Bosch e-bike motor: identify the generation and find the right spare parts
Anyone looking for spare parts for a Bosch drive rarely struggles with availability, but rather with identification. Crankshaft bearings, freewheels, seals and lockring tools differ from generation to generation. What matters is the type designation on the motor, not its appearance.
Step 1: Read the BDU designation
The housing of the drive unit carries a type designation beginning with “BDU”. This is how to classify it (based on the Bosch operating manuals for the respective drive units):
- BDU2xx = 2nd generation: BDU250C and BDU255C (Active Line), BDU250P (Performance Line Cruise), BDU290P (Performance Line Speed) and BDU250P CX (Performance Line CX).
- BDU310, BDU350, BDU365 = 3rd generation: Active Line, Active Line Plus and Performance Line.
- BDU450 CX and BDU490P = 4th generation in the Bosch eBike System 2: Performance Line CX and Performance Line Speed.
- Four-digit designations such as BDU3740 or BDU3741 belong to the Bosch Smart System (Performance Line CX). Here, compare the exact designation with the compatibility information of the spare part.
Step 2: Compare the lockring
On the 2nd generation, a lockring with an outer diameter of around 50 mm holds the chainring. From the 3rd generation onwards, the ring is smaller (around 40 to 45 mm). That is why Gen2 needs a different lockring tool from the later generations: Spider for Gen2 (€24.95), for Gen3 (€29.95), for Gen4 (€29.95); prices at bikely as of 10 October 2026.
Step 3: Use the year of manufacture only as a guide
The 2nd generation was fitted from model year 2014. The Active Line of the 3rd generation arrived for model year 2018, the Performance Line CX of the 4th generation for model year 2020. Because the series were produced for different lengths of time, the year of manufacture is only a rough indication. The BDU designation is what counts.
Why identification matters
Bearings, freewheels and seals have their own part numbers for each generation. A part only fits if your generation is listed in its compatibility information.
Matching parts by generation: Bosch Gen2 · Bosch Gen3 · Bosch Gen4 · Assembly tools for the lockring
Sources: Bosch manual Active Line/Performance Line (BDU2xx) · Bosch manual BDU3xx · Bosch manual BDU4xx · Bosch manual BDU374x · Park Tool: lockring tools · electrive on the Active Line 2018 · emtb-news on the Performance Line CX 2020. As of: October 2026.
