0365401 Original Excavator Swing Motor Hydraulic Sub Piston for EX270 EX370-5 ZX870-3

Part number 0365401 is a specialized part number for Hitachi's original rotary motor plunger (hydraulic auxiliary piston). This component is the core moving part of the rotary motor (rotary motor) plunger pump, responsible for reciprocating motion in the high-speed rotating cylinder body, converting hydraulic energy into mechanical torque. According to publicly available accessory adaptation information, it is mainly suitable for the rotary motor of large hydraulic excavators such as Hitachi EX1200-6. In the aftermarket, this component is often directly referred to as a "rotary motor plunger" or "hydraulic piston".

The hydraulic secondary piston (plunger) is the core working element inside the inclined disc axial piston motor/pump. Its core function is to perform precise reciprocating linear motion in the plunger hole of the cylinder body under the drive of high-pressure oil, and through the sliding cooperation with the inclined plate, convert the pressure energy of the oil into mechanical energy for the rotation of the drive shaft, thereby outputting a huge rotational torque. Its head is usually embedded with wear-resistant copper alloy or engineering plastic sliding shoes to reduce friction and wear with the inclined plate. Precise dimensional tolerances and excellent wear resistance ensure dynamic sealing between the plunger and cylinder bore, resulting in minimal leakage under high pressure. This is the key to ensuring the efficiency, torque, and response speed of the rotary motor.

The maintenance core of this plunger lies in monitoring the quality of hydraulic oil and conducting regular professional inspections. Daily prevention: It is necessary to strictly follow the maintenance cycle (usually every 1000 working hours) to replace the hydraulic oil and return oil filter element, and regularly conduct oil contamination testing, because small solid particles are the main cause of plunger and cylinder bore strain and wear. Fault symptoms: If the excavator experiences weak rotation, slow rotation speed, excessive slip (inaccurate positioning) when rotation stops, or abnormal noise from the rotation motor, it may indicate that the plunger cylinder pair has worn out. When installing a new plunger, it is necessary to ensure that the cylinder bore is clean and undamaged, and apply clean hydraulic oil to the surface of the plunger and slide shoe. After maintenance, the rotary system needs to undergo exhaust and pressure testing to ensure performance recovery.