Measure swing bearing clearance with the machine level, the bucket just clear of the ground, and a dial indicator mounted between the upper structure and the undercarriage. Take three readings: axial lift of the upper structure, and radial play front to back and side to side. Compare each against the manufacturer's limit for the model. Radial readings usually rise faster than axial ones, and it is radial wear that lets the upper structure move under load and damages the swing pinion and the ring gear.
What you will notice
| Symptom | What it usually points to |
|---|---|
| A rumble or knock heard in the cab when swinging | Clearance that has opened beyond the point where the bearing surfaces stay loaded. Measurement decides whether it is the bearing, the pinion or the gearbox. |
| Upper structure visibly moving on the undercarriage under load | Late-stage radial wear. By this point the swing pinion teeth have usually suffered as well, so the two are inspected together. |
| Swing pinion or ring gear teeth marked or chipped | Wear in the bearing allows the pinion to run at the wrong depth. Replacing the pinion without addressing clearance repeats the failure. |
| Swing feels loose, then tight, at the same point each turn | Uneven clearance or a damaged race section, which a single reading will not show. Take the readings at three positions around the circle. |
| Grease purges unevenly around the swing circle | A lubrication fault rather than a clearance fault, but it is the usual reason a bearing reaches its limit early. Correct it before measuring, or repeat the measurement after. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Normal progressive wear | Load cycles and hours. A bearing in daily service wears slowly and predictably, which is why recording the readings matters more than any single figure. |
| Under-lubrication of the swing circle | Grease that reaches one sector and not the rest. Wear then becomes uneven around the race, and the loosest sector sets the reading. |
| Water or grit entering past the seal | A damaged swing circle seal lets abrasive material into the race. The seal is cheap and the bearing is not, which is the whole argument for checking it. |
| Loose mounting bolts or structure | A vertical reading that looks like bearing wear can come from mounting bolts that have worked loose or from cracking around the mounting face. |
| Impact load or an operating practice change | Hammer work, dragging the bucket sideways and swinging into a bank all load the circle in directions it was not sized for. |
The three readings and what each one points at
| Reading | How to read it |
|---|---|
| Axial lift, bucket just clear of the ground | Boom raised slowly so the upper structure lifts. Movement here is vertical clearance, and mounting bolts are checked before the bearing. |
| Radial play, front to back | Boom used as a lever to push and pull the structure. Read total movement, because the limits are quoted as total clearance. |
| Radial play, side to side | Swing the arm to load the structure sideways and repeat. On most machines this is the direction that reaches its limit first. |
| Repeat each reading three times | Three consistent figures are a measurement. Three scattered figures mean the setup is moving and the number is worthless. |
| Repeat at three positions around the circle | A bearing worn unevenly reads differently at different swing positions. The worst figure is the one you act on. |
How to confirm it
- Read the specification before touching the machine
Get the axial and radial clearance limits and the measuring positions from the service documentation for the model. Swing bearing work is expensive enough to deserve a real answer, and a measurement with no limit to compare it against is only a number.
- Position the machine so the readings mean something
Level ground, bucket on the ground with the arm slightly extended, so the structure is stable without being pre-loaded, and the machine at operating temperature. Cold, the lubricant film is different and the reading comes out tighter than the machine actually is in service.
- Mount a dial indicator between the two structures
Magnetic base on a clean, flat machined surface of the undercarriage frame, never on a painted panel, with the plunger touching a machined surface of the upper structure as close to the race as you can reach. Zero the indicator and press lightly on the structure to confirm the base cannot shift.
- Take the axial reading first
With the bucket just clear of the ground, raise the boom slowly so the upper structure lifts and the indicator reads vertical movement. Record the maximum and let the structure settle. Repeat three times and compare the figures before moving on.
- Take both radial readings using the boom as a lever
Bucket down, boom extended, push and pull the structure forward and backward and read total movement. Then swing the arm to load it sideways and repeat. Read total movement rather than half of it, and repeat at three positions around the circle.
- Record the figures and repeat after greasing if the result is close to the limit
Write the readings down with the hour meter figure and the date. If a reading is marginal, grease the swing circle properly and repeat, because a dry bearing reads loose and a lubricated one may come back inside limits. Guangzhou Shenyue Machinery Technology Co., Ltd. asks for all three readings, with the machine model and serial number, whenever a swing bearing is quoted.
What to do about it
Within limits: record the figures and the date. Wear is progressive, so the rate of change between services is more informative than any single reading, and the record is what turns a measurement into a decision.
Radial play over limit with axial play inside it: the bearing assembly needs attention, and the swing pinion and ring gear should be inspected at the same time, because radial wear loads the teeth at the wrong depth and marks them.
Axial play over limit: check the mounting bolts and the structure around the bearing first. Bolts that have worked loose or a cracked mounting face produce a vertical reading that looks exactly like bearing wear.
Marginal clearance with poor grease condition: grease the circle thoroughly and re-measure. It is not a repair, but it separates a genuine wear problem from a lubrication problem in a few minutes.
If the bearing is to be replaced, plan the job as a set. Guangzhou Shenyue Machinery Technology Co., Ltd. quotes swing bearings, swing pinions and mounting hardware as genuine, OEM-quality or remanufactured exchange lines, holds 3,000+ part types on the shelf with 100,000+ part numbers available to order, and confirms fitment from the model and serial number rather than from a photograph.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Swing bearing | Genuine; OEM-quality. Confirm by model and serial number break. |
| Swing pinion | Genuine; OEM-quality. Normally replaced with the bearing if teeth are marked. |
| Mounting bolts and hardware | Genuine; OEM-quality. Torque values are model-specific. |
| Swing circle seal | Genuine; OEM-quality. Replace whenever the bearing is disturbed. |
| Swing circle grease | Specified grade; quantity per point from the lubrication chart. |
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
How do I know when a swing bearing needs replacing?
When radial or axial play exceeds the limit for the model, or when the rate of wear between services has accelerated. Noise and visible movement of the upper structure come later than the measurement does.
Can I measure swing bearing clearance without a dial indicator?
Not reliably. A feeler gauge or a visual check cannot resolve the fractions of a millimeter the limits are written in. A dial indicator on a magnetic base is the minimum equipment for the job.
Does greasing the swing circle change the clearance reading?
It can change it by more than you would expect. A dry bearing reads loose, so grease the circle and repeat the test before concluding anything, especially when the reading is only slightly over the limit.