
When Should You Use C3 or C4 Clearance?
Choose the initial clearance class to accommodate the predicted fit and thermal effects while achieving the required operating clearance. An interference fit on the inner ring generally reduces clearance; an interference housing fit can also reduce it. If the inner ring runs hotter than the outer ring, the temperature difference usually reduces clearance further.
There is no universal rule that an operating temperature above 70°C requires C3. The temperature difference between the rings, actual interference, bearing size and machine duty all matter. C3 or C4 may be appropriate for some demanding applications, but more clearance is not automatically better. Do not change the specified clearance class without checking the arrangement.
Housing, Sleeve and Commissioning Checks
An adapter sleeve can position a bearing on a plain cylindrical shaft, but the sleeve, locking device and axial retention must suit the application. Sleeve friction is not a substitute for checking the complete axial load path. A bearing’s basic static load rating is not the permissible axial holding force of the sleeve assembly.
In a split housing, verify the housing seat, cap assembly, locating components and provision for shaft thermal expansion. A floating bearing arrangement must retain its intended freedom to move. Recheck accessible clearance after final assembly where the mounting procedure requires it.
During the initial run, monitor temperature, vibration and noise against the machine’s commissioning criteria. An abnormal trend calls for investigation of fits, lubrication, alignment and clearance. Do not keep tightening the lock nut to cure noise, or diagnose clearance from housing temperature alone.
FAQ
Can I reuse the mounting measurements from the bearing I removed?
Keep them as maintenance history, but measure the replacement bearing independently. Bearings with the same designation and clearance class can have different initial clearances within the permitted range. Previous nut position or drive-up travel does not establish the new bearing’s fit.
Does a bearing that turns freely by hand have the correct clearance?
Free rotation is a useful assembly check, but it does not quantify clearance or interference. Acceptance still requires the specified measurement or validated mounting procedure. A hand check also cannot predict the effect of operating temperatures.
Can a dial indicator replace a feeler gauge for a clearance check?
They measure different things in a drive-up setup. A dial indicator tracking axial travel measures displacement along the taper, not radial clearance directly. A direct radial-clearance measurement with an indicator needs its own controlled support and measuring-load procedure.
What to Confirm Before Ordering or Mounting
For help checking a bearing and mounting arrangement, contact us with the full designation, clearance suffix, shaft and housing dimensions, sleeve reference, speed, loads and expected temperatures. For an installation check, include the measured initial clearance and the applicable mounting instruction.
Technical basis: unmounted clearance ranges are associated with ISO 5753-1:2009. Mounting reduction, minimum residual clearance, axial travel and hydraulic seating pressure are separate requirements taken from the instructions for the supplied bearing. Use the approved machine drawing and product-specific procedure for installation acceptance.
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