From Kradhaus Bikes: Short-stroke BMW with a Kaczor racing frame…
In 1965, Ferdinand “Ferdi” Kaczor, a young engineer and motorcycle racer, designed and built his own chassis around the BMW R50/2 engine, creating a 500cc race bike to compete in the German Motorcycle Championship.
“He refined the [production] engine and doubled the output to 50 hp while cutting the weight with a special very light and rigid frame to under 300lbs.” -BMW Press Club
Kaczor was so successful on this 500cc racer that BMW hired him to work in-house, and he became one of the top German riders of his time. In 1969, Kaczor set a new lap record on the Nürburgring Nordschleife (“The Green Hell”) on this bike, beating the previous record set by John Surtees on a four-cylinder MV Agusta. This was just a few months before the German Grand Prix.
“None of the World Championship competitors, including Giacomo Agostini, was able to wrest his record.” –Motorsport Memorial
What’s more, Kaczor was renowned for his skills in the workshop.
“Regardless of which contemporary witness tells of ‘Ferdi’, everyone raves about his brilliant technical skill. ‘Ferdi even worked his camshafts by hand on the grinding machine,’ says Helmut Dähne, still deeply impressed today.” –Motorradonline.de
Kaczor began to produce a few of his special self-named Kaczor frames for racers and riders. Unfortunately, his life came to an early end during practice for the 1970 Austrian-TT, when he lost control of his machine on the approach to an S-bend in the village of Hollenstein. He was just 29 years old.
However, Kaczor’s name and designs lived on, and over the years, different builders have reproduced his lightweight frame design. One of these is our new friend Christoph Reintsch of Germany’s Kradhaus Bikes — a man who certainly has motorbikes in his blood.
“My great-grandfather was already on the road in his homeland Bohemia on an Indian before World War II.”
To this day, Christoph works in the shop with his father, Horst, and even his grandfather, Josef, and their private collection of bikes includes an enviable number of BMW, Ducati, and Honda models dating back to 1937.
Christoph has been building bikes since 2006, though the Kradhaus name didn’t appear until earlier this year. In 2020, Christoph and crew got their hands on a frame gauge, and now they are producing racing frames in the Kaczor and Dähne styles.
The Kaczor R60/7 you see here was built for Kradhaus Bikes team member Marlene Mößbauer, who wanted a lightweight machine with good performance that would be suitable for her stature. The standard Slash 7 frame was modified in the Kaczor racing style, and accompanied with shortened Kawasaki Zephyr forks, 18-inch R45/65 cast snowflake wheels, front double disc brake, Benelli Mojave tank, Moto Guzzi fairing, and more.
The engine was heavily breathed upon as well. Highlights include modified R100 heads, lightened pistons / con rods / valve train, electronic ignition, twin 38mm Dellorto carbs, 2:2 Hattech exhaust, and a lightened single-disc dry clutch.
The result is a street-legal BMW café racer that weighs just 161kg wet (355 lbs), with 75 hp and 60 lb-ft of torque out of the quick-revving short-stroke engine. Says Christoph:
“The whole bike was reduced and slimmed down only to what was necessary. This results in the radical and very slim line. The light weight in combination with the high-turning short-stroke motor is a super combination.”
In a world where too many BMW airheads are modified more for style than substance, this is a two-wheeled Bavarian hot rod that’s extremely well designed and executed, and it establishes Kradhaus Bikes as a workshop to watch. We have no doubt that Ferdi Kaczor would be proud.
Below, we talk to Christoph and team for the full details and build sheet on the build.
Kradhaus Bikes: Builder Interview
About the Builder:
Christoph Reintsch
- Born on 25.07.1990
- Resident in 92712 Pirk
- Mechanical engineer at ZF Friedrichshafen
Passion for motorised, old two-wheelers was basically strongly rooted in my genes. I usually work on the projects with my father Horst (27.01.1959), but my grandfather Josef (20.12.1937) also supports me wherever he can. My great-grandfather was already on the road in his homeland Bohemia on an Indian before World War II.
For as long as I can remember, I have been riding with my grandfather on his BMW R100S as a passenger.
Our private collection of old motorbikes includes BMW and Ducati between 1937 and 1993 (BMW R20 / R66 sidecar / R25/3 sidecar / R60 sidecar / R75/6 / R90S / R100S; Ducati 900 SS Königswelle, Ducati 900 SS; Honda Dax ST50, Honda Dax St70).
Thanks to our well-equipped workshop with lathe and milling machine, almost all parts are manufactured by us in meticulous detail work. The parts are sketched, prototypes are made by ourselves or 3D printed and, if necessary, designed on the computer and then CNC manufactured. All parts are also blasted and powder-coated ourselves (as long as they fit in the oven). We also repair and optimize motors and gearboxes.
The frames we use are tested, straightened, and fabricated on the frame gauge beforehand. For the welding work we have support by a mate of my father. The frame gauge has gradually expanded. So far the frame building of the racing frames Kaczor, Dähne, and soon also central tube frames is possible. The straightening of all 2V Boxer frames from 1936 on is possible and practiced.
In events I am an exhibitor mostly with the company Hattech on the way. The bikes are mostly assembled from single parts, therefore the takeover of the parts collection of Anton Hötzinger from Plattling was more than reasonable.
To give the child a name, the label KRADHAUS was founded in 2023, which is now being built up bit by bit.
Personal milestones:
- 2006-2007: Yamaha XT 125 – Supermoto modification
- 2011-2012: Honda Dax – Restoration / modification
- 2012-2013: Ducati 900SS Königswelle – Caferacer modification
- 2013-2014: Husqvarna SMR 630 – Supermoto modification
- 2015-2016: BMW R51/3 – complete bobber modification
- 2017-2019: BMW R75wh – Complete Racebobber modification
- 2019-2020: Yamaha XV535 Virago – Chopper modification
- 2020: Take over frame gauge of Anton Hötzinger
- 2020-2021: BMW R90/6 in Dähne frame – complete build-up Scrambler
- 2021-2022: BMW R60/7 in Kaczor frame – complete construction Caferacer
- 2022: Takeover of the complete Anton Hötzinger parts collection
- 2022-2023: Fiat Ducato – Motorcycle camper conversion
- 2023: Foundation of the “KRADHAUS” label
About the Bike:
The second project with self-modified frames. This and the Dähne frame were built in parallel.
The idea was to generate a suitable bike with performance and good chassis / technology for my friend Marlene. She was enthusiastic about riding the Scrambler, but her legs are a bit too short for it. The bike is extremely fun even with my height, but unfortunately it looks like a pocket bike underneath me.
The decision-making process on the colour scheme was very long and grueling. However, I let myself be persuaded and am very happy with the final result.
The whole bike was reduced and slimmed down only to what was necessary. This results in the radical and very slim line. The light weight in combination with the high-turning short-stroke motor is a super combination. As with the other projects, a clean look is very important to me.
Final carburettor tuning is now complete with the help of a lambda tester to ensure the best possible tuning across the range.
Build Sheet
Kaczor Project – BMW R60/7 (1979)
Engine:
- Four-stroke two-cylinder boxer engine, air-cooled, two valves per cylinder
- engine housing type R45 / R65 lightened
- asymmetric camshaft, bore x stroke 94.0 x 61.5mm, displacement 854ccm, compression ratio 10.0:1
- cylinder heads type R100, modified
- lightened pistons and connecting rods
- valve train lightened, lighter valve adjustment screws, tappets lightened
- Silent Hektik type electronic ignition
- Two Dellorto PHM carburettors Ø38mm, with short intake funnels
- Lightened single-disc dry clutch
- 2in2 Hattech complete system “Sidepipe GB25”
- Five-speed gearbox type /7, 34/11 cardan
Power: maximum approx. 75 hp (55kW) at 6150 /min, torque 82 Nm at 5500 /min.
Chassis:
- Standard frame /7 modified after Kaczor racing frame,
- Front fork type Kawasaki Zephyr 750, shortened with progressive fork springs, standpipe Ø41mm
- triple clamps type K75S with integrated speedometer
- stub handlebars
- Rear standard swingarm type /7, shocks IKON TYP 7610
- 18 inch cast wheels type R45/R65
- Front tyres 90/90-18, rear tyres 110/90-18, type Conti ClassicAttack
- Front aluminium wheel cover
- front double disc brake Ø300mm, rear simplex drum brake Ø200mm
- Wheelbase 1460mm, seat height approx. 740mm
- Tank type Benelli Mojave, tank capacity 10 litres
- hump seat GFK, handlebar fairing shortened type Moto Guzzi Le Mans II
- Footrest system moved back
Weight: full tank / ready to ride 161kg
Time commitment: September 2021 to May 2022. Approx. 850 h
Follow the Builder
KRADHAUS – Bavarian Custom Bikes
Christoph Reintsch
Media and marketing: Marlene Mößbauer
Web: www.kradhaus.de
Instagram: @kradhaus_bikes
Facebook: Kradhaus Bikes
The pubs must be getting desperate these days. Some of the “builds” l (like this) being posted are atrocious. I get that beauty is in the eye of the beholder and all that, but only to a certain degree. If you have no design aesthetic, don’t design things.