Tag Archive for: slewing bearing clearance

A slewing bearing rarely fails without warning. Long before it seizes or breaks, it usually develops extra movement between its rings. Measuring that movement is one of the simplest and most useful checks a maintenance team can make.

This guide explains what clearance is, which warning signs should prompt a measurement, how to take readings with a dial indicator, and how to interpret the results so you can decide whether to keep running, repair or replace the bearing.

Why Clearance Matters: What Wear Does to a Slewing Bearing

Clearance is the small amount of relative movement that is possible between the inner and outer rings of a slewing bearing. Two types are commonly checked in service:

• Axial (tilting) movement: the up-and-down movement of one ring relative to the other when a tilting load is applied.
• Radial movement: the sideways movement between the rings.

As raceways and rolling elements wear, this movement gradually increases. Extra clearance can change how loads are shared between rolling elements and how the gear meshes with its pinion, which can speed up further damage. It can also make the superstructure of the machine feel loose or unstable.

Bear in mind that wear is not the only cause of extra movement. Loose mounting bolts or a deformed supporting structure can produce similar readings, so these should be ruled out first (see Foundation Flatness and Structural Stiffness).

Warning Signs Before You Measure

The following signs suggest it is time to take measurements:

• Grinding, clicking or knocking noises during slewing.
• Jerky or uneven rotation.
• Rotation resistance that increases or fluctuates.
• Metal particles or dark discoloration in the grease.
• Visible movement or tilt at the bearing joint.
• Red-brown dust around the bolted joint, which can point to movement or loose bolts.
• Damaged or missing seals.

These symptoms can also come from lubrication problems or gear damage, so measurement helps confirm the cause. For related topics, see Common Causes of Slewing Bearing Failure and How to Prevent Them and Gear Tooth Damage in Slewing Bearings.

Preparing for Measurement

Good preparation makes the readings reliable and the job safer:

• Safety first: shut down and secure the machine, support any suspended loads and follow your site’s lock-out procedures.
• Check the bolts: confirm that the mounting bolts are tight according to the machine manual before measuring. Loose bolts can look like bearing wear.
• Inspect the structure: look for cracks or deformation in the base and the superstructure that carry the bearing.
• Clean the measuring points: make sure the reference surfaces are free of dirt, grease and rust.
• Gather tools: dial indicators with magnetic bases, a marker for position marks, a notebook and a camera.
• Note the conditions: machine make and model, operating hours, date and the position of the boom or load.

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Suggested alt text: Dial indicator on a magnetic base measuring axial movement between the rings of a slewing bearing

How to Measure Axial and Radial Clearance in Service

Note: The procedure below is general guidance. Measuring methods vary with the bearing type and machine design, so always follow the equipment manufacturer’s manual where it specifies a different procedure.

1. Park the machine on level ground, secure it, and make sure the mounting bolts are tight before measuring. Loose bolts can look like bearing wear.
2. Fix a dial indicator on a magnetic base to the stationary structure, with the tip resting on the rotating ring, so it reads the relative movement between the two rings.
3. Take readings at several evenly spaced positions around the circumference. Mark each position so you can return to it later.
4. At each position, take one reading without the tilting load and one with it, for example by changing the boom or load position as your machine allows. The difference is the movement at that position.
5. Repeat with the indicator set to read radial movement, then record all readings with the date, machine hours and working conditions.

A few habits improve the quality of your data:

• Measure at the same positions and under the same conditions every time.
• Take each reading more than once to check repeatability.
• Repeat the measurement at regular maintenance intervals, so you build a record you can compare over time.

Reading the Results: Keep Running, Monitor, Repair or Replace?

Compare your readings with the factory value or the baseline recorded when the bearing was new or first installed, and watch how they change over time. A steady increase is a stronger warning sign than a single high reading. Acceptable values depend on the bearing type, size and application, so consult the bearing or machine manufacturer before deciding to keep running, repair or replace.

The table below gives a general way to think about your results:

What you see	What it may mean	Suggested next step
Readings close to the baseline, no warning signs	Normal condition	Continue routine inspection and lubrication, and repeat measurements at regular intervals.
Small increase, or readings that differ between positions	Early wear, loose bolts or an uneven supporting structure	Recheck the bolts and the structure, measure again and monitor closely.
Readings that keep rising over several measurements	Progressive wear	Plan for replacement, discuss the bearing’s condition with the manufacturer and schedule downtime.
A sudden jump, together with noise, rough rotation or metal particles in the grease	Possible raceway or rolling element damage	Limit use, have the bearing inspected promptly, contact the manufacturer and prepare a replacement.

Whether a worn bearing can be repaired depends on the type and extent of the damage, so it should be assessed case by case. You can read more in Repair and Remanufacturing of Large Slewing Bearings.

If replacement is the right choice and you no longer have the drawing or nameplate, see our guide on how to identify and measure a slewing bearing for replacement.

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Suggested alt text: Chart of slewing bearing clearance readings rising over time compared with the baseline value

Why Choose LDB Bearing for Slewing Bearing Replacement

Luoyang Longda Bearing Co., Ltd. (LDB Bearing) was established in 1999 in Luoyang, Henan, China’s bearing production base. Our registered trademark is LDB®, and we manufacture slewing bearings and gear rings from 150mm to 4000mm in diameter, in both standard and non-standard specifications.

• Quality system: our slewing bearings and slew drives hold ISO9001:2015 certification and German TÜV certification (2019), with process and quality control from raw material entry to finished product delivery.
• Global experience: LDB products have been exported to 73 countries and regions.
• Replacement supply: we supply replacement slewing bearings for excavators and other heavy machinery, including equipment from brands such as Cat, Komatsu, Hyundai, Kubota, Hitachi, Kobelco, Volvo, Liebherr, JCB and John Deere.

If your measurements show that a replacement is needed, send your measurements, photos and machine details to LDB. Our team will review the information and confirm the specification in your quotation. Contact LDB to request a quote.

Brand names are used only to indicate the equipment on which our replacement bearings are applied, and remain the property of their respective owners.

FAQ

Q1: What is slewing bearing clearance and why does it increase?

A: Clearance is the small relative movement possible between the inner and outer rings. It increases mainly as raceways and rolling elements wear, but loose mounting bolts or a deformed supporting structure can produce similar readings.

Q2: How often should I measure clearance?

A: Follow the inspection intervals in your machine manufacturer’s manual, and measure whenever warning signs such as noise, jerky rotation or metal particles in the grease appear. Recording readings at regular intervals lets you see the trend over time.

Q3: Can loose bolts cause the same symptoms as a worn bearing?

A: Yes. Loose mounting bolts or a deformed structure can cause extra movement and noise, so always check the bolts and the supporting structure before concluding that the bearing is worn.

Q4: What clearance value means I need to replace the bearing?

A: There is no single value that applies to every bearing. Acceptable clearance depends on the bearing type, size and application. Compare your readings with the factory value or the baseline, and consult the bearing or machine manufacturer before deciding.

Q5: Can a worn slewing bearing be repaired?

A: It depends on the type and extent of the damage, the bearing design and its condition. Have the bearing assessed case by case and consult the manufacturer before deciding between repair and replacement.

Q6: What information should I send to LDB if I need a replacement?

A: Send the bearing type, main dimensions, mounting hole pattern, gear data if any, machine make and model, and clear photos. Our team will review the information and confirm the specification in your quotation. For measuring tips, see our guide on identifying and measuring a slewing bearing for replacement.