Bafang BBS02 Installation Guide

1. Step 1 of 6

   Strip Crankset and Bottom Bracket

   Remove the pedals and use a crank puller to extract both the left and right crank arms. Use the splined bottom bracket tool to unthread the bottom bracket cups (remember: the drive-side bottom bracket is reverse-threaded on BSA standard frames, meaning you turn clockwise to loosen). Clean the empty bottom bracket shell thoroughly, removing all grease, dirt, and burrs.

   Schematic FIG. 1DIYPEV Technical Lab

   Removing the drive-side bottom bracket cup using a splined bottom bracket toolReference Blueprint Schematic

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2. Step 2 of 6

   Slide in the BBS02 Motor Spindle

   Slide the main axle spindle of the Bafang motor through the bottom bracket shell from the drive side (right) to the non-drive side (left). If the fit is tight, do not force it with a hammer; ensure the inside of the shell is clear of welds or internal cable routing guides. Push the motor until the gear housing bracket rests flush against the drive-side bottom bracket shell face.

   Schematic FIG. 2DIYPEV Technical Lab

   Inserting the Bafang BBS02 motor spindle through the clean bottom bracket shellReference Blueprint Schematic

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3. Step 3 of 6

   Attach the Mounting Bracket & Locknuts

   On the non-drive side, place the steel triangular mounting plate over the spindle. Insert the M6 mounting bolts through the plate into the motor body, but do not tighten them fully. Thread the large inner locknut onto the spindle and tighten it securely (30-40 Nm) using the Bafang lockring tool. This clamps the motor to the frame. Now tighten the M6 plate bolts. Finally, thread and tighten the outer locknut (cap nut) to lock the inner nut in place.

   Schematic FIG. 3DIYPEV Technical Lab

   Tightening the inner Bafang locknut using the specialized lockring toolReference Blueprint Schematic

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4. Step 4 of 6

   Mount the Chainring and Crank Arms

   Fit the Bafang chainring onto the motor housing and secure it with the five chainring bolts using a 5mm Allen key. Attach both Bafang crank arms to the square taper spindle, ensuring they are oriented at 180 degrees to each other. Secure the crank bolts tightly using an 8mm Allen key. Reinstall your pedals onto the new cranks.

   Schematic FIG. 4DIYPEV Technical Lab

   Mounting the Bafang chainring and crank arms onto the drive assemblyReference Blueprint Schematic

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5. Step 5 of 6

   Install Handlebar Controls and Route Wiring

   Mount the display, thumb throttle, and the e-brake levers (or brake sensors) onto your handlebars. Connect the primary 4-to-1 wiring harness to these components. Route the long harness down the frame tubes towards the motor. Mount the speed sensor on the rear chainstay and align the spoke magnet so it passes within 2-5mm of the sensor. Connect all color-coded waterproof plugs to the motor housing.

   Schematic FIG. 5DIYPEV Technical Lab

   Connecting the color-coded waterproof connectors at the handlebarsReference Blueprint Schematic

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6. Step 6 of 6

   Install the Battery Pack and Connect Power

   Secure the battery mounting cradle to the water bottle bosses on the down tube. If the frame lacks bottle cage bosses, use heavy-duty hose clamps or Rivnuts to secure the cradle. Connect the positive and negative power leads from the motor controller to the battery cradle terminals using XT60/XT90 connectors. Slide the battery pack into its cradle, lock it with the key, and power on the system to test.

   Schematic FIG. 6DIYPEV Technical Lab

   Mounting the lithium-ion battery cradle to the bicycle frame down tubeReference Blueprint Schematic

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Managing Chainline and Frame Clearance

One of the most critical aspects of a successful BBS02 conversion is achieving proper frame clearance and chainline. The motor's gear reducer housing requires space next to the right-side chainstay. On some frames with flared chainstays, the motor housing may press against the frame before the axle is fully seated. If this occurs, you must place 1mm or 2mm bottom bracket spacers on the drive-side spindle before inserting the motor.

However, adding spacers pushes the drive unit further to the right, which worsens the chainline. A poor chainline can lead to premature wear of the chain, chain drops, or noisy operation. Using high-quality chains designed for e-bikes, along with a dished chainring, is highly recommended to mitigate these issues and ensure smooth shifting across the cassette.

Electrical Wire Routing and Drip Loops

Proper wire management is essential to prevent water ingress and cable damage. Run the primary harness along the underside of the down tube, securing it with nylon zip ties or adhesive cable guides. Ensure there is enough slack around the handlebar area to allow full steering rotation without straining the plugs. At the bottom bracket, form a small "drip loop" in the wires so that any rainwater running down the cables drips off onto the ground before reaching the waterproof connectors.