GM21VA Set Plate & Spherical Bush

The GM21VA Set Plate and Spherical Bush are key internal components of the hydraulic travel motor in excavators. They are part of the Nabtesco GM series hydraulic motors and play a critical role in ensuring proper alignment and smooth operation of the rotary group.

Set Plate

The set plate (also called the retainer plate in some manuals) functions to:

• Hold pistons and piston shoes in position

• Maintain correct spacing and alignment between piston assemblies

• Ensure smooth contact between moving parts, reducing wear

If the set plate is damaged or worn, pistons may misalign, causing internal leakage, vibration, or reduced motor efficiency.

Spherical Bush

The spherical bush (spherical bearing) allows:

• Rotational and slight angular movement of pistons or drive components

• Absorption of misalignment and axial load

• Reduction of friction and wear in high-pressure areas

It effectively connects moving parts while allowing small tilts, ensuring smooth operation of the hydraulic motor under load.

Why They Are Important

Together, the set plate and spherical bush:

• Ensure correct piston movement

• Maintain hydraulic efficiency

• Prevent internal damage to the rotary group

• Extend the life of the travel motor