Main Gear Upgrade for XRB-SR 4mm Mast HRB-0301043 by HIROBO  [HRB-0301043]

How the XRB-SR Main Gear Performs

This RC-scale main gear replaces the original on XRB-SR series helicopters that use a 4mm main mast. It functions as a direct drivetrain spare to assist with maintenance, setup checks, and tuning adjustments on electric RC helicopters.

When fitting, make sure the gear sits square on the 4mm mast, check axial alignment with the pinion and spur gear mesh, and ensure the main shaft turns freely before conducting test flights. Attention to mesh and seating lowers vibration and helps keep consistent rotor tracking.

Use the gear to re-establish correct engagement after wear, then re-verify head geometry and blade tracking as part of your tuning routine. This product is an aftermarket accessory for model helicopter drivetrain work.

Keep this part on hand as a like-for-like spare for scheduled gearbox servicing or when wear is detected; always confirm fit with your XRB-SR configuration and perform mesh and tracking checks after installation.