SHIBATA GRK-R / GRK5-R Idler Spacer Set – 1mm Aluminum / 1.9mm POM

The SHIBATA GRK Idler Spacer Sets are genuine replacement and tuning components for the GRK-R and GRK5-R drivetrain gear assemblies.

Choose between the original 1mm replacement spacer or the newer 1.9mm POM low-friction spacer, depending on your chassis setup and drivetrain configuration.

R31S123 – 1mm Standard Idler Spacer
This is the standard 1mm-thick idler spacer used in the GRK-R and GRK5-R gear components. It is ideal as a direct replacement or spare part and can also be used as a replacement component for the R31S024 integrated axle shaft. Two spacers are included.

R31S139 – 1.9mm POM Low-Friction Idler Spacer
This upgraded spacer is manufactured from POM resin and was adopted for the GRK5-R HRP Full Kit. The POM material is intended to reduce friction caused by rotational contact within the drivetrain. It is compatible with GRK5-R kits and GRKRCV-converted vehicles. 

Important Installation Note

The 1.9mm R31S139 POM spacers are not a direct one-for-one replacement for only the 1mm spacer.

SHIBATA specifies that when converting to R31S139, the existing 3mm and 1mm aluminum idler spacers are both replaced with 1.9mm POM spacers. Because this changes the front-to-rear position of the idler gear, the idler shaft orientation or gear position may need adjustment depending on whether the chassis uses a front- or rear-motor configuration.

Key Features

• Genuine SHIBATA / GRK drivetrain components
• Designed for GRK-R and GRK5-R gear assemblies
• Two spacer options in one listing
• R31S123: 1mm standard replacement spacer
• R31S139: 1.9mm POM low-friction upgrade
• R31S139 helps reduce rotational friction
• R31S123 also fits the R31S024 integrated axle shaft
• Two spacers included per package
• Ideal for replacement, repair, or drivetrain tuning

Compatibility

R31S123

• GRK-R
• GRK5-R
• R31S024 Integrated Axle Shaft applications 

R31S139

• GRK5-R
• GRKRCV converted vehicles
• GRK5-R HRP drivetrain configuration