| Parameter | Specification | Testing Standard |
|---|---|---|
| COGENG Part Number | COGENG-707-98-25090-BM | Internal Quality Standard QS-521 |
| Replaces OEM Part No. | Komatsu 707-98-25090 | Direct OEM Replacement |
| Piston Seal Material | Polyurethane (PU) Grade 95A | ISO 6072 |
| Rod Seal Material | Nitrile (NBR) with PTFE fill | ISO 6072 |
| Wiper Material | Polyurethane double-lipped | ISO 6194 |
| O-Ring Material | Nitrile (NBR) 70 Durometer | ISO 3601-1 |
| Wear Band Material | PTFE-filled composite | ISO 6811 |
| Backup Ring Material | Nylon 6.6 | ISO 1874-1 |
| Temperature Range | -40°C to +110°C (-40°F to +230°F) | ISO 2230 |
| Pressure Rating | Up to 32 MPa (4640 PSI) | ISO 10766-1 |
| Fluid Compatibility | Komatsu Super Hydraulic Fluid, mineral oil, synthetic | ISO 6743-4 |
| Shelf Life | 5 years in original packaging | ISO 2230 |
| Component | Material | Size Specification | Quantity | Function |
|---|---|---|---|---|
| Main Piston Seal | Polyurethane | 120mm ID x 9mm width | 1 | Primary pressure sealing |
| Rod Seal | NBR with PTFE | 85mm ID x 7mm width | 1 | Dynamic rod sealing |
| Buffer Seal | Polyurethane | 120mm ID x 7mm width | 1 | Pressure peak protection |
| Wiper Seal | Polyurethane double-lipped | 85.5mm ID | 1 | Contaminant exclusion |
| Wear Bands | PTFE composite | 120mm OD x 7mm width | 2 | Piston guidance |
| O-Rings | Nitrile (NBR) | Various sizes AS568 | 7 | Static sealing |
| Backup Rings | Nylon 6.6 | Various sizes | 4 | Anti-extrusion support |
| Guide Rings | PTFE-filled fabric | 120mm OD x 7mm width | 2 | Bearing surface protection |
| Gland Gasket | NBR | 90mm OD x 3mm CS | 1 | Gland static seal |
| Manufacturer | Model Series | Specific Models | Year Range | Application |
|---|---|---|---|---|
| Komatsu | WB140-2 | WB140-2 Standard | 1998-2002 | Backhoe Boom Cylinder |
| Komatsu | WB140-2 | WB140-2N, WB140-2E | 1999-2003 | Main Lift Cylinder |
| Komatsu | WB140 Series | WB140-2S, WB140-2H | 2000-2004 | Excavation Boom |
| Related Models | WB140 Series | WB140-1, WB140-3 | 1997-2001 | Verify compatibility |
| Parameter | Specification | Tolerance | Application |
|---|---|---|---|
| Cylinder Bore | 120 mm | +0.12/-0.00 mm | Boom cylinder |
| Piston Rod Diameter | 85 mm | +0.00/-0.06 mm | Chrome-plated rod |
| Stroke Length | 1,150 mm | ±4 mm | Boom lift range |
| Rod Finish | Hard chrome plated | Ra 0.2-0.4 μm | Surface roughness |
| Operating Pressure | 27.4 MPa (280 kg/cm²) | ±2% | System design pressure |
| Lifting Capacity | 3,500 kg @ full extension | ±5% | Maximum boom load |
| Breakout Force | 9,800 kgf | ±5% | Digging force capacity |
| NO | Number | Name | Qty |
| KIT | 707-98-25090 | SERVICE KIT, LIFT | 2 |
| CYL | 707-00-80C10 | CYLINDER ASSY, LIFT | 2 |
| 1 | 721-11-80500 | • CYLINDER | 1 |
| 2 | 07144-10505 | • BUSHING | 1 |
| 3 | 707-29-80740 | • HEAD, CYLINDER | 1 |
| 4 | 07177-05030 | • BUSHING | 1 |
| 5 | 707-51-50211 | • PACKING, ROD (KIT) | 1 |
| 6 | 176-63-92240 | • SEAL, DUST (KIT) | 1 |
| 7 | 07179-12062 | • RING, SNAP | 1 |
| 8 | 07000-12080 | • O-RING (KIT) | 1 |
| 9 | 07146-02076 | • RING, BACK-UP (KIT) | 1 |
| 10 | 07000-12075 | • O-RING (KIT) | 1 |
| 11 | 721-58-50961 | • ROD, PISTON | 1 |
| 12 | 707-76-45550 | • BUSHING | 1 |
| 13 | 707-36-80370 | • PISTON | 1 |
| 14 | 707-44-80180 | • RING, PISTON (KIT) | 1 |
| 15 | 07156-00810 | • RING, WEAR | 1 |
| 16 | 01580-03629 | • NUT | 1 |
| Performance Parameter | Value | Test Method |
|---|---|---|
| Seal Life Expectancy | 3,500 operating hours | ISO 7983 |
| Friction Coefficient | 0.07-0.11 | ASTM D1894 |
| Extrusion Resistance | 35 MPa sustained | ISO 1829 |
| Compression Set | <13% after 24h @ 100°C | ISO 815 |
| Abrasion Resistance | >55,000 cycles | ISO 4649 |
| Low Temp Performance | -40°C operational | ISO 2929 |
1. What is a backhoe boom cylinder, and what does this kit seal?
The backhoe boom cylinder is the large hydraulic cylinder that raises and lowers the main boom arm on the backhoe side of the Komatsu WB140-2 backhoe loader. This cylinder bears the highest structural loads on the backhoe — responsible for lifting, digging, and craning operations. This kit provides all seals required to completely overhaul one boom cylinder.
2. Is this kit specifically for the Komatsu WB140-2 only?
Yes. This kit under Part No. 707-98-25090 is specifically engineered for the Komatsu WB140-2 backhoe loader. The WB140-2 is a distinct model in Komatsu's backhoe loader line, with its own cylinder specifications. It is not automatically compatible with:
Other WB series models (e.g., WB93, WB97, WB150)
Later WB140 variants (e.g., WB140-3, WB140-5) without explicit confirmation
The loader-side cylinders on the same machine
Always verify using the OEM cylinder number stamped on your boom cylinder.
3. Is this one kit per cylinder?
Yes. Each kit is for one single boom cylinder. The WB140-2 backhoe typically uses one boom cylinder (single cylinder design), so one kit is generally sufficient for a complete boom cylinder rebuild. However, always physically confirm your machine's cylinder count — some configurations or regional variants may differ.
4. What does "Premium" and "Direct OEM Replacement" mean for this kit?
Premium: Indicates this kit is manufactured with enhanced material formulations and tighter quality controls compared to standard aftermarket alternatives. It is built to withstand the severe digging, shock-loading, and high-duty-cycle demands of backhoe boom operations.
Direct OEM Replacement: All seals are dimensionally precise drop-in replacements for the genuine Komatsu seals. No modifications to seal grooves, gland, or piston are required. Seal profiles, stack heights, and material specifications match OEM design.
This is a COGENG aftermarket product, not a genuine Komatsu part.
5. What is included in the "Complete Hydraulic Repair" kit?
One kit contains all soft sealing components for a full single-cylinder rebuild:
Piston seal assembly – High-pressure primary seal for the piston, designed for bidirectional loading (boom raise and lower under load)
Rod seal – Primary seal at the gland for the large-diameter boom cylinder rod
Buffer ring – Pressure transient protection, critical for absorbing shock loads during digging and breakout operations
Dust wiper / scraper – Heavy-duty exclusion seal; protects against dirt, dust, and moisture entry — especially important for the exposed boom cylinder on a backhoe working in trenches
Wear rings / guide bands – Piston and rod gland guidance rings, formulated to resist the extreme side-loading inherent in backhoe digging
Static O-rings and backup rings – For the gland-to-barrel interface, piston lock nut, and cylinder head/end cap
Additional ancillary seals – As required by the specific WB140-2 boom cylinder architecture
6. What are the operating specifications?
Pressure rating: Up to 35 MPa (5,075 PSI) , matching Komatsu WB140-2 backhoe implement circuit pressure
Temperature range: -30°C to +110°C (-22°F to +230°F)
Seal materials: Polyurethane for primary dynamic seals (high tensile strength, abrasion resistance); NBR for O-rings and static seals; composite PTFE or phenolic wear rings for side-load distribution
Fluid compatibility: Standard mineral hydraulic oils (ISO VG 32, 46, 68)
7. Why is the boom cylinder on a backhoe loader particularly demanding on seals?
The backhoe boom cylinder experiences the most aggressive service conditions of any cylinder on the WB140-2:
Extreme side-loading – Digging, particularly with the boom swung to one side, imposes severe bending moments on the rod and piston
High shock loads – Striking rocks, roots, or buried obstructions generates instantaneous pressure spikes far exceeding nominal system pressure
Full extension contamination – When trenching, the cylinder is frequently fully extended with the rod fully exposed to falling dirt, water, and debris
Continuous cycling – Production digging requires hundreds of full-stroke cycles per day, generating heat and material fatigue
The COGENG kit is engineered with these specific stresses in mind.
8. What are the failure symptoms indicating this kit is needed?
Boom drift / sag – Boom slowly lowers with the control lever in neutral, especially with a loaded bucket
Visible rod leakage – Oil seeping past the gland onto the chrome rod during extension and retraction
Weak lifting performance – Boom struggles to lift a full bucket or slows noticeably
Cavitation / aeration – Frothy hydraulic oil or erratic boom movement
External oil accumulation – Oil pooling around the gland nut or cylinder head
Contaminated oil – Milky or discolored hydraulic fluid indicating moisture or dirt ingress
9. How do I confirm fitment for my WB140-2?
Pre-order verification is critical:
Locate the OEM cylinder number stamped on the boom cylinder barrel or gland (707-XX-XXXXX format). This is the definitive reference.
Confirm cylinder function — Ensure it is the backhoe boom cylinder, not the dipper/stick cylinder, bucket cylinder, stabilizer cylinder, or loader-side cylinders.
Provide your machine's full serial number — The WB140-2 may have mid-production updates, regional variants, or accumulated field modifications.
If stampings are illegible — Measure the cylinder rod diameter and bore diameter with precision instruments. The boom cylinder will have the largest rod diameter on the backhoe side.
Check for prior rebuilds — If the cylinder was previously rebuilt with non-OEM parts, internal dimensions may have been altered. Verify groove dimensions against OEM specifications.
10. Is this the same as a WB140-3 or WB150 boom cylinder kit?
No. Different WB series models and generational variants (e.g., WB140-2 vs. WB140-3) often use different cylinder designs with different seal dimensions. Part No. 707-98-25090 is linked to the WB140-2. Never substitute a kit from one model generation into another without explicit dimensional confirmation. Using an incorrect kit will result in immediate seal failure and potential cylinder damage.
11. What installation guidance is provided?
An exploded seal arrangement diagram is included with the kit
Full step-by-step rebuild instructions are not provided; consult the Komatsu WB140-2 Shop Manual for:
Gland nut torque specifications
Piston nut torque values
Bleeding / air purging procedures
Cylinder removal and installation sequences
Critical installation practices for backhoe boom cylinders:
Rod inspection — Thoroughly examine the chrome rod for scoring, pitting, rust, and stone chips. A damaged rod will destroy new seals within hours of operation
Seal groove preparation — Remove all corrosion and burrs from seal grooves before installation
Seal lubrication — Use clean hydraulic oil (not assembly grease) to lubricate all seals during assembly
Torque discipline — Under-torquing the gland or piston nut can cause catastrophic failure; over-torquing can crack the piston or distort seals
Post-rebuild bleeding — Air trapped in a boom cylinder can cause jerky, uncontrolled movement. Cycle slowly at idle until smooth operation is confirmed
12. What is the ordering and delivery information?
This kit is available factory direct from COGENG. When ordering:
Quantity required: Typically 1 kit per boom cylinder (the WB140-2 generally uses one boom cylinder)
Confirm the OEM part number 707-98-25090 against your cylinder before placing the order
Inquire about stock availability, lead times, and shipping terms for your region
Consider ordering companion kits if performing a full backhoe hydraulic overhaul (dipper, bucket, stabilizer cylinders) at the same time
13. What is the shelf life and warranty?
Shelf life: Up to 7 years stored unopened at 5°C–30°C (41°F–86°F), dry, away from direct sunlight and ozone-generating equipment
Warranty: Standard COGENG manufacturing defect warranty applies. Warranty does not cover failures resulting from incorrect fitment, improper installation, contaminated hydraulic oil, or damaged cylinder rods
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