| Parameter |
Specification |
Notes |
| COGENG Part Number |
COGENG-4320996-SK (Each Kit) |
Our internal part number. This listing is for a 2-PC set. |
| Replaces OEM Part No. |
Hitachi 4320996 |
Direct replacement for the boom cylinder. |
| Kit Quantity |
2 Complete Kits |
For servicing both left and right boom cylinders. |
| Seal Type |
Full Repair Kit |
Includes piston seals, rod seals, wiper seals, guide rings, O-rings, and backup rings. |
| Primary Seal Material |
Nitrile Butadiene Rubber (NBR) |
Excellent resistance to standard hydraulic oils (mineral-based), wide temperature range. |
| Wiper Seal Material |
Polyurethane (PU) |
Superior scraping ability to keep out dirt, mud, and moisture. |
| Wear Ring / Guide Band |
PTFE-filled Nylon |
Reduces friction and prevents metal-to-metal contact, extending cylinder life. |
| Temperature Range |
-40°C to +100°C (-40°F to +212°F) |
Suitable for most climatic conditions. |
| Pressure Rating |
Up to 35 MPa (5000 PSI) |
Designed to handle the high-pressure demands of boom operations. |
| Warranty |
3 Months |
Guarantee against manufacturing defects. |
Parts list
| NO |
Number |
Name |
Qty |
| - |
4257930 |
CYLINDER; BOOM (L) |
1 |
| - |
4286744 |
. CYLINDER (PIPELESS) |
1 |
| - |
4286745 |
.. TUBE; CYLINDER ASSEMBLY |
1 |
| - |
409501 |
.. . TUBE; CYLINDER |
1 |
| - |
408816 |
.. . BUSHING; PIN |
1 |
| - |
4286742 |
.. ROD; PISTON ASSEMBLY |
1 |
| - |
409402 |
.. . ROD; PISTON |
1 |
| - |
174403 |
.. . BUSHING |
1 |
| - |
409403 |
.. HEAD; CYLINDER |
1 |
| - |
310304 |
.. BUSHING |
1 |
| - |
271304 |
.. RING; RETAINING |
1 |
| - |
408804 |
.. RING |
1 |
| - |
271309 |
.. PACKING; U-RING |
1 |
| - |
271310 |
.. RING; BACK-UP |
1 |
| - |
409503 |
.. RING; WIPER |
1 |
| - |
408817 |
.. RING; WIPER |
1 |
| - |
A811090 |
.. O-RING |
1 |
| - |
310606 |
.. RING; BACK-UP |
1 |
| - |
408805 |
.. BOLT; SOCKET |
1 |
| - |
408806 |
.. BEARING; CUSHION |
1 |
| - |
408807 |
.. SEAL |
1 |
| 15 |
409106 |
.. PISTON |
1 |
| 16 |
310608 |
.. RING; SEAL ASSEMBLY |
1 |
| 17 |
409107 |
.. RING; BACK-UP |
1 |
| 18 |
310609 |
.. RING |
1 |
| 19 |
310610 |
.. RING |
1 |
| 20 |
326007 |
.. SHIM |
1 |
| 21 |
409108 |
.. NUT |
1 |
| 22 |
310612 |
.. SCREW; SET |
1 |
| 23 |
111818 |
.. BALL; STEEL |
1 |
| 26 |
J75481 |
.. FITTING; GREASE |
1 |
| 39 |
4084578 |
.. SEAL; DUST |
1 |
| 40 |
4065687 |
.. SEAL; DUST |
1 |
| 57 |
408902 |
. PIPE |
1 |
| - |
94-2013 |
.. PLUG |
1 |
| 58 |
409502 |
. PIPE |
1 |
| 58A |
4174541 |
.. PLUG |
1 |
| 58B |
4506418 |
.. . O-RING |
1 |
| 59 |
4509181 |
. O-RING |
1 |
| 60 |
309019 |
. BOLT; SOCKET |
1 |
| 61 |
310310 |
. BOLT; SOCKET |
1 |
| 62 |
409405 |
. BAND |
1 |
| 63 |
310619 |
. BAND |
1 |
| 64 |
408815 |
. BOLT |
1 |
| 65 |
325913 |
. WASHER |
1 |
| 66 |
310312 |
. HOLDER |
1 |
| 67 |
224115 |
. BOLT |
1 |
| 68 |
208516 |
. WASHER; SPRING |
1 |
| 100 |
4320996 |
KIT; SEAL |
1 |
System Depressurization: Before starting, completely release all hydraulic pressure from the system. Lower the boom and bucket to the ground, and safely cycle all control levers to relieve any trapped pressure in the lines.
Work in a Clean Environment: Contamination is the number one cause of premature seal failure. Clean the exterior of the cylinder thoroughly and perform the disassembly and assembly in a clean, well-lit area.
Careful Disassembly:Mark the gland, piston, and tube for easy reassembly in the same orientation.
Inspect all metal components (cylinder rod, tube interior, piston, and gland) for scores, scratches, or pitting. Light polishing can address minor imperfections; severe damage requires component repair or replacement.
Proper Seal Installation:Lubricate Generously: Soak all new seals in clean hydraulic oil before installation. Lubricate all sealing surfaces and grooves.
Use the Right Tools: Always use seal picks, cone tools, or soft-tipped tools. Never use sharp screwdrivers or pliers that can nick or cut the seals.
Observe Direction: Pay close attention to the lip direction of piston and rod seals. Incorrect installation will cause immediate leakage.
Reassembly & Torque:Replace every seal from the old cylinder with the corresponding new part from the COGENG kit.
When reassembling, tighten the gland nut and other fasteners to the manufacturer's specified torque values using a torque wrench. Do not overtighten.
Final Checks:After reassembly and reinstallation, slowly cycle the boom cylinders several times without load to prime the system and seat the seals.
Check for leaks under low pressure first, then gradually increase to operating pressure. Monitor the cylinders closely during the first few hours of operation.
Frequently Asked QuestionsA. When will get the items after I place order?
Q. Once your payment is confirmed,we will arrange the goods within 1~4 days; if not in stock, we will inform you before placing the order?
A. If I only know the excavator model, but can not offer parts No.,what should I do ?
Q. If possible, you can send us pictures of old products, nameplate or the size for reference.
A. How can you guarantee the quality??
Q. We will 100% test the goods before delivery. We also support video inspection.
A. How long will it take to delivery to my address??
Q. The normal delivery time is 3-7 days, depending on which country you are in.?
A : Which delivery method will you choose?
Q : By sea, air or express(DHL,Fedex,TNT, UPS, EMS etc.)，Sometimes we will arrange as the customer's demand.
A: What's package? Can you give me the package according my requirement??
Q. We usually packed by standard exported box or carton. And yes we can pack as per your requirement.
A: Can the price be cheaper?
Q: Of course, you will be offered a good discount for a big amount.
A: Why should I choose to buy from you?
Q:Our advantages: 100% quality assurance, develop and manufature follow original ones;Quick response within 24 hours; Small order allowed;Reasonable stock and timely delivery;Neutral packing, customized packing are allowed. Positive customer feedback from abroad market;Excellent after-sales service.
A : Which payment terms can you accept?
Q : Paypal. Western Union, Bank Transfer, T/T...
