E-Bike Motor Greasing and Noise Reduction

1. Step 1 of 6

   Remove the Motor from the Frame

   Unplug all electrical connections. Remove the crank arms, pedals, chainring, and non-drive side lockrings. Slide the motor unit out of the bottom bracket shell. Place the motor on a clean, stable workbench with the drive side facing up.

   Schematic FIG. 1DIYPEV Technical Lab

   Detached Bafang mid-drive motor resting on a clean workbenchReference Blueprint Schematic

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2. Step 2 of 6

   Open the Secondary Gear Cover Plate

   Use a 4mm Allen key to remove the five screws securing the black steel cover plate on the drive side. Insert a thin flathead screwdriver into the notch on the side of the cover and gently pry it upward. Be careful not to tear the thin paper gasket underneath. Lift off the plate to expose the large steel gear.

   Schematic FIG. 2DIYPEV Technical Lab

   Prying open the black steel gear cover plate on the Bafang motor casingReference Blueprint Schematic

   Alt description tag verifiedScale: NTS (Not To Scale)
3. Step 3 of 6

   Extract and Clean the Steel Pinion Gear

   Pull the large steel gear spindle assembly straight up out of the housing (this may require some effort as the axle fits tightly in its support bearing). Wipe away the old, blackened grease from the steel gear teeth, the pinion gear cavity, and the internal housing walls using lint-free rags. Spray degreaser to remove all residual grit, then dry completely.

   Schematic FIG. 3DIYPEV Technical Lab

   Lifting the large steel gear assembly out of the Bafang motor casingReference Blueprint Schematic

   Alt description tag verifiedScale: NTS (Not To Scale)
4. Step 4 of 6

   Inspect the Gears for Damage

   Examine the teeth on the steel gear and the internal helical nylon gear (visible through the spindle shaft port). Look for chipped, worn, or stripped teeth. If the nylon gear has melted teeth or flat spots due to motor overheating, you must dismantle the motor core from the opposite side and replace the nylon gear.

   Schematic FIG. 4DIYPEV Technical Lab

   Inspecting the internal white nylon gear teeth inside the Bafang caseReference Blueprint Schematic

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5. Step 5 of 6

   Apply Plastic-Safe Grease

   Using a clean brush or rubber glove, apply a generous layer of Mobil 28 grease to the steel gear teeth and pack the internal cavity. Slide the steel gear shaft back into the housing, rotating it slightly to align the teeth. Apply grease to the needle bearings and the main spindle shaft. Do not overfill the casing; there should be space for grease movement.

   Schematic FIG. 5DIYPEV Technical Lab

   Applying red Mobil 28 grease onto the teeth of the gear assemblyReference Blueprint Schematic

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6. Step 6 of 6

   Seal and Reassemble the Motor

   Ensure the paper gasket is aligned correctly on the casing interface. Place the steel cover plate back on the casing. Thread the five M5 cover screws and tighten them in a star pattern to 5 Nm of torque. Re-mount the motor unit onto the bicycle frame, connect all cables, and run the motor on a stand to verify quiet, smooth operation.

   Schematic FIG. 6DIYPEV Technical Lab

   Tightening the cover screws in an alternating pattern with a hex keyReference Blueprint Schematic

   Alt description tag verifiedScale: NTS (Not To Scale)

The Dual-Stage Gear Reduction System

Bafang mid-drives utilize a dual-stage gear reduction system to convert the high-RPM spin of the electric motor stator into a usable pedaling cadence (typically 80-120 RPM). The first stage is a helical nylon gear driven by the motor's steel pinion shaft. Helical gears have curved teeth that engage gradually, which is why Bafang motors run so quietly compared to straight-cut gearboxes. The second stage is a steel-on-steel pinion gear driving the main bottom bracket axle, which multiplies torque to propel the bicycle.

Because these two stages operate under different loads and materials, they require separate lubrication maintenance. The primary nylon gear is lubricated from the motor-stator side of the housing, while the secondary steel gears are accessed through the outer cover plate. Use the comparison table below to identify correct greases for each compartment.

Avoiding Over-Greasing Pitfalls

While dry gears cause friction noise and premature wear, over-packing the gear housing can lead to severe electronic damage. When the motor gets hot, excess grease expands and is pushed past the internal rubber shaft seals. It can travel down the wire channels directly into the controller compartment. If the grease contacts the controller board, it can trap heat, dissolve conformal coatings, and cause electrical short circuits on the control lines.