Cone Crusher Eccentric and Eccentric Bushing Maintenance

The cone crusher eccentric and eccentric bushing form one of the most critical mechanical groups producing the crushing motion of a cone crusher. The circular motion coming from the drive is converted by the eccentric into a gyratory motion of the head and main shaft. To prevent direct metal-to-metal contact during this motion, bronze bushings running on an oil film work inside the eccentric and on the related bearing surfaces. When correct lubrication, correct clearance and correct assembly are not maintained, crusher performance drops; rising temperature, oil analysis findings, metallic noise, surface smearing and ultimately serious mechanical damage can occur.

If you would like to look at the general working logic of cone crushers in a broader context, the guide What Is a Cone Crusher? Working Principle, Setting, Lubrication and Maintenance Guide is a useful starting point. In this article we focus directly on the eccentric and eccentric bushing group.

What Do the Eccentric and Eccentric Bushing Do?

In a cone crusher, the main crushing motion is created not by the head rotating exactly on centre but by its gyration along an eccentric path. The part producing this motion is the eccentric. When the eccentric is rotated by the drive system, it creates a deliberate offset between its geometric centre and the working axis. As a result, the main shaft and head perform a controlled oscillating, gyrating motion instead of turning straight on a fixed axis.

For this system to work safely and efficiently, there must be no direct dry friction between the eccentric and the shaft/bearing surfaces. This is where the eccentric bushing comes in. Usually made of bronze-based alloys, these bushings act as load-bearing plain bearing surfaces. When the oil film forms, the load is carried through the oil layer rather than directly by the metal surfaces. Friction is reduced, the surfaces are protected and the crusher runs more steadily.

In short, this group has three basic functions:

• Producing the gyratory motion and providing the main crushing kinematics,
• Carrying and distributing the load,
• Limiting wear and heating through controlled sliding on an oil film.

Design and Main Components

Although details vary by model, a typical cone crusher eccentric group includes the following:

• Eccentric body: Receives the rotation from the drive and creates the eccentric geometry.
• Inner and/or outer bushing surfaces: Work on an oil film against the main shaft or related bearing surfaces.
• Bronze alloy bushings: Usually copper-based alloys; depending on the model they may be tin bronze, leaded bronze or other compositions.
• Oil grooves and distribution paths: Ensure oil reaches the bushing surface at sufficient flow and from the right direction.
• Locating and seating surfaces: Critical for the bushing to fit tightly in the eccentric, not to rotate and to transfer heat correctly.

In some designs the bushing is installed in the eccentric with an interference fit. In others, a poured backing or similar special seating method described by the manufacturer is used. Whatever method is used on site, the principle is the same: the bushing must sit firmly in the eccentric, must not rotate in its bore, the geometry must not be distorted and the specified oil clearance must be maintained in operation.

Signs of Wear and Failure

Eccentric bushing failures rarely happen all at once; they first give small signals. Reading these signals early prevents damage to the main shaft, eccentric body, gears and other expensive parts. The following are the warnings most frequently seen on site:

• Rising oil return temperature: When the oil film weakens or friction increases, the temperature of the returning oil rises.
• Increase in copper, tin or lead in oil analysis: Wear particles may be coming off the bronze bushing surface.
• Metallic noise: Can be associated with loss of oil film, excessive clearance or surface damage.
• Unstable running under load: The crusher’s sound changes, current may fluctuate and product size can become unstable.
• Abnormal vibration or knocking: Seen especially when clearance increases or the bushing loosens in its bore.
• Surface smearing and scoring marks at overhaul: A sign of insufficient lubrication or contamination.

None of these signs is a definite diagnosis on its own; but when they appear together, a detailed inspection focused on the eccentric and bushing group is required.

Main Causes of Failure

In eccentric and eccentric bushing failures, the root cause is usually not weak material but deteriorated operating conditions. The following causes stand out:

• Oil contamination: Dust, fine metal particles, water or an unsuitable oil mixture breaks down the oil film and has an abrasive effect on the bushing surface.
• Insufficient oil flow: Low flow, a blocked line, wrong filter selection, a pump problem or the wrong viscosity can leave the bushing surface underfed.
• Cold starting: If load is applied before the oil reaches operating condition, the oil film forms late and the surfaces are strained.
• Overload: Unbalanced feeding, tramp metal, an excessively tight setting or forcing capacity increases bushing load.
• Wrong tolerances and clearance: An over-tight fit, incorrect machining or an out-of-dimension aftermarket part directly affects the oil film.
• Incorrect assembly: The bushing not seating fully, a dirty bore, misalignment or an unsuitable heating/cooling method can cause damage in a short time.

In cone crushers, lubrication, setting and load management must be handled as a whole. An eccentric bushing failure is therefore in most cases an indicator of the maintenance discipline of the whole system rather than of a single part.

Inspection and Measurement: When and How?

Because the eccentric and bushing group usually works inside a closed housing, listening to the noise or looking from outside is not enough for a sound assessment. The right approach is to combine online monitoring with mechanical measurement during overhaul.

Indicators to monitor in operation

• Oil supply and return temperature trend,
• Oil pressure and flow stability,
• Filter differential pressure or clogging indicators,
• Wear metal trend in oil analysis,
• Changes in noise and vibration.

Mechanical checks during overhaul

• Clearance measurement: The clearance between the bushing and shaft or related running surface must be measured using the method in the manufacturer’s manual.
• Surface inspection: Examine for smearing, scoring, local burn marks, discoloration and cracks.
• Seating check: Check whether the bushing is fully seated in the eccentric and whether there are signs of loosening or rotation.
• Geometric check: Ovality, taper, misalignment and surface flatness are assessed.

The critical point here is this: exact acceptance and rejection limits vary by machine model. The manufacturer’s manual and technical drawings must therefore be the basis for clearance, interference, surface tolerance and assembly method.

What to Watch in Periodic Maintenance

The most effective way to extend eccentric bushing life is not to react after a failure but to manage lubrication and load conditions with discipline.

• Keep the oil clean: The tank, lines, filters and seals must be clean and working.
• Bring the oil to operating condition before loading: Especially in cold weather, full load should not be applied before the oil reaches its working condition.
• Do not delay filter changes: A clogged filter can cause loss of flow and bypass operation.
• Keep the feed balanced: Intermittent or one-sided feeding can disturb bushing load distribution.
• Do not neglect tramp metal protection: Overload impacts can start sudden damage on the bushing surface.
• Record overhaul measurements: The clearance and surface condition measured at each maintenance should be kept as a trend.

When a new or overhauled crusher is put into service, early checks are especially important. Temperature trend, noise, oil cleanliness and load behaviour should be monitored closely.

Repair or Replace?

Not every sign of wear in the eccentric group means complete replacement; but where bushings are concerned, the decision must be made carefully. If damage is limited to superficial marks and dimensions are still within acceptance limits, the part can be reused after controlled cleaning and maintenance of the related systems. On the other hand, replacement is the right choice in the following cases:

• Clearance exceeds the manufacturer’s limit,
• The surface shows smearing, scoring or loss of material over a large area,
• There are rotation marks or loosening of the bushing in its bore,
• Oil analysis repeatedly shows an increase in bronze wear metals,
• The mating shaft or bearing surface is also damaged.

If there is geometric distortion in the eccentric body, bore surface or main shaft, replacing only the bushing does not give a permanent solution. In that case all mating surfaces must be assessed together.

Eccentric Bushing Replacement: Step by Step

The sequence below gives the general site logic. However, the manufacturer’s manual must always be followed for removal tools, lifting points, heating method, interference values and final clearance verification.

1. Planning and safety preparation: Work order, lifting plan, spare part conformity, measuring equipment and LOTO preparation are completed.
2. Stopping the machine safely: Feed is stopped, the crusher is emptied, all energy sources are isolated and the oil system and auxiliary equipment are made safe.
3. Marking before disassembly: Orientation of mating parts, shims, adjustment parts and position references are marked.
4. Removing the eccentric group: The group is removed in a controlled way with suitable lifting equipment and tools. Removal by impact is avoided.
5. Removing the old bushing: Depending on the design, the bushing is removed by pressing, controlled heating or the special method described by the manufacturer. Cutting, random tack welding or excessive flame can damage the bore.
6. Cleaning and inspecting the bore: The inner surface of the eccentric is cleaned completely and checked for scoring, cracks, ovality, rotation marks and seating defects.
7. Verifying the new bushing: Part number, material, dimensions, oil groove direction, machining quality and certificate are checked.
8. Preparing for assembly: If an interference fit is used, the appropriate temperature difference and assembly procedure are prepared as described by the manufacturer. In designs using a poured backing or liquid wedge, mixing, surface preparation and curing times are followed exactly. CSP Mühendislik supplies Aurox eccentric liquid wedge for this purpose.
9. Seating the bushing: The bushing is seated in the eccentric in the correct orientation and exactly on axis. Alignment of oil holes and grooves is checked.
10. Final measurements: Bore diameter, seating, alignment and running clearance are verified. If necessary, the mating shaft/surface is also measured.
11. Assembly and initial lubrication: The group is reassembled, the oil circuit is prepared with clean oil and the pre-lubrication or circulation procedure is applied.
12. Controlled commissioning: Initially run at low load while temperature, pressure, noise and oil return are closely monitored.

The two most critical points in this job are correct seating and correct clearance. If the bushing is poorly seated in the eccentric, heat transfer is impaired, the risk of rotation increases and the oil film becomes unstable. If the clearance is wrong, either excessive friction or knocking under load will occur.

Common Mistakes

• Replacing only the bushing: If the mating surface is damaged, the new bushing will wear again quickly.
• Assembling without solving oil contamination: The failure repeats because the root cause has not been removed.
• Using an aftermarket part without measuring it: Even if it seems to fit externally, the tolerances, oil groove layout or alloy may differ.
• Continuing the habit of cold starting: Causes early damage to the newly fitted bushing.
• Assembling with excessive heat: The bushing material and dimensional tolerances can be impaired.
• Skipping oil groove alignment: One of the most critical assembly mistakes.
• Not keeping measurement records: Without a visible trend, work is done after failures rather than as planned overhauls.

What to Watch When Selecting and Buying Spare Parts

From the outside, an eccentric bushing may look like a simple cylindrical part; in reality it is a precision part in terms of geometry, alloy, surface finish and lubrication details. The purchasing decision should therefore be based on technical suitability, not price alone.

OEM versus aftermarket

An OEM part offers the least uncertainty regarding the machine’s design tolerances and material structure. An aftermarket part can be used when produced with proper engineering and quality control; but external dimensional similarity alone is not enough. When choosing an aftermarket part, always ask about:

• Part number and revision compatibility,
• Material composition and thermal/metallurgical suitability,
• Inside and outside diameters, length, groove and shoulder geometry,
• Tolerances and surface roughness,
• Oil groove direction and cross-sections,
• Certificate, dimensional report and traceability.

Material selection

Bronze-based alloys are mostly preferred for eccentric bushings because they offer suitable embeddability, load-carrying capacity and oil-film behaviour in plain bearing applications. However, “bronze” alone is not a sufficient description. The type of alloy must suit the working load and the design. Ask the seller for at least the material designation and, if possible, chemical analysis/certificate information.

Dimensions and tolerances

This is the most critical issue for an eccentric bushing. Even a very small tolerance deviation can change the behaviour of the oil film. Always ask:

• To which drawing or sample was the part manufactured?
• Is there a final inspection report?
• Were the inside and outside diameters machined on the same axis?
• How will the target clearance be verified after assembly?

Certificates and quality documents

The aim here is traceability, not formality. At minimum, a material certificate, a dimensional inspection report and the ability to identify the batch are important. Incoming quality inspection before assembly is particularly beneficial for plants that manage critical stock.

When sourcing, do not limit the scope to the bushing alone. Considering mating surfaces, gaskets, seals and other related components together with the product groups on the Cone Crusher Spare Parts page makes the maintenance plan more robust.

Safety: LOTO and Safe Intervention

Working on the eccentric group requires not only mechanical skill but strict safety discipline. Cone crushers can involve electrical, hydraulic, rotating mechanical, stored energy and lifting risks all at once. The LOTO (lockout-tagout) procedure is therefore indispensable.

• Isolate electrical energy: The main motor, lubrication unit, heaters and auxiliary systems must be locked out.
• Make hydraulic and pressurised circuits safe: Pressure must be fully released and the possibility of re-energisation prevented.
• Confirm rotating parts have stopped: Check for free rotation or residual movement.
• Ensure suspended load safety: Lifting equipment must be of suitable capacity, with approved slings and lugs.
• Manage hot work risks: Take fire and burn precautions for assemblies that require heating.
• Control oil and chemical exposure: Prevent spills and use suitable gloves and eye protection.

LOTO is not just switching off the main isolator. Do not start disassembly until it is verified that the energy is cut, pressure is released, the equipment cannot be started accidentally and the work area is safe.

Frequently Asked Questions

How often is the eccentric bushing replaced?

It is not right to give a fixed period. Life depends on feed characteristics, load, oil cleanliness, operator habits and part quality. The soundest approach is to decide based on temperature trends, oil analysis and overhaul measurements.

Does copper in oil analysis always mean a bushing failure?

It usually suggests wear of bronze-based surfaces, but it is not a definite diagnosis on its own. The sampling method, the presence of other bronze parts and trend analysis must be evaluated together.

Should the crusher be stopped immediately when metallic noise is heard?

If high-risk metallic noise, knocking or rising temperature appear together, the crusher should not be forced and a safe stop should be planned. Running like this for a long time can damage the main shaft and eccentric body.

Is it enough to replace only the bushing and carry on?

Only if the mating surfaces are sound and the bore tolerances are acceptable. If the main shaft, eccentric bore or oil grooves are faulty, replacing the bushing alone is not a permanent solution.

Can an aftermarket part be used?

Yes, but only with the right material, correct tolerances, correct oil groove layout and traceable quality control. Otherwise a short-term price advantage can turn into a much greater failure cost.

Which checks are the priority after assembly?

During the first run, oil flow, oil return temperature, noise, leaks and stable load behaviour should be monitored first. The manufacturer’s manual is the basis for the exact monitoring plan.

Spare Parts and Service for the Cone Crusher Eccentric and Eccentric Bushing

Based in Ankara, CSP Mühendislik provides support for CONE CRUSHERS and their critical components in crushing, screening and mining equipment. For the cone crusher eccentric and eccentric bushing group, correct part matching, dimensional verification, overhaul planning and site application are as important as the part itself.

In this context, in addition to supplying Cone Crusher Spare Parts, CSP Mühendislik provides service, maintenance and repair support for disassembly, inspection, maintenance, overhaul and commissioning. If needed, you can talk to the technical team via the Contact page about part suitability, overhaul scope or an on-site inspection.

In summary, the eccentric and eccentric bushing group is a node that looks small but directly determines crusher life. When correct lubrication, correct measurement, correct assembly and correct spare parts come together, the risk of unplanned downtime is significantly reduced.