Hitachi 4648390 ZX900-6A undercarriage Track Roller Assembly/Heavy-duty excavator chassis coponents manufacture and source factory-DPW Parts
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Product Specifications
Technical Specification: Hitachi Part #4648390 - Track Roller Assembly for ZX900-6A
This assembly is a critical load-bearing component within the undercarriage system of the 90-ton class Hitachi ZX900-6A excavator. Its design is optimized for severe duty cycles in mining, heavy construction, and quarry applications.
1. Primary Function and Application
Machine Model: Hitachi ZX900-6A (and likely compatible variants within the ZX900 series).
Component Identity: Track Roller (also commonly called Bottom Roller or Lower Roller).
Primary Functions:
Load Support: To carry the substantial weight of the excavator (approx. 90 tons) and distribute it through the track chain to the ground.
Track Guidance: The roller's flanges run against the track links, maintaining lateral alignment and preventing derailment from the sprocket and idler.
Stability: Contributes to the machine's overall stability during stationary work and travel.
2. Key Engineering Features and Design Specifications
The part number 4648390 represents a complete, ready-to-install assembly. Its design incorporates heavy-duty features to withstand high impact loads and abrasive environments.
| Feature | Technical Description |
|---|---|
| Type | Sealed and Lubricated Track Roller (Lube-in-Long-Life design). |
| Flange Design | Double-Flange. This is the standard configuration for most lower rollers, providing positive guidance on both sides of the track link. |
| Mounting | The internal shaft is pressed and/or bolted directly into the track frame or a bogie assembly. The roller shell rotates around this stationary shaft. |
| Internal Construction | Utilizes sleeve bushings (typically oil-impregnated sintered bronze) that rotate on the hardened stationary shaft. This design prioritizes high load capacity and durability over low friction. |
| Sealing System | Critical Component. Employs a multi-stage seal, almost certainly a Duo-Cone seal system. This consists of two precision-machined metal rings that form a labyrinth seal, effective at keeping grease in and abrasive contaminants out. |
| Lubrication | Pre-packed with high-temperature, high-pressure grease. A single grease fitting (Zerk fitting) is provided for periodic replenishment during maintenance. |
3. Common Part Number Context
OEM Part Number: 4648390 is the definitive Hitachi manufacturer's part number. Always use this number when ordering from an authorized Hitachi dealer to ensure perfect compatibility.
Aftermarket Equivalents: Major undercarriage manufacturers like DPW Parts produce equivalent assemblies. They will have their own cross-reference part numbers (e.g., a common equivalent might be ). It is crucial to confirm the cross-reference with the supplier.
4. Common Failure Modes
Failure of this roller follows typical patterns for heavy-duty undercarriage components:
Flange Wear: Progressive wear on the guiding flanges reduces their height, compromising track alignment and increasing the risk of derailment.
Seal Failure: The primary failure initiator. If the Duo-Cone seals are damaged, abrasive contaminants (dust, silt) enter the assembly. This leads to rapid wear of the bushings and shaft.
Roller Seizure: Caused by severe contamination or lubrication loss. The roller stops turning and is ground flat by the track link, causing accelerated, catastrophic wear to both the roller and the track chain.
Excessive Play: Worn internal bushings and shaft create radial (up-down) and axial (side-to-side) looseness. This results in noisy operation, erratic track movement, and increased stress on other undercarriage components.
Cracking/Breakage: Impact with sharp rock ledges or rebar can cause structural cracks in the roller shell or flanges.
5. Maintenance and Replacement Best Practices
Inspection: Perform daily walk-around inspections. Look for rollers that are not spinning, show signs of grease leakage, or have visibly worn or damaged flanges.
Lubrication: Follow Hitachi's recommended service intervals for lubricating the track rollers. Use the specified grease type.
Cleaning: Keep the undercarriage as clean as possible. Packed debris increases operating temperature and accelerates seal and flange wear.
Track Tension: Maintain correct track tension as per the operator's manual. Incorrect tension is a major contributor to premature roller and track failure.
Replacement Strategy: For optimal performance and balanced wear, replace track rollers in matched sets on the same side of the machine. Replacing a single roller on a side with other worn rollers will lead to uneven load distribution and rapid failure of the new part.
