▌ APPLICATION NOTE · OCTOBER 2026 · SLEWING UNIT AND ROLLERS Slewing Unit and Rollers: Wear Points, Lubrication and When to Replace Two systems keep a tower crane moving: the slewing unit, which turns the upper structure, and the rollers, which carry the trolley along the jib. Both work quietly and both fail gradually, which is why they reward a routine of lubrication and inspection. The first sign of trouble is usually noise, heat or a small amount of play that nobody noticed until it became a large amount. This note covers the wear points in the slewing unit and the trolley rollers, the lubrication that keeps them healthy, and the checks that decide when a part is worn out. The crane maker’s maintenance manual sets the intervals; this note explains what those intervals are protecting.
01 HOW THE SLEWING UNIT WORKS The slewing unit is the joint between the fixed mast and the rotating upper structure. It is built around a large slewing bearing with a gear ring, driven by a slewing mechanism of motor, reducer, pinion and brake. Rollers and hardened raceways inside the bearing carry the combined vertical, radial and tilting loads. Because it carries every load the upper structure applies, the slewing unit is one of the most highly stressed assemblies on the crane. Its health is measured in lubrication, backlash and the condition of the gear ring and pinion. ▌ BEARING AND GEAR RING A large slewing bearing with a gear ring carries the upper structure. ▌ MOTOR, REDUCER, PINION The slewing mechanism drives the bearing and holds it with a brake. ▌ HIGHLY STRESSED Every upper-structure load passes through the slewing unit. 02 SLEWING WEAR POINTS The first wear points are the raceway and the gear ring. Grease protects the raceway, and the gear ring needs a film of lubricant across the tooth faces. If grease is lost, contaminated or simply not replenished, the bearing runs dry and wear accelerates. The pinion teeth and the gear ring teeth should be checked for pitting, wear and backlash. Bearing bolts are the second wear point. The bearing is held to the mast and to the upper structure by a ring of bolts that must remain tight. A loose bearing bolt is a serious defect, not a minor maintenance item, and the manual will specify the torque and re-check interval. ▌ GREASE THE RACEWAY Lost or contaminated grease is the main cause of slewing bearing wear. ▌ WATCH PINION AND RING Check gear teeth for pitting, wear and excessive backlash. ▌ BEARING BOLTS A loose bearing bolt is a serious defect, not a routine adjustment. 03 ROLLERS AND TROLLEY TRAVEL The trolley travels along the jib on rollers. These carry the trolley and the lifted load, and they keep travel smooth and aligned. Rollers wear as flat spots, as play in the bearing, or as uneven contact with the rail. A worn roller may still turn, which is why the defect is often heard before it is seen. Rollers should be checked for wear and bearing play, lubricated to schedule and replaced in sets where the manual requires it. Replacing one roller and leaving its neighbours worn keeps the trolley running out of alignment. ▌ FLAT SPOTS AND PLAY Rollers wear as flat spots, bearing play or uneven rail contact. ▌ LISTEN FOR IT A worn roller is often heard before it is seen. ▌ REPLACE IN SETS Replacing one roller beside worn neighbours keeps the trolley out of alignment.
04 LUBRICATION THAT ACTUALLY WORKS Lubrication only works if it is done on time, with the right product and in the right place. The manual specifies the grease type, the quantity and the interval for the raceway, the gear ring and the rollers. Using the wrong grease, or too little of the right one, gives the same result: accelerated wear. A simple record is worth more than good intentions. A lubrication log that names the point, the date and the product makes it obvious when a point has been missed, and it turns lubrication from a habit into a controlled task. ▌ RIGHT PRODUCT, RIGHT PLACE Use the specified grease at the specified points and intervals. ▌ QUANTITY MATTERS Too little grease wears the bearing; the wrong grease does the same. ▌ KEEP A LOG A lubrication log shows at a glance which point has been missed. 05 WHEN TO REPLACE, NOT ADJUST Adjustment can correct backlash and take up small amounts of play, but it cannot restore worn metal. When gear teeth are pitted, when the raceway shows damage, when rollers are flat-spotted or when bearing play exceeds the maker’s limit, the part should be replaced. Continuing to adjust a worn component only moves the failure later and makes it more sudden. Replacement should be planned rather than reactive. Keeping a spare pinion, a set of rollers and the correct bearing bolts on site turns a potential stoppage into a scheduled job. ▌ ADJUSTMENT HAS A LIMIT Adjustment cannot restore worn metal. ▌ REPLACE AT THE LIMIT Pitted teeth, damaged raceways and excess play mean replacement. ▌ PLAN THE SPARES A spare pinion, roller set and bearing bolts turn a stoppage into a scheduled job. PROCUREMENT IMPACT ● Specify the slewing bearing, pinion and roller set against the crane model and serial. ● Confirm the grease type and quantity with the quotation, not after delivery. ● Include bearing bolts and the maker’s torque values in the order. ● Stock a spare pinion and a set of trolley rollers for critical machines. ● Ask for backlash and wear limits in writing so replacement is a decision, not a guess. WHAT TO WATCH ● Watch for new noise or heat at the slewing unit, which usually precedes visible wear. ● Watch grease condition; contaminated grease wears a bearing quickly. ● Watch bearing bolt tightness at the stated re-check interval. ● Watch roller flat spots and replace rollers in sets. ● Watch for the habit of adjusting a worn part instead of replacing it. ABOUT ZN Industrial (Shandong Zhinuo) designs and manufactures crane safety monitoring systems, positioning systems and mechanical auxiliary handling equipment for overseas construction, industrial and steel markets. Standards and regulations vary by market — local rules still govern your site. ▌ CONTACT shandongzhinuo@outlook.com +86 176 6371 0314 · en.znaqkj.com SOURCES · crane maker’s maintenance manual · ISO 12480-1 · EN 14439 |
Articles / crane
Slewing Unit and Rollers: Wear Points, Lubrication and When to Replace
The slewing unit turns the crane and the rollers keep the trolley moving. This note identifies the wear points in both systems, explains lubrication and backlash checks, and sets out when a part should be replaced rather than adjusted.
