Un kit KRAUSER....

MOTO EURO: Airhead Ambush, The Krauser was the First BMW "K" Bike
Written by: Marty Cohen Moto-Euro Magazine
Charlotte, NC – 8/2/2007



Somehow, thirty years have slipped by since BMW's R90S first appeared on showroom floors. A departure from traditional German practice, the 898cc twin burst onto the scene with a hotted-up(Dell'Orto carbed) engine, low bars, and attractive new smoked gray or orange painted bodywork. An inspiring success, this clever “café tourer” radically changed BMW's image. The R90S certainly had a profound effect on Bill Hardy, whose xtraordinary pair of Ventil acht Krauser Specials highlight his Moto-Euro encore. The first ("A Hardy Collection" M-E Summer 2001) chronicled his large and diverse accumulation of Euro hardware, not all of which can be considered entirely original or accurate. "That'll never be as important to me as having fun stuff to ride," relates Hardy, a horsepower junkie who also keeps a hand in high-performance automobiles and aircraft. "A segment of the machines in my collection are kept or restored as original, because it's important to do that. Those bikes are history books and I'm proud of them, but there's more to it. It's good to mix it up, show a little innovation. I don't live in the past."

As it turns out, neither did Mike Krauser. Best remembered for his expansive line of hard luggage options, by the early '80s Krauser had nearly cornered the motorcycle accessory market. Looking to branch out, his desire to expand coexisted with his love and affection for all things BMW. Involved in both car and motorcycle/sidecar racing (where BMW has a rich history) Krauser and his chief engineer Willie Roth explored both street and track options for the opposed twin. Derived, but not copied directly, from then-current technology found in his BMW racecar, the 4-valve kit for the R100 promised more power and flexibility for the legendary twin.

Made available through Krauser's Specialty Products group, the kit enjoyed an initial wave of popularity that was quickly overshadowed by the release of BMW's fourcylinder K-series. "We were enthusiastic about Krauser," recalls Marty Cohen, who established his Iron Horse Motorcycles BMW dealership in the late '70s. "Many of our customers approached us for performance work, usually after they'd owned their bike for a number of years. We installed the Krauser kits and other mods for the street and track duty. When the K100 arrived, the focus changed and everyone wanted the multi.For a time, we lost interest in building hot twins."

That, as the story goes, is where Hardy entered into the equation. "Ten years after the K100," recalls Cohen, smiling, "Bill came in and re-introduced the idea of building a really strong Airhead twin. You know, throwing the whole kitchen sink in then finishing it off in classic R90S trim, his favorite BMW. I thought, 'Yeah, why not?'The time was right to build it."

Building performance Boxers continues as a passion shared by enthusiasts all over the world. Perhaps drawing inspiration from select BMW pre-war efforts,Werner Fallert's 170-degree, high cam,bevel drive 4-valve Boxer prototype appeared in 1978. Complete with a vertically split crankcase, blade-type conrods and a jutting, race-spec windage oil tray,the Fallert FM1000 confirmed the passion many held for the opposed design.In the late '80s, the German-based Handrich & Mayer BoTT racer featured both Krauser engine parts and a version of the tube space frame first seen on his MKM 1000 Special.No doubt enjoying strong ties with factory officials (the racer proudly featured script on its upper faring proclaiming "100% BMW"), by 1990 H&M was running a factory prototype (carbureted) R259 twin in a Nico Bakker alloy spar frame. The industry lost a giant when Krauser passed away several years ago. These facts, and more, leave little doubt the influence he had on BMW's future engineering.

Meanwhile, Cohen and his team at Iron Horse had gathered comparable amounts of information for building its version of a high-output Airhead. For the chassis, Cohen based each Special on the Nikasil/R100 from '81-'84, replete with its strengthened straight-tube swingarm, Brembo brakes, factory lightened flywheel and electronic ignition. Sport dampeners and Euro-police spec springs were slid into each fork leg, while a pair of battle tested Koni 7610Ps got the call for rear suspension duties. Finished in bright nickel, no additional side braces were fitted to the frame. "When building the first, we dubbed it the 'Arizona Hotrod' due to Bill's preference for straight roll-ons," says Cohen;"These aren't track bikes; they were built for fast, comfortable travel."



Krauser's mission was to address certain shortcomings in the venerable twin, with his focus directed toward the R100's antiquated two-valve head. The widely spaced included valve angle results in a deep (and less efficient) combustion chamber that is even more prone to detonation with today's poor quality fuel. BMW responded by lowering compression, resulting in less horsepower. Convinced the engine could reliably withstand a 20% power increase, the squatty Cosworthinspired blueprint allowed for more compression and a flatter piston crown, while the centralized spark plug made the combustion chamber more efficient. The benefits of improved breathing due to increased intake and exhaust valve mass was nothing new, even twenty-five years ago, but the design gave the Airhead new life. The kit consisted of two cast alloy cylinder heads and covers, complete with new cylinder studs, valves, rockers, springs, and upper/lower pushrods.Also included was a pair of lightweight Malhe pistons and wristpins, sized in OEM A, B or C bore dimensions. In July of 1982, the editors of Cycle bolted the $1500 kit to a stock R100 and noted a graphic difference in horsepower and torque, even improved fuel mileage. The ¼ mile time dropped .67 of a second (12.42 versus 13.09) while trap speed increased 8.27 mph (108.04 compared to 99.77). Their notes concluded by saying: "Every staffer who rode the knitted BMW came back impressed with its new found punch. Run the bike in fifth, slow for a car then just gas it to ME/71 SPRING 2004 pass. Never mind if you’re on a hill or two-up.It is, in a word, terrific." Despite the initial praise, opinion of the kit gradually turned sour.

Although making good on its promise of boosting output, it suffered from a lack of proper R&D, if not outright finishing. Claims of coil binding, excessive noise and oil usage followed rumors of porous alloy castings, giving potential buyers more reason to disappear. "Most of the complaints are valid," responds Cohen, who admitted he "scrapped some expensive bits" in learning what it took to build a reliable Krauser. "Most owners just threw them on, right out of the box, which is a mistake. Through proper preparation you can solve the binding problem, but you can't fit the BMW Sport cam unless you use different (or modified) springs, which are impossible to find." Cohen also noted the heads were shipped with both sides of the valve seating left unfinished. "We cut a 45-degree angle into the seat (the Krauser uses no pressed-in seat material) and finish it with a five-angle valve job. This procedure alone netted another 2mm-plus of clearance.

Trading notes with close friend and master builder/restorer, Perry Bushong, in Fort Worth also aided Cohen in his quest for building a no-fuss Krauser. "Perry told me the intermediate section of the bottom two-piece pushrod (required for the shifted geometry and angle of the rocker arms) were hollow and would fill with oil,"remembers Cohen. "So we popped the ends off and welded them together. Later, I switched to Loctite, which seems to work just as well." After setting deck height,(either fly-cutting the surface of the head or shimming) the assembly is run through by hand, then taken apart and measured using plasti-gauge to insure everything is correct. "This is what you have to do.Using this approach, we're able to build a durable Krauser engine," states Cohen.

Having a knitted R100S at my disposal for many years, I'm right at home on Hardy's tricked-out Boxer. Despite claims of increased top-end racket, I note little difference between the Krauser and a bone stock R100 while threading through the late afternoon bustle. Once clear, a short blast of throttle leaves the traffic in my mirrors. Twist harder and the tone from the stainless Staintune exhaust changes from a deep purr to a growling Messerschmitt-like wail. Trolling about, the engine is R/50 docile, but around 5K the Krauser begins to show its teeth, pulling hard all the way to an indicated 130 mph. "That's how it was designed," says Cohen, "these engines were balanced and blueprinted to a very exacting degree. When you get caught in traffic, they won't load up or act nasty."

As previously mentioned, no additional bracing was added to the donor R100 frame, nor were the slim upper and lower triple trees swapped for stronger aftermarket pieces. Our evaluation indicated they weren't needed, as both machines were rock steady well past the ton. Again, Cohen's experience in building motorcycles that work becomes evident. A stock R90S mounts its faring to the handlebar/upper triple tree, a method that was later discovered to cause a slight weave approaching triple-digit speeds. Cohen's solution was to fix the faring to the frame using the upper mount from a R100RS. While your eyes are there, note the placement of the headlight - it's flush with the front, allowing smoother aerodynamics. "That's a trick I learned from (former BMW Superbike crew chief) Udo Gietl," recalls Cohen. "The factory recessed the lens, making a turbulent 'pocket' that pushed the front end around. This application allows the faring to protect the rider, not upset the motorcycle."

On a calm, late winter afternoon the Publisher and I relax on artful Mill Avenue with a latte in
one hand, Krauser keys in the other. Posed majestically at the curb,our pair of Teutonic travelers incited their fair
share of attention. More than one passerby asked if the bikes were new,bowing perhaps to their classic style. Conversely, another 'purist' chastised us for 'butchering' such a collectable motorcycle.That's expected, but no actual R90Ss were harmed in the making of this film. In fact, except for the Krauser parts, one could easily duplicate Hardy and Cohen's vision with a mixture of new and used pieces, all of which are readily available. Hoards of R100s are still in use and can be purchased affordably, backed by a thriving worldwide aftermarket offering a diverse supply of specialty items.Now, long out of production, the Krausers occasionally pop up, but expect to pay a premium. If you do bag a kit, you know whom to call.

Our conclusion? Hardy's vision, Cohen's aptitude and Krauser's dedication have combined to produce a series of motorcycles that showcase the attributes of the original, accented with an alluring techno-twist. Beautifully finished, wellconceived and deeply rewarding to ride, Hardy's Iron Horse Specials rekindle a fire begun three decades ago. If you've fancied the idea of building a hot Boxer, look no further for inspiration. "If it wasn't for Marty," summarizes Hardy, "these bikes wouldn't exist, because I would not know they could." Consider us clued-in, along with the realization that the "fun stuff" is a result of talent, experience, and camaraderie.