Polaris - Wheel Sprocket Assembly with Bearing for 3900 Sport (39-420) - W7640045

Polaris – Wheel Sprocket Assembly with Bearing for 3900 Sport (39-420)

This genuine Polaris replacement wheel sprocket assembly with integrated bearing (part reference 39-420) is a key drivetrain component for the Polaris 3900 Sport pressure-side automatic pool cleaner. It sits at position 10 in the official Fluidra exploded-view diagram and is essential for transferring power from the drive chain to the wheels, keeping your cleaner moving efficiently across the pool floor and walls.

How It Works

The Polaris 3900 Sport uses a PosiDrive system in which a stainless-steel drive chain wraps around the wheel sprockets, transmitting torque from the gearbox to the cleaner’s wheels. This sprocket assembly features toothed outer edges that engage the drive chain, while the integrated bearing at its centre allows smooth, low-friction rotation. Two of these sprocket assemblies are required per cleaner — one per driven wheel — and worn or seized bearings are a common cause of erratic movement or loss of drive.

Compatibility

This assembly is designed exclusively for the Polaris 3900 Sport pressure-side pool cleaner (model W7620000). It is not interchangeable with other Polaris pressure-side models such as the 380 or 360. Always verify your exact cleaner model before ordering to ensure a precise fit.

Why Genuine Matters

Sourced directly through Fluidra’s official parts programme, this OEM assembly is manufactured to the same specifications as the factory-fitted part, ensuring correct chain engagement and bearing longevity. Aftermarket sprockets can have slightly different tooth profiles or bearing tolerances, which may cause premature chain wear or inconsistent drive performance — risks avoided when fitting a genuine Polaris part.