The 1125R Helicon engine is Erik Buell's first liquid-cooled, non-Harley-Davidson powerplant since his original Barton-powered two-stroke RW750 roadracer in 1984. It was designed in collaboration with and built by BRP-Rotax in Austria and, as expected, incorporates plenty of forward-thinking technology. The 1125cc displacement is achieved via radically oversquare dimensions (103mm bore/67.5mm stroke), making room for big, 41.3mm intake and 35mm exhaust valves. Cylinders are splayed 72 degrees apart, a figure chosen because it provides a steep, 18-degree valve angle and the straightest possible flow path for the downdraft intake system, which is capped with dual 61mm throttle bodies managed by H-D's own DDFI 3 EFI technology. Dual overhead cams are operated by a combination chain/gear drive with a self-adjusting chain spinning the intake cam, which in turn drives the exhaust cam via gear-making for a more compact cylinder head, reducing engine weight and allowing the motor to be mounted farther forward in the chassis. Valves are actuated via finger followers (technology borrowed from Formula 1 racing) to reduce friction, provide quicker valve opening and virtually eliminate high-rpm valve float. To control vibration, the engine is fitted with no fewer than three balance shafts: two to cancel primary rotating imbalance and a third that cancels the rocking couple. Dry-sump oiling reduces internal windage losses, and oil is held in an integrated oil reservoir in the lower left side of the crankcase-not in the swingarm, as on the air-cooled XBs. A single large-volume muffler wraps around the bottom of the engine; careful tuning provides linear power delivery without use of an exhaust valve, and the muffler incorporates a Helmholtz chamber to reduce noise. All major engine components are unique to Buell, and the engine will not be shared with other brands or used to power any other recreational products.
Like any proper sportbike, the 1125R gets a stacked, close-ratio, six-speed gearbox complete with straight-cut gears operating on a sliding-dog mechanism for smooth, light shifting action. Attached to the output shaft is a compensated sprocket that essentially acts as a cush drive at the engine instead of at the rear wheel, another clever engineering solution that further centralizes mass and reduces unsprung weight.
Buell says the American-made "Intuitive Response" frame is its stiffest yet. The main spars of the fuel-bearing structure are even more massive than those of the XB, and that extra space is put to good use to hold an additional 1.8 gallons of fuel, raising total capacity from 3.8 to 5.6 gallons. The new frame has been optimized for torsional stiffness to better resist side loading in corners, aided by a solid-mounted engine that serves as a stressed chassis member. The swingarm mounts directly to the engine cases to minimize chassis width and create an even more rigid connection between the rear wheel and frame. The arm is also more than 2 inches longer than the XB's, increasing the wheelbase from 52 to 54.6 inches to better resist wheelies in light of an added 50-something horsepower. Front-end geometry remains identical to that of the XB with a steep 21 degrees of rake and 3.3 inches of trail.
The HVA (Hydraulic Vacuum Assist) clutch utilizes vacuum pressure generated within the intake manifolds to assist clutch action for reduced effort at the lever and to provide a "slipper" effect. At open throttle vacuum pressure in the intake manifold is low, which results in full clamping loads on the clutch plates to minimize slippage and maximize forward acceleration; at closed throttle the manifold pressure increases, leading to lower pressure on the clutch diaphragm and effectively reducing clutch clamping load, which lets the clutch slip slightly to reduce engine braking and rear-wheel chatter during aggressive downshifting.
The plus-sized, 47mm Showa fork-one of the fattest ever fitted to an OEM sportbike-was a necessary upgrade, as the slimmer, 43mm XB fork would be overpowered by the new, stiffer frame. The triple-clamps (handlebars are integrated into the upper clamp) have likewise been stiffened, and the fork is fully adjustable. The piggyback-reservoir shock is also sourced from Showa, and is likewise fully adjustable. The shock mounts horizontally to make room for the muffler below, and is acted on directly by the swingarm without benefit of a linkage, relying instead on a progressively wound spring.
Up front resides a bigger, brawnier version of Buell's signature ZTL2 (Zero Torsional Load) braking system, featuring a massive eight-piston caliper borrowed from the XB-RR racebike. The caliper casting is optimized for rigidity and heat dissipation, and four pads clamp down on a 375mm, stainless-steel "inside-out" rotor that bolts directly to the wheel rim to reduce torsional loading. Buell claims its single-sided system saves as much as 6 lbs. of unsprung weight compared to a conventional, dual-disc set-up, reducing steering inertia. The rear brake consists of a 240mm stainless rotor acted on by a two-piston caliper mounted directly to the backside of the swingarm, sans carrier, to save another claimed 1.5 lbs. of unsprung weight.
The 1125R marries innovative technology proven on the XB series (Zero Torsional Load brakes, Immediate Throttle Response belt drive, fuel-bearing frame, etc.) with an all-new, pivotless frameset and a liquid-cooled V-twin built by Rotax.
A worthwhile addition to the large-capacity sport-twin category currently occupied by Ducati's 1098 Superbike, Aprilia's various RSV1000Rs, the BMW R1200S and, to a lesser extent, Suzuki's SV1000S.
Engine type: l-c 72-deg. V-twin
Valve train: DOHC, 4v
Bore x stroke: 103.0 x 67.5mm
Fuel system: EFI
Clutch: Wet, multi-plate slipper
Frame: Aluminum twin-spar
Front suspension: 47mm Showa inverted cartridge fork, adjustable for spring preload, compression and rebound damping
Rear suspension: Single Showa shock, adjustable for spring preload, compression and rebound damping
Front brake: Single ZTL-type eight-piston caliper, 375mm disc
Rear brake: Single two-piston caliper, 240mm disc
Front tire: 120/70ZR-17 Pirelli Diablo Corsa III
Rear tire: 180/55ZR-17 Pirelli Diablo Corsa III
Rake/trail: 21.0/3.3 in.
Seat height: 30.5 in.
Wheelbase: 54.6 in.
Fuel capacity: 5.6 gal.
Claimed dry weight: 375 lbs.
Claimed horsepower: 146 bhp @ 9800 rpm
Claimed torque: 82 lb.-ft. @ 8000 rpm
Color: Midnight Black w/Diamond Blue frame
Available: November 2007
Warranty: 24 months, unlimited mi.
Contact: Buell Motorcycle Co.
2815 Buell Dr.
E. Troy, WI 53120
Too soon to tell-we need to ride a production-ready version before passing judgment. The 1125R has the potential to be a breakthrough bike for Buell, provided the company addresses a few key pre-production glitches.