Two complaints arrive at our desk under the same heading — "the swing group is noisy" — and they carry prices an order of magnitude apart. A worn swing reduction can often be rebuilt in place with parts; a worn swing bearing is a crane job, several days of downtime and a five-figure part on the larger classes. Telling them apart before a spanner is lifted is the single most valuable diagnostic decision in the swing system. This is how the technical team at Guangzhou Shenyue Machinery Technology Co., Ltd. separates them.
Two very different parts
- The swing reduction. A planetary gearbox bolted between the swing motor and the upper structure. It multiplies the motor's torque and carries the swing load through gears and bearings that run on oil.
- The swing bearing. The large-diameter slewing ring between the undercarriage and the house. It carries the entire weight of the upper structure, the attachment and the load, and it never turns fast — but it carries everything.
Both are in the swing group, both can produce noise, and neither can be identified from the other's symptoms unless the test is done deliberately.
Symptom to component
| What the operator reports | More likely home of the fault |
|---|---|
| Continuous rumble that rises with swing speed | Swing reduction bearings or gear mesh |
| Knock or clunk once per revolution, felt at the house | Swing bearing race, or a broken tooth in the reduction |
| Metal in the swing reduction oil, or grey paste on the plug | Reduction gear and bearing wear — stop swinging |
| Visible play when the boom tip is pushed by hand | Swing bearing clearance, or the reduction's pinion and gear backlash |
| Grease escaping at the bearing seal line, gap visible at the race | Swing bearing — greasing buys time, not a cure |
| Swing drifts, slows or loses power with the motor hot | Swing motor or its relief, not the reduction or the ring |
Three checks that decide it
- Drain and inspect the reduction oil. Metal or a grey paste in the oil condemns the reduction regardless of what the bearing is doing. This is a five-minute check and it is the one most often skipped.
- Measure swing bearing clearance. With the attachment positioned as the service manual specifies, measure the tilt and the play at the bearing, then check the grease for metal. A figure outside the manual's limit is a bearing decision, not a gearbox one.
- Listen with the swing isolated. Where the machine allows it, a slow swing with the attachment close in and low loads the group differently from a fast swing, and the two behaviours separate a gear mesh fault from a race fault more reliably than any description. A dial gauge and an oil sample beat an opinion, and a written number beats both.
What a swing bearing replacement actually involves
Replacing a swing bearing means separating the house from the undercarriage: the attachment comes off or is supported, the swing motor and reduction are removed, the ring bolts are released in the specified sequence, and the new ring is torqued to the manual's pattern and figures. Two details decide whether the new bearing lasts. First, the mounting face and the bolt holes on both the house and the frame must be inspected and corrected — a bearing bolted to a distorted face wears its race unevenly from the first hour. Second, the swing reduction's pinion engagement and backlash must be set after fitting, because the ring's tooth geometry is part of a matched pair with the pinion. Where the reduction is worn too, doing both in one strip is cheaper than doing them separately. On the larger classes the same exercise costs several times as much, which is why the clearance measurement is worth taking seriously.
Guangzhou Shenyue Machinery Technology Co., Ltd. has specialised in Kobelco parts since 2007, with 4 warehouses over 1000 m² in Guangzhou, 3,000+ part types on the shelf and 100,000+ part numbers available to order through original supply channels. Shenyue is an independent supplier of excavator parts and is not an authorized dealer or distributor of Kobelco Construction Machinery Co., Ltd.; for Kobelco, Hino, Isuzu, Yanmar, Cummins, Kawasaki, Nabtesco, KYB and KPM we supply genuine parts ordered through original supply channels alongside quality replacement alternatives, at prices close to agent level, and the five brands we are formally authorized for are Mitsubishi, Garrett, TONGMYUNG, Marusan and NIKURA. Read the swing motor detail in our SK200-8 swing motor and reduction guide, browse the hydraulic components category, and check a reference in the part number search. Bearing specification data is published by manufacturers such as SKF.
Frequently Asked Questions
How do I tell whether the swing reduction or the swing bearing is worn?
Three checks separate them. Drain and inspect the swing reduction oil for metal or grey paste, which condemns the reduction regardless of the bearing. Measure the swing bearing clearance and tilt against the service manual figure, and check the grease for metal. Then listen to a slow, low-load swing against a fast swing, which separates a gear mesh fault from a race fault. Guangzhou Shenyue Machinery Technology Co., Ltd. asks for the oil condition and the clearance reading before quoting either part.
Can a noisy Kobelco swing group be repaired without replacing the swing bearing?
Often yes. If the noise is a continuous rumble that rises with swing speed and the reduction oil contains metal, the fault is the reduction gearbox, which can be rebuilt with parts. A knock once per revolution with visible play at the house points at the bearing race. Because the two repairs differ enormously in cost and downtime, Guangzhou Shenyue Machinery Technology Co., Ltd. quotes them separately and only after the evidence has been checked.
What is involved in replacing a Kobelco swing bearing?
The house must be separated from the undercarriage: the attachment is removed or supported, the swing motor and reduction come off, and the ring bolts are released and retorqued in the manufacturer's sequence and figures. The mounting faces must be inspected and corrected, and the swing reduction pinion engagement and backlash must be reset afterwards. Guangzhou Shenyue Machinery Technology Co., Ltd. quotes the bearing, the bolts and the swing reduction parts as separate lines so worn items can be renewed in the same strip.
Which parts make up the Kobelco 20 tonne class swing group?
The group is three separate purchases: the swing motor, normally the M5X130 family quoted as YN15V00077F1 / YN15V00055F1 / YN15V00035F1; the swing reduction, commonly quoted as YN32W00025F1 / YN32W00022F2 / YN32W00019F1; and the swing bearing. Each is identified from its own plate or stamped number. Guangzhou Shenyue Machinery Technology Co., Ltd. confirms the unit number against the machine before quoting.