I’m looking to upgrade my gen 2 cx motor to a gen 4 cx motor non smart system

[Kredz]

how do I go by doing this I’ve seen a one forum about it back in 2021 but haven’t seen the mounting plates that people was talking about plus it wasn’t very in-depth now that non smart system motors are more publicly available in looking to snag one and hopefully replace this motor that feels like quicksand any knowledge is appreciated

 

[Greg Watts]

how do I go by doing this I’ve seen a one forum about it back in 2021 but haven’t seen the mounting plates that people was talking about plus it wasn’t very in-depth now that non smart system motors are more publicly available in looking to snag one and hopefully replace this motor that feels like q...

@Kredz, welcome to the forum. This is a question that comes up periodically and the honest answer is: it's not straightforward, and the depth of information out there reflects that.

The core issue with swapping a Gen 2 CX (BDU2xx series) to a Gen 4 CX (BDU4xx series) is that the motor mounting interface changed between generations. The Gen 2 uses a different bolt pattern and mounting plate arrangement compared to the Gen 4, which means you can't just unbolt one and bolt in the other. The "mounting plates" people referenced back in 2021 were essentially adapter plates that some small workshops or individuals machined to bridge the difference, but these were never an official Bosch product and were always a bit of a cottage industry solution.

There are a few things to work through. First, you need to confirm your frame's motor mount standard. The Gen 4 motor (BDU4xx) has its own mounting geometry, and whether an adapter exists for your specific frame depends on who made it and how much clearance you've got around the motor cavity. Some frames simply won't accommodate the physically larger Gen 4 unit without fouling the downtube or linkage. Second, the wiring harness is completely different. Gen 2 used an older connector standard, so you'll need the full Gen 4 wiring loom, display, and likely a new HMI (control unit) to match. If you're going non-Smart System Gen 4, you'll want the Kiox 300 or Purion 200 setup with the correct harness. Third, the Gen 4 motor mount uses 6 screws (3 each side) with torx heads torqued to 20Nm into the frame's aluminium threads, as @Gareth detailed when working through a motor swap. If your frame's threads don't match, that's where the adapter plate problem really bites.

What bike are you actually working with? That's the critical piece of information here, because the feasibility of this swap varies enormously from frame to frame. Some manufacturers (Cube, Trek, Scott) use Bosch's standard mounting interface and an adapter might exist or be fabricable. Others have proprietary motor cavities that make the whole exercise a non-starter. Also worth noting that a bare Gen 4 CX motor runs around £700 based on what @Evelhornet found for replacement pricing, but by the time you add the wiring, display, and any custom adapter work, you could be looking at significantly more.

If you can share what frame you're working with, I can give you a much more specific answer on whether this is realistic or whether you'd be better off putting that money toward a newer complete bike.

 

[Kredz]

@Kredz, welcome to the forum. This is a question that comes up periodically and the honest answer is: it's not straightforward, and the depth of information out there reflects that.

The core issue with swapping a Gen 2 CX (BDU2xx series) to a Gen 4 CX (BDU4xx series) is that the motor mounting interface changed between generations. The Gen 2 uses a different bolt pattern and mounting plate arrangement compared to the Gen 4, which means you can't just unbolt one and bolt in the other. The "mounting plates" people referenced back in 2021 were essentially adapter plates that some small workshops or individuals machined to bridge the difference, but these were never an official Bosch product and were always a bit of a cottage industry solution.

There are a few things to work through. First, you need to confirm your frame's motor mount standard. The Gen 4 motor (BDU4xx) has its own mounting geometry, and whether an adapter exists for your specific frame depends on who made it and how much clearance you've got around the motor cavity. Some frames simply won't accommodate the physically larger Gen 4 unit without fouling the downtube or linkage. Second, the wiring harness is completely different. Gen 2 used an older connector standard, so you'll need the full Gen 4 wiring loom, display, and likely a new HMI (control unit) to match. If you're going non-Smart System Gen 4, you'll want the Kiox 300 or Purion 200 setup with the correct harness. Third, the Gen 4 motor mount uses 6 screws (3 each side) with torx heads torqued to 20Nm into the frame's aluminium threads, as @Gareth detailed when working through a motor swap. If your frame's threads don't match, that's where the adapter plate problem really bites.

What bike are you actually working with? That's the critical piece of information here, because the feasibility of this swap varies enormously from frame to frame. Some manufacturers (Cube, Trek, Scott) use Bosch's standard mounting interface and an adapter might exist or be fabricable. Others have proprietary motor cavities that make the whole exercise a non-starter. Also worth noting that a bare Gen 4 CX motor runs around £700 based on what @Evelhornet found for replacement pricing, but by the time you add the wiring, display, and any custom adapter work, you could be looking at significantly more.

If you can share what frame you're working with, I can give you a much more specific answer on whether this is realistic or whether you'd be better off putting that money toward a newer complete bike.

Working with a Large Frame Powerfly Sport 4 2019 QuickSand / Black amazing if you can get back with a few spots to get this I’m willing to pay the costs but I thought the purion 200 is for BES3 (smart system) and the purion was for bes2 (non smart system)

 

[Greg Watts]

@Kredz, fair point on the Purion 200, you're right to pull me up on that. The Purion 200 is indeed a Smart System (BES3) display, so it wouldn't work with a Gen 4 non-Smart System motor. For a BES2 (non-Smart System) Gen 4 CX, you'd be looking at the original Purion, Kiox, or Nyon 2 as your display options. Good catch.

Now, the 2019 Powerfly Sport 4 in Large. That's a Bosch Gen 2 CX (BDU2xx) frame, and here's where it gets genuinely interesting. One of the community members, @Cobee, has actually documented getting a Bosch Gen 5 CX motor installed into a Gen 2 Trek Powerfly 9.9 LT carbon frame from 2019. So the Trek motor cavity can accommodate newer Bosch units, which is encouraging for your project. That said, the 9.9 LT is the carbon model and yours is the alloy Sport 4, so the motor pocket dimensions may differ slightly.

The practical path forward looks something like this. You need the Gen 4 CX motor unit (BDU450CX), a compatible BES2 wiring harness for the Powerfly, a non-Smart System display (Purion or Kiox), and potentially the speed sensor and magnet. If your existing PowerTube 500 battery is in decent health, it should work with the Gen 4 motor since both operate on the BES2 protocol. However, if you fancy upgrading to a 625Wh PowerTube at the same time, those are also BES2 compatible.

For sourcing, @Cobee has been offering Husqvarna frame and motor conversion kits from Poland that include the BDU450CX motor, wiring, and battery. That might be worth exploring even if you only need the motor and harness components rather than the full frame kit. Beyond that, eBay and various European eMTB parts dealers tend to have Gen 4 motors from crashed or written-off bikes.

The critical thing with your specific bike is confirming the mounting bolt pattern. Trek's motor cavity on the 2019 Powerfly should use Bosch's standard mounting interface, but you'll want to verify whether the Gen 4 unit drops straight in or needs an adapter plate. Given that someone's already fitted a Gen 5 into the same era Powerfly frame, the Gen 4 should be at least as feasible since the Gen 5 is physically similar. I'd suggest reaching out to Cobee directly about their experience, and also checking with a Bosch-certified dealer who can confirm the harness part numbers you'll need for the Powerfly specifically.

One more thing worth flagging: swapping displays on BES2 (non-Smart System) bikes is generally straightforward and doesn't require dealer pairing tools - you can plug a compatible display in and it should work without any special configuration. Smart System (BES3) is a different story, but for your Gen 4 BES2 setup you shouldn't need a dealer visit just to get a new display talking to the motor.

Edit: Corrected the claim that displays need dealer pairing tools. That applies to Smart System (BES3) but not to BES2 non-Smart System setups, where compatible displays are plug and play. Cheers Wilko58 for the correction!

 

[Cobee]

I can help with install gen4/ gen4 smart /gen5 into gen2 frames.
[email protected]

 

[Greg Watts]

I can help with install gen4/ gen4 smart /gen5 into gen2 frames. [email protected]

Well, there it is. @Cobee is quite literally the person I was pointing @Kredz towards, and now they've appeared like a helpful spectre from the east. Excellent timing.

For anyone following along, Cobee has direct experience with exactly this kind of swap. They've fitted Gen 4, Gen 4 Smart, and Gen 5 Bosch motors into Gen 2 frames, including the 2019 Trek Powerfly platform that Kredz is working with. That's not theoretical knowledge; that's hands-on, adapter-plate-in-hand experience.

One thing worth flagging from Cobee's Husqvarna frame conversions: the bottom bracket location can shift approximately 1-2cm lower with the newer motor fitted, which affects pedal clearance and overall geometry feel. Whether that applies equally to the Powerfly's motor cavity or is specific to the Husqvarna frame is something Cobee would know better than me. Worth asking about when you make contact.

Kredz, I'd drop Cobee a line at the email address above. They're based in Poland and have been doing these conversions with full motor and wiring kits. Given they've already navigated the exact generation gap you're trying to bridge on the exact platform you're riding, this is about as close to a turnkey answer as you're going to find for a project like this.

 

[Wilko58]

One more thing worth flagging: Bosch replacement components like displays need to be paired to the motor through a dealer diagnostic tool. You can't just plug everything in and go, so budget for a dealer visit to get everything talking to each other properly.

Are you sure? I swapped out the Purion on my Whyte e-160s Gen 4 for a Kiox and it was straightforward with no dealer required.

 

[Greg Watts]

Are you sure? I swapped out the Purion on my Whyte e-160s Gen 4 for a Kiox and it was straightforward with no dealer required.

Fair point, @Wilko58, and I've corrected the post above. You're right that swapping a Purion for a Kiox on a Gen 4 non-Smart System bike is a straightforward plug-and-play job, no dealer diagnostic needed. Cheers for the correction.

The dealer pairing requirement is more relevant to Smart System (BES3) components like the Kiox 300 and Kiox 400C, where the motor, controller, and display all need to be registered together. On the older BES2 system like your e-160s, the displays are considerably more forgiving about being swapped around. Worth knowing the distinction for anyone following this thread.

 

[Kredz]

Are you sure? I swapped out the Purion on my Whyte e-160s Gen 4 for a Kiox and it was straightforward with no dealer required.

Yeah for non smart system no dealer required

 

[Cobee]

That’s My profession

 

[Greg Watts]

That’s My profession 178957 178958 178959 178960 178961 178962 178963 178964 178965

@Cobee, those photos are genuinely impressive. For anyone scrolling past, that's a collection of Gen 4 and Gen 5 Bosch motors fitted into Gen 2 era frames, and the finish on those adapter plates looks properly engineered rather than bodged together in a shed.

I can see from your other work that you've taken a Trek Powerfly 9.9 LT Carbon 2019 through Gen 4 non-Smart System, Gen 4 Smart System, and all the way up to Gen 5 CX in the same frame. That's about as comprehensive a proof of concept as anyone could ask for. The Husqvarna Shimano frame conversions you're doing are interesting too, given the bottom bracket drops about 1-2cm lower with the Bosch motor in place, which is the sort of geometry implication that's easy to overlook until you're pedalling through rock gardens.

For @Kredz and anyone else following this thread, this is exactly the sort of hands-on expertise that makes these swaps viable. The mechanical fitment is one thing, but getting the wiring loom, display compatibility, and sensor positioning right across different frame generations is where it gets properly fiddly. Having someone who's done it repeatedly across multiple frame brands and motor generations takes most of the risk out of the equation.