Automatic Brick: BMW K100 CVT Cafe Racer

BMW K100 Cafe Racer

Retro Rides by Lourenço builds a CVT cafe racer for a disabled rider…

The BMW K100 “Flying Brick” has become an unexpected darling of the customs scene, a four-cylinder, fuel-injected, shaft-drive machine with the 987cc engine laid flat on its side in the frame, giving the bike its nickname. Produced from 1982-92, the “Flying Brick” is a favorite donor of our new friend Gustavo Lourenço, who runs Brazil’s Retrorides by Lourenço — a family-run workshop that’s been in business for more than 30 years, building award-winning cars and motorcycles. Says Gustavo:

“I have been passionate about motorcycles since I was a kid. When my father still ran the workshop, he always had different cars and motorcycles, so you could say my passion came from blood…”

BMW K100 Cafe Racer

Recently, a friend came into the shop with a new challenge for the team:

“He told us how he missed riding a motorcycle, because with his disability, he could ride only a scooter (he can’t move his left foot).  So he asked us if we could make that dream come true.”

BMW K100 Cafe Racer

Gustavo, who works with his father, José, and brother, Rodrigo, jumped at the chance to realize the customer’s dream. Their donor motorcycle, an ’84 K100RS, would have to be transformed from a traditional 5-speed sequential manual transmission into an automatic — easier said than done.

“After months of drawings and drafts, we decided that the best way to turn the bike into automatic would be to build a CVT transmission starting from scratch.”

BMW K100 Cafe Racer

And building a CVT (Continuously Variable Transmission) wasn’t the only challenge:

“In the K series motorcycles, the swingarm anchoring point is the gearbox, and when we removed it, we had nowhere else to anchor the swingarm — the solution was to create a cage to solve this problem.”

BMW K100 Cafe Racer

After four months of development, a ton of work in CAD, and enough math to drive Gustavo nearly crazy, they had a prototype ready to install, complete with an exclusive horizontal suspension system. Fortunately, the scratch-built transmission performed much better than anyone even hoped, especially in light of the weight savings they’d achieved with billet aluminum parts:

“The ratio between the CVT pulleys was perfect, which was where we were most afraid of making a mistake, as we did a lot of calculations to reach this result.”

BMW K100 Cafe Racer

But the very best part was still to come — the customer’s first ride:

“The bike was very easy to ride and he came back crying, and made everyone in the workshop cry too. It was really exciting and I will never forget that moment. It made us proud because we helped him and could make his dream come true.”

BMW K100 Cafe Racer

Kudos to Gustavo, José, Rodrigo, and the rest of the Retro Rides crew for making this incredible build a reality. Below, we get the full details from Gustavo himself, as well as more stunning shots from photographer Rodrigo Lizardi (@lizardirodrigo).

Gustavo and team have created an e-book called The Cafe Racer Bible to help anyone building their BMW K series on their own, complete with 3D plans!

BMW K100 Automatic: Builder Interview

BMW K100 Cafe Racer

• Please tell us a bit about yourself, your history with motorcycles, and your workshop.

My name is Gustavo Lourenço, and I live in Brazil. We have a workshop called Retrorides by Lourenço, where we work customizing cars and motorcycles, especially hot rods and cafe racers.

I have been passionate about motorcycles since I was a kid. When my father still ran the workshop, he always had different cars and motorcycles, so that passion came from blood…

BMW K100 Cafe Racer

Our workshop is in Campinas, SP, and we like really different projects. We specialize in manufacturing machined aluminum parts — design is also another passion in my life…

The workshop has been in existence for over 30 years and during all that time we have been manufacturing award-winning cars and motorcycles in the most notorious shows around the country.

We work as a family. My father, José, and my brother, Rodrigo — we believe that our projects are authentic due to the passion we have for our work.

BMW K100 Cafe Racer

• What’s the make, model, and year of the bike?

BMW K100RS, 1984.

BMW K100 Cafe Racer

• Why was this bike built?

We always have some bikes to use as a base here in the workshop to offer to our customers. One day a friend came in and he told us how he missed riding a motorcycle, because with his disability, he could ride only a scooter (he can’t move his left foot).

So he asked us if we could make that dream come true. We decided to meet this challenge and realize this customer’s dream.

BMW K100 Cafe Racer

After months of drawings and drafts, we decided that the best way to turn the bike into automatic would be to build a CVT transmission starting from scratch. It took four months for the first prototype to be installed on the bike and to be tested, we had to do so many mathematical calculations I almost went crazy.

We tested the bike and it was fantastic, with performance that surprised me. The bike was very easy to ride and when the customer rides for the first time the bike, he cried, and made everyone in the workshop cry too, it was really exciting and I will never forget that moment.

BMW K100 Cafe Racer

• What was the design concept and what influenced the build?

We always prioritize the bike’s lines, and we were very concerned that the bike wouldn’t turn ugly with the new transmission. Another thing that we prioritize a lot in our projects is weight savings / lightness, so we chose to build all the parts in billet machined aluminum.

BMW K100 Cafe Racer

• What custom work was done to the bike?

The motorcycle frame was cut and the parts were all designed in CAD software — we created an exclusive horizontal suspension system…

BMW K100 Cafe Racer

The most difficult task of this project was to design the transmission, because in the K series motorcycles, the swingarm anchoring point is the gearbox, and when we removed it, we had nowhere else to anchor the swingarm — the solution was to create a cage to solve this problem.

BMW K100 Cafe Racer

• Does the bike have a nickname?

No, just “Flying Brick.”

BMW K100 Cafe Racer

• Can you tell us what it’s like to ride this bike?

I was impressed how fast the bike got due to the weight savings. The ratio between the CVT pulleys was perfect, which was where we were most afraid of making a mistake, as we did a lot of calculations to reach this result.

The bike was very nice and very, very easy to ride — the bike became a real toy.

BMW K100 Cafe Racer

• Was there anything done during this build that you are particularly proud of?

Certainly what I liked the most was the customer’s first ride on the bike… He came back crying, and made everyone in the workshop cry too. It made us proud because we helped him and could make his dream come true.

BMW K100 Cafe Racer

More Detail Shots

See the K100 CTV in Action…

Follow the Builder

Gustavo and team have created an e-book called The Cafe Racer Bible to help anyone building their BMW K series on their own, complete with 3D plans!

7 Comments

  1. Great job guys. Do you have plans to build more automatics now that the hard part has been done? I applaud you on listening to your customer and delivering a product to such high standards. I would imagine you improved the brakes to compensate for the lack of engine braking but there is no reference to such a detail in such a short story.

    • Engine braking with a cvt is determined by the clutch engagement rpm – which btw was never talked about, I’m wondering if they used a Rekluse clutch or if the cvt has a centrifugal engagement clutch within it – and the driven pulley torque spring (higher rate will have a quicker downshift function giving more engine braking). There is nothing inherent to cvt’s that excludes engine braking, and it’s perfectly possible to have as much engine braking as one wants with a cvt. Again, this is largely a matter of tuning.

  2. O.k., concerning this bike:
    1. I’m not saying the CVT isn’t cool, but a very simply solution would’ve been to have a left throttle shift similar to Vespa and Lambretta scooters. Yes, it would have required the use of the left hand, but as the video states the ability to manually shift a motorcycle is one of its “most pleasureable features,” plus it would’ve been a solution that could’ve been designed and applied in perhaps a couple days, at most.
    2. The video seems partly misleading with all this talk of trying to get the cvt ratios properly calculated, but the pictures seem to show an off-the-shelf cvt from another application being used. I had thought from the beginning the builders actually manufactured the cvt. As someone with basic cvt experience from 3 different scooters (Helix, Tmax, and Aprilia BV250) I can tell you it’s not rocket science. You can dramatically change the characteristics on most stock cvt’s, meaning getting in the ballpark is fine enough, it’s all the after tuning that is truly important. Even listening to the bike at 8:50 my impression is that the lower rpm tune of the cvt is super conservative and the clutch engagement rpm is a lot lower than I’d ever want on such a bike. It’s cool, but I’m not sure why the builders found this aspect such a challenge.

    Btw, the YouTube video is from 2018.

    • That’s not our Youtube video. Just one the builder shared with us so readers could get a taste of the bike in action.

      • Yes, I hear you, just stating that so people have a sense of when the bike was built. I first saw the video and thought, wait, I’ve seen another bike with that rear suspension, so it can’t be that unique? Then I realized the video was from 2 years, ago, so I’m pretty sure the other bike was using this builder’s rear suspension design.

  3. Actually, here’s one bike that also has “horizontal rear suspension:” https://www.pipeburn.com/new-york-state-of-mind-bmw-k1100rs-by-marek/

    And this one is not the prior one I saw that had that suspension. Seems a good thing, thanks to Restrorides there seems to be a movement spawning for bikes with these conversions.

    • You’re right. I actually saw that Gustavo shared that one on his own account — he knows the builder. There seems to be a real community growing around the K-series bikes.

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