A chain drives the intake cam, while a separate gear drive connects to the exhaust cam. Note the use of stick coils, and the offset between the cams-the exhaust cam sits slightly lower than the intake, opening up room on the intake side for a straighter, larger port and saving space on the exhaust side to shorten the motor's overall length.
The 72-degree V angle was chosen to optimize packaging, as it allows the straightest intake path from throttle body to valve without crowding the throttle bodies between the Nikasil-plated cylinders and also minimizes the length of the engine front-to-back. The dry-sump design utilizes a partition in the crankcase to store the oil rather than an external tank (or the swingarm, as used in the XB models).
Rather than use a cush drive in the rear wheel (adding unsprung weight), the 1125R has a "compensated" front sprocket to absorb driveline shock and reduce wear on the belt. As on the XB models, the Goodyear Hibrex belt needs no adjustment or replacement. The belt drive is now on the left side, opposite to the XB's layout, and the new transmission is a six-speed versus five.
The large diaphragm controls the clutch, reducing lever effort and adding a slipper effect by using vacuum to disengage the clutch. Conveniently, engine vacuum is high at idle-reducing lever effort by approximately 20 percent-and also on closed throttle, providing more slip at higher rpm. The setup is similar, if not identical, to the system used on the Aprilia Mille engines. Oil is evacuated from the crankcase through the clutch cover using vacuum, reducing windage losses. The water pump, just above the crankshaft here, incorporates one of the three balance shafts on its gear. A second balancer is seen here just below the crankshaft.
Rather than using a shim-under-bucket layout, the Helicon engine has finger followers. The followers allow adjustment without removing the camshafts, although the 1125R's engine must be lowered to access the front valve cover. This arrangement helps close up the included valve angle to a shallow 14 degrees, in turn making the combustion chamber more compact.
The third balance shaft is located on the rotor side of the engine, just above the crankshaft. Two counterbalancers reduce the inherent primary imbalance of the 72-degree layout, while the third accounts for the rocking couple created by the side-to-side offset of the cylinders (the width of a connecting rod). Ironically, the XB engines have a knife-and-fork connecting-rod setup, with no rocking couple.
Huge 61mm throttle bodies are quite short, with the injectors (one per cylinder) located downstream of the butterflies (also one per cylinder) and aimed almost directly at the intake valve. An elliptical cam varies the throttle actuation for more control at small openings and a shorter throw at larger openings.
Like the XB models, the 1125R's swingarm pivots in the rear of the crankcase. But whereas the unbalanced Sportster-based engine of the XBs was installed with a system of dampers and links to reduce vibration, the new bike's balanced mill can be solidly mounted to the frame to reduce complexity and increase stiffness. The frame/fuel tank is larger than previously, with more fuel (5.6 gallons, up from 3.8 gallons) and 57 percent more stiffness. While rake and trail are identical to the Firebolt's numbers, the wheelbase is 2.5 inches longer, with the shorter engine extending swingarm length by even more than that. While the Firebolt and Lightning frames were made in Italy, the 1125R frames are built in Wisconsin.
The updated ZTL2 (Zero Torsional Load) brake has an eight-piston, four-pad caliper developed from the XBRR program. Increased chassis stiffness and more braking power called for a beefier front fork, and the Showa's tube diameter is now 47mm, up from 43mm. Grippy Pirelli Diablo Corsa III tires are standard, and worked great on both the street and track portions of the intro.
The radiators mount to the engine, with flexible brackets and shrouds protecting them in a tip-over. The mounting arrangement frees up space to move the engine as far forward as possible. Internal vanes direct air in from the shroud side and then through the frame and over the engine for additional cooling. This view shows the ram-air inlet, stainless steel brake line, dual exhaust outlets per cylinder, and the O2 sensor used in the closed-loop EFI.
The fuel-in-frame layout opens up more volume for the airbox, just as it does for the Firebolt and Lightning models. But where the XBs breathed through a side-mounted intake, the 1125R has a duct leading to the high-pressure zone under the bottom triple clamp.