CAT 399-8586 BEARING-SLV-GD

The CAT 399-8586 (3998586) YM is a stick hydraulic cylinder assembly for Caterpillar medium-duty excavators. It is primarily compatible with the stick drive of mainstream excavators such as the CAT 320D2/323D2/326D2, controlling the stick’s extension and retraction movements and efficiently converting hydraulic energy into mechanical energy. Suitable for heavy-duty excavation conditions, the YM version is a high-quality replacement with performance close to the original parts, offering better value for money. The following is the core information:

Core Technical Parameters

Item Details
Part Model: CAT 399-8586 (3998586) YM boom hydraulic cylinder assembly, double-acting single-rod piston type, with buffer + dustproof structure

Core Materials: Cylinder barrel: 27SiMn seamless alloy steel pipe, inner wall rolled + quenched (Ra≤0.4 μm, HRC 50–55); Piston rod: 40Cr, hard chrome plated (plating thickness 0.05–0.08 mm, HRC 60–65); End cap / Earring: 42CrMo forged steel, overall heat treated

Key Dimensions: Cylinder diameter 120 mm, rod diameter 70 mm, stroke 1650 mm, total length 2500 mm, earring bore diameter 50 mm, working pressure 35 MPa (350 bar), burst pressure 87.5 MPa, single weight approx. 85 kg

Compatible Models: CAT 320D2/320GC/323D2/326D2/330D2 excavators, adapted for stick drive circuit, compatible with original factory hydraulic system.

Core Configuration: Built-in two-way buffer valve, imported NOK seals (Glydring + Sterling ring combination), dust seal, wear-resistant support ring, with oil port connector (PT 3/4″) and lug pin hole.

Core Functions and Structural Features:

Heavy-duty drive and high efficiency: Adapts to 35 MPa system pressure, providing approximately 339 kN thrust and 184 kN pull force, meeting the heavy-duty excavation needs of rock and clay. Two-way buffer design reduces stick retraction and extension impact, protecting structural components and the hydraulic system.

Wear-resistant and corrosion-resistant: Cylinder barrel roll hardening + The piston rod features a hard chrome plating, providing wear and corrosion resistance, making it suitable for harsh working conditions such as construction site dust and mud. The seals are made of oil-resistant polyurethane, ensuring leak-proof performance and a long service life.

Stable and Fault-Proof: An internal buffer valve prevents high-pressure impacts, and a dust seal blocks external impurities, reducing seal wear and hydraulic oil contamination, thus lowering the probability of cylinder leaks and jamming.

Easy Installation: The lugs have locating pin holes, and the oil port markings are clear, fitting the original mounting position for direct replacement without modifying pipelines or brackets, shortening replacement time.

Installation and Maintenance Points:
Installation Specifications: Clean the cylinder flange face, lugs, and pins, removing burrs and oil stains. Check the seals for damage. Use specialized tooling for installation to avoid scratching the piston rod surface.

Tighten the lug bolts diagonally, controlling the torque to 280–320 N·m. For the oil port joints, use thread sealant + torque 55–65 N·m for tightening to prevent leakage.

After assembly, run the cylinder unloaded for 5–10 cycles. Next, purge all air, check for leaks and blockages, and ensure the buffering effect is normal before putting it into heavy-duty operation.

Maintenance Recommendations:
Every 200 working hours, check for scratches on the piston rod, leaks at the seals, and looseness of the lug bushings. Address any problems promptly.

Every 500 working hours, replace the hydraulic oil filter element. Use CAT DEO dedicated hydraulic oil (ISO VG 46), maintaining oil cleanliness within NAS 8 level.

Every 1500–2000 working hours, replace the seals to prevent aging and leakage. If the piston rod plating damage is >0.2 mm, repair or replace the entire assembly.