Pins and bushings are small compared with an excavator's engine or hydraulic system, but worn linkage joints can affect digging accuracy, bucket control and repair cost. Before buying a used excavator, check the pivot points around the bucket, linkage, arm and boom instead of judging the machine only from operating hours or exterior appearance.
Start by watching how the bucket and front attachment move. Look for excessive play, knocking, uneven movement, damaged retainers and poor lubrication. Then inspect the pins, grease fittings, seals and surrounding bosses. A small amount of movement may be normal depending on the machine, but obvious looseness or metal-to-metal movement deserves further investigation. Exact acceptable clearances vary by manufacturer, model and joint, so any serious wear should be compared with the correct service specification before purchase.
Which Pins and Bushings Should You Check?
An excavator front attachment contains several pivot joints.
Depending on the machine design, important areas can include:
- Boom-to-upper-structure pivot
- Boom cylinder pin joints
- Boom-to-arm joint
- Arm cylinder pin joints
- Bucket cylinder joints
- Bucket-to-arm pivot
- Bucket linkage pins
- Quick coupler pins where fitted
Each joint uses pins and bearing or bushing surfaces to allow controlled movement under heavy load.
Specifications vary by model year and configuration. Exact specifications should be confirmed for each individual machine.
Why Pins and Bushings Wear
These joints carry repeated digging, lifting and impact loads.
Wear can increase because of:
- Insufficient lubrication
- Dirt and abrasive material
- Water contamination
- Misalignment
- Heavy breaker or demolition use
- Damaged seals
- Worn pins
- Worn bushings
- Incorrect replacement parts
Caterpillar identifies poor lubrication, dirt, debris and misalignment as important causes of accelerated linkage wear.
Start With the Bucket Linkage
The bucket linkage is one of the easiest areas to inspect because it moves through a large range during normal operation.
Watch the bucket while the operator slowly curls and uncurls it.
Look for:
- Sudden movement before the bucket responds
- Visible gap changes around pins
- Knocking sounds
- Side-to-side movement
- Loose linkage plates
- Movement between pin and structure
A worn bucket linkage can make precise grading or loading more difficult.
Check for Vertical and Side Play
Pin wear does not always appear in only one direction.
Look for both:
- Vertical movement
- Side-to-side movement
Excessive movement can come from:
- Worn pin
- Worn bushing
- Missing or worn shims
- Worn thrust surfaces
- Damaged linkage structure
Do not assume the bushing alone is the problem.
Movement at the Pin and Movement of the Whole Joint Are Different
Watch carefully where the movement occurs.
If the complete linkage moves together, the play may come from another joint.
If the pin visibly moves inside the boss or linkage plate, local wear may be present.
Video from a close side angle can help an overseas buyer identify where the movement begins.
Inspect the Pin Retainers
Pins need to remain correctly positioned inside the joint.
Check:
- Keeper plates
- Retaining bolts
- Washers
- Snap rings where used
- Locking hardware
Missing, bent or loose retaining parts can allow unwanted pin movement.
This can increase wear on the surrounding structure.
Look for Pin Rotation Where It Should Not Occur
Depending on joint design, the pin may be intended to remain fixed while the bushing rotates around it, or the joint may use another arrangement.
If a pin visibly rotates or moves inside a boss where it should remain fixed, inspect the retaining system and boss condition carefully.
Do not apply one design assumption to every excavator.
Inspect Grease Around the Joint
Grease condition provides useful clues about maintenance.
Look for:
- Fresh grease
- Dry joints
- Old hardened grease
- Grease mixed with dirt
- Rust around the pin
- No visible grease at frequently serviced joints
Fresh grease before sale does not prove a long history of correct lubrication.
It only shows the current condition.
Check the Grease Fittings
Inspect each visible grease nipple or fitting.
Look for:
- Broken fittings
- Missing fittings
- Blocked fittings
- Damaged grease lines
- Loose fittings
Hitachi Construction Machinery advises that if grease cannot enter a lubrication point, the grease passage may be blocked.
A joint that has been difficult to grease for a long time may have experienced accelerated wear.
Check Automatic Lubrication Lines Where Fitted
Some larger excavators can use automatic lubrication systems.
If the machine has autolube, inspect:
- Grease lines
- Damaged tubes
- Loose fittings
- Empty reservoir
- Blocked lines
- Visible grease delivery at joints
An autolube system does not guarantee that every joint has received grease correctly.
Listen for Squeaking or Grinding
Caterpillar specifically recommends listening for unusual joint sounds during operation.
Possible warning sounds include:
- Squeaking
- Grinding
- Knocking
- Metallic clicking
A dry joint can create noise, but unusual sound can also come from worn linkage, hydraulic cylinders or other components.
Use sound as one clue, not as a complete diagnosis.
Inspect the Pin Surface Where Visible
Part of the pin surface may be visible at the ends of the joint.
Look for:
- Rust
- Scoring
- Grooves
- Galling
- Cracks
- Impact damage
Caterpillar identifies grooves, galling and visible damage as signs that a linkage pin may require replacement.
What Is Galling?
Galling is severe surface damage caused by friction between contacting metal surfaces.
Caterpillar notes that insufficient lubrication can contribute to pin galling and seizure.
If heavy galling is visible, the buyer should consider more than simply adding grease.
The pin, bushing and surrounding joint may need repair.
Inspect the Bushing Area
The bushing itself may not be fully visible while installed.
However, possible signs of bushing wear include:
- Excessive joint play
- Uneven pin position
- Metal debris
- Abnormal noise
- Difficulty holding alignment
If wear appears significant, accurate inspection may require pin removal or measurement by a technician.
Do Not Confuse Bushing Wear With Boss Wear
This distinction can have a major effect on repair cost.
The bushing is designed as a replaceable wear component on many joints.
However, if wear continues for too long, the surrounding bore or boss can also become worn.
This may require:
- Line boring
- Welding and machining
- Bore repair
- Structural repair
Therefore, heavy joint play deserves closer inspection before purchase.
Check for Previous Line-Boring Repairs
Previous bore repair is not automatically a problem.
A correctly completed repair can restore alignment.
However, look for:
- Visible weld repair around bosses
- Uneven machining
- Misalignment
- Unusual pin fit
- Cracks around repaired areas
If documentation is available, ask what repair was performed and when.
Check Shims and Side Clearance
Excavator bucket and linkage joints can use shims or spacers to control side clearance.
Inspect for:
- Missing shims
- Damaged shims
- Excessive side gap
- Uneven spacing
Caterpillar describes linkage shims and spacers as components that help maintain correct spacing and alignment and reduce premature pin and bushing wear.
Inspect the Bucket-to-Arm Joint
This joint receives high digging loads and deserves close attention.
Check:
- Pin movement
- Bushing play
- Boss condition
- Grease condition
- Retainer condition
- Side clearance
If the excavator has worked with heavy buckets or attachments, wear may be greater.
Inspect the Bucket Cylinder Joint
The bucket cylinder applies force through the linkage.
Inspect the pins at both ends of the cylinder where accessible.
Look for:
- Movement between pin and bushing
- Damaged pin retainers
- Dry grease points
- Wear around the cylinder eye
Do not confuse cylinder-eye movement with hydraulic cylinder seal leakage. They are separate issues.
Check the Arm-to-Boom Joint
The boom-to-arm pivot carries major digging and lifting forces.
Look for:
- Side movement
- Vertical play
- Pin retainer condition
- Grease distribution
- Cracks around the joint
- Previous repair
This joint can be harder to judge from a short video, so close-up footage may be useful.
Check the Boom Foot Pin
The boom foot connects the front attachment to the excavator upper structure.
Wear here can affect the movement of the entire front attachment.
Inspect:
- Visible movement
- Pin retention
- Grease condition
- Boss condition
- Cracks
Repair access and cost may be different from a bucket linkage repair.
Check Quick Coupler Pins Where Fitted
If the excavator has a mechanical or hydraulic quick coupler, inspect its pivot and locking components separately.
Look for:
- Pin wear
- Loose joints
- Damaged locking components
- Excessive clearance
- Cracks
The coupler should also be checked according to the coupler manufacturer's requirements.
Attachments Can Accelerate Wear
Previous attachment use matters.
| Previous Use | Pin and Bushing Areas to Check Closely |
|---|---|
| General digging | Bucket pivot and bucket linkage |
| Hydraulic breaker | Boom-to-arm, bucket end and attachment joints |
| Demolition crusher | Front linkage, bucket cylinder joints and boom/arm pivots |
| Large heavy bucket | Bucket pin, linkage and arm end |
| Rental fleet | All grease points and repair history |
| Sand or abrasive environment | Seals, grease condition and exposed joint surfaces |
If previous attachment use cannot be confirmed, treat it as unknown.
Operating Hours Alone Cannot Tell You Linkage Wear
Two excavators with the same operating hours can have very different pin and bushing condition.
Wear depends on:
- Lubrication frequency
- Attachment type
- Material being excavated
- Operator technique
- Contamination
- Joint loading
- Repair history
Hours provide context, but actual joint movement tells you more about current condition.
A Low-Hour Machine Can Still Have Loose Linkage
Heavy hammering, demolition or poor lubrication can create wear quickly.
Conversely, a higher-hour excavator may have had pins and bushings replaced during its service life.
This is why a buyer should inspect the current linkage rather than trying to estimate wear from hours alone.
Ask Whether Pins or Bushings Have Been Replaced
If maintenance information is available, ask about:
- Bucket pin replacement
- Bucket bushing replacement
- Linkage repair
- Boom pin replacement
- Arm pin replacement
- Line boring
- Autolube repair
Recently replaced pins and bushings can be positive if the repair was completed correctly.
New Pins Do Not Automatically Mean the Joint Is Repaired
If a worn bore remains oversized, installing a new pin alone may not remove the play.
Likewise, replacing only a bushing may not solve wear in the surrounding structure.
After a reported repair, check actual joint movement again.
Can You Measure Pin and Bushing Wear?
Yes, but the correct method depends on the joint and manufacturer.
A technician may check:
- Pin diameter
- Bushing inside diameter
- Joint clearance
- Side clearance
- Bore alignment
Do not use a generic maximum-clearance figure for every excavator.
Compare measurements with the correct service information for the exact model.
Simple Field Tests Can Reveal Play
Without dismantling the joint, controlled machine movement can reveal excessive play.
An operator can slowly load and unload the linkage while an observer watches from a safe location.
Useful movements may include:
- Slow bucket curl
- Bucket contact with the ground
- Small boom movements
- Small arm movements
No person should stand inside a pinch zone or beneath raised equipment.
Watch One Joint at a Time
If several joints move at once, it becomes difficult to identify the source of play.
Ask the operator to move the machine slowly.
Focus on:
- Bucket-to-arm joint
- Bucket linkage
- Bucket cylinder connection
- Boom-to-arm joint
- Boom foot
This makes visual diagnosis much easier.
Excessive Play Can Affect More Than Accuracy
Loose linkage can contribute to:
- Reduced bucket control
- Knocking during digging
- Accelerated wear
- Seal damage
- Misalignment
- Higher repair cost
The impact depends on which joint is worn and how severe the wear has become.
Look for Cracks Around Pin Bosses
Heavy loading and prolonged joint looseness can place additional stress on surrounding structures.
Inspect around:
- Bucket bosses
- Arm end
- Linkage plates
- Boom joint areas
Hitachi Construction Machinery specifically includes boom, arm and linkage cracks, deformation and damage in its recommended daily inspection areas.
Do Not Ignore Seals Around Pins
Some joints use seals to keep grease in and contaminants out.
Inspect for:
- Torn seals
- Missing seals
- Grease escaping unevenly
- Dirt entering the joint
Komatsu notes that properly functioning pin seals help retain grease between pins and bushings while limiting dirt and dust entry.
Greasing Frequency Depends on the Machine
Do not assume every excavator requires the same lubrication interval.
Caterpillar advises checking the machine's Operation and Maintenance Manual for the correct grease locations and intervals.
Some designs can have extended lubrication intervals.
For example, Hitachi has used HN bushings on certain excavators to increase grease retention and extend lubrication intervals.
Use the exact model's maintenance information.
Common Pin and Bushing Red Flags
- Obvious bucket linkage slop
- Large side movement
- Heavy knocking
- Squeaking or grinding
- Dry joints
- Blocked grease fittings
- Broken grease lines
- Grooved or galled pins
- Missing pin retainers
- Visible boss movement
- Cracks around linkage joints
- Heavy previous weld or line-bore repair with unclear history
One red flag does not automatically mean the excavator is unsuitable.
The buyer should understand the repair scope and cost before deciding.
A Practical Pins and Bushings Inspection Checklist
- Bucket Pivot: Check movement, grease and pin retention.
- Bucket Linkage: Look for play and knocking.
- Bucket Cylinder Pins: Inspect both pivot points.
- Boom-to-Arm Joint: Check vertical and side movement.
- Boom Foot: Inspect play and surrounding structure.
- Quick Coupler: Check pins and locking components where fitted.
- Grease Fittings: Look for broken or blocked fittings.
- Autolube: Inspect lines and grease delivery where fitted.
- Pin Surface: Look for grooves, galling, rust and cracks.
- Bushing Wear: Watch for excessive joint movement.
- Shims: Check side clearance and missing spacers.
- Retainers: Inspect plates, bolts, washers and rings.
- Bosses: Look for cracks, movement and repair.
- Noise: Listen for squeaking, grinding and knocking.
- Maintenance: Ask about lubrication and previous repairs.
- Attachments: Consider previous breaker or demolition use.
- Hours: Compare operating hours with actual linkage condition.
- Measurements: Use model-specific clearance limits where needed.
What Should an Overseas Buyer Request?
If you cannot inspect the excavator personally in Japan, request focused photos and videos.
Useful material includes:
- Close video of bucket linkage movement
- Bucket-to-arm pin close-up
- Boom-to-arm joint video
- Boom foot close-up
- Grease fitting photos
- Pin retainer photos
- Photos of visible repairs around bosses
- Slow bucket curl video
A wide machine-operation video may hide small joint movement.
Close-up footage is much more useful for this inspection.
Buying a Used Excavator from Japan
Japanese used machinery can include excavators of many sizes, manufacturers and attachment configurations.
You can check current Japanese used machinery available at EVERYCAR.jp. Inventory changes regularly, so a specific excavator model should not be assumed to remain available.
For more information about checking engines, hydraulic systems, undercarriages and other major areas before purchase, visit the Japanese Used Machinery & Heavy Equipment Guide.
Check the Movement Before Judging the Joint
The most useful pins-and-bushings inspection starts by watching how each joint moves.
Check bucket linkage play first. Then move upward through the bucket cylinder, boom-to-arm joint and boom foot. Look at grease condition, retainers, pin surfaces, shims and surrounding bosses.
If the movement appears excessive, do not guess a remaining-life percentage. Confirm the source of the play and compare measurements with the correct service specification.
If you are looking for a used excavator from Japan, you can contact EVERY with your preferred manufacturer, model, size, budget and destination. Exact linkage condition, repair history and machine specification should be confirmed for each individual excavator before purchase.
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