05802505 Bomag Hydraulic Motor A4FM28 for BW161 BW164

Product Overview

The 05802505 is a bent-axis axial piston fixed displacement motor used in the vibratory systems of Bomag BW 161 and BW 164 series road rollers, corresponding to the A4FM28 model (Bosch Rexroth bent-axis fixed displacement motor platform). The motor features a bent-axis design with a fixed displacement of 28 cm³/rev, installed in the vibratory drive circuit of Bomag tandem vibratory rollers to drive the vibration shaft and generate high-frequency centrifugal force for asphalt and soil compaction.

The A4FM28 employs Bosch Rexroth’s classic bent-axis axial piston technology, with pistons arranged at an angle to the drive shaft, transmitting torque through spherical contact between conical pistons and the drive plate. This design delivers excellent mechanical efficiency during low-speed starting and heavy-load conditions, with a compact structure suitable for the stringent installation space requirements of roller vibratory systems. The 05802505 is the Bomag parts system number corresponding to the A4FM28 model.

Engineered as a form-fit-function replacement for original Bomag 05802505 motors, this model maintains identical mounting flange dimensions, shaft specifications, and port locations, enabling drop-in interchangeability without modification to the host machine’s mounting interface or hydraulic circuit. Each unit undergoes 100% simulated load testing prior to shipment, validating output torque and volumetric efficiency against original specifications.

Technical Specifications 

• Model: 05802505

• Corresponding Model: A4FM28

• Original Brand: Bomag / Bosch Rexroth

• Motor Type: Bent-axis axial piston fixed displacement motor

• Design Feature: Bent-axis configuration, conical piston rotary group, fixed displacement

• Displacement: 28 cm³/rev

• Compatible Machines: Bomag BW 161, BW 164 series tandem vibratory rollers

• Application Position: Vibratory drive system

• Weight (approx.): 12.1 kg (reference A4FM28 standard configuration)

• Rotation: Bi-directional

• Mounting: Flange mounting (standard SAE or DIN configuration)

• Circuit: Open circuit / Closed circuit

• Seal Material: FKM (standard configuration)

Data Limitation Note: Detailed parameters such as rated pressure, peak pressure, and maximum speed for the A4FM28 were not found in publicly available search results. As a standard Bosch Rexroth model, the A4FM28 typically has a nominal pressure of 315–400 bar and a maximum speed of approximately 3,000–4,000 rpm. It is recommended to obtain the complete technical manual from Bosch Rexroth or an authorized Bomag dealer for final confirmation.

Key Technical Advantages

1. Bent-Axis Conical Piston Design with High Starting Efficiency

The A4FM28 employs Bosch Rexroth’s proven bent-axis design, with pistons arranged at an angle to the drive shaft, transmitting torque through spherical contact between conical pistons and the drive plate. This design delivers high mechanical efficiency during low-speed starting, with no significant difference between starting torque and running torque, suitable for the high-frequency reciprocating conditions required by roller vibratory drives. The self-centering characteristic of the conical piston rotary group reduces uneven wear risk, extending the service life of critical moving interfaces.

2. Compact Structure Optimized for Vibratory System Integration

The A4FM28 achieves a compact structural envelope at 28 cm³/rev displacement, weighing approximately 12.1 kg, suitable for installation in the vibratory drive circuit of Bomag BW 161/BW 164 rollers. The bent-axis configuration provides a compact axial dimension, facilitating piping layout and maintenance access within the limited space of the roller frame.

3. Form-Fit-Function Interchangeability with Zero Retrofit

The 05802505 maintains identical mounting flange dimensions, shaft specifications, and port locations to original Bomag parts, enabling direct replacement without modifying the host machine’s mounting interface or hydraulic circuit. The A4FM28 follows Bosch Rexroth standards for motor mounting dimensions and shaft interfaces, ensuring precise fit between the replacement and the host machine.

4. 100% Load Testing with Quality Assurance

Every 05802505 undergoes 100% simulated load testing on a dynamometer bench prior to shipment, validating volumetric efficiency and output torque. The product features FKM fluorocarbon seals suitable for the elevated temperatures of roller vibratory systems.

Application Areas

• Bomag BW 161 Series Tandem Rollers: Vibratory drive motors

• Bomag BW 164 Series Tandem Rollers: Vibratory drive motors

• Other Bomag BW 160 Series: Compatible vibratory system applications

Expert Maintenance Tips

1. Shaft Alignment Requirements: The bent-axis motor’s conical piston rotary group is sensitive to radial forces. During installation, ensure the coaxiality deviation between the motor shaft and drive-end spline does not exceed 0.05 mm. Excessive radial forces will accelerate wear on the piston tapered surfaces and drive plate.

2. Hydraulic Fluid Cleanliness Control: Maintain hydraulic fluid cleanliness at ISO 20/18/13 or better. Replace hydraulic fluid and filter elements every 1,000 operating hours or annually, with filter element filtration accuracy no less than 10 μm.

3. Vibratory Duty Special Notes: The 05802505 experiences high-frequency alternating loads in road roller vibratory drives. Inspect motor mounting bolt tightness and case drain leakage every 500 operating hours.

4. Initial Startup and Extended Storage: Fill the motor housing with clean hydraulic fluid during initial installation to prevent dry friction on piston pairs during startup. For motors stored over 6 months, manually rotate the shaft 2–3 revolutions to confirm free rotation, then run at low pressure under no load for 10 minutes before gradually applying load.