Erik Buell, founder and Chief Technical Officer of the motorcycle company that bears his name, has never been one to stand still. His diligent team of engineers and designers have garnered hundreds of patents for the development of their air-cooled race bikes. While that might be enough to please just about anyone, Buell knew that his company—which is owned by Harley-Davidson—had to make a significant change if it wanted to gain mass appeal in the sports bike market. Harley has been providing Buell with custom designed versions of its air-cooled V-twin engines since its inception in 1993 and that has posed a problem for the sports bike manufacturer—not that it was sourcing from Harley, but what it was getting. Sports bike aficionados eschew air-cooled engines because they lack power and reliability due to the need of a constant flow of air to manage heat dissipation. Liquid-cooled motors can operate at top performance regardless of riding conditions.
Buell didn’t want to just develop a liquid-cooled engine to satisfy his company’s customers, but he wanted to set new benchmarks in performance and innova-tion. Harley already had its liquid-cooled Revolution engine, developed with Porsche Engineering for the 2002 V-Rod, but Buell wanted something more compact. Knowing that his relatively small team would be unable to design, engineer and manu-facture the engine itself—not to mention the fact that Harley was busy developing its next-generation engines and products—Buell turned to Porsche Engineering and BRP-Rotax (who supplies motorcycle engines to Aprilia and BMW) to submit proposals on what they could bring to the table in terms of development resources.
“We talked to a number of people about the project. Porsche was a possibility, but we were all impressed with the Rotax team’s style. Their way of thinking was a significantly better fit than Porsche’s was,” says Buell, who dedicated five of his design engineers to the 3.5 year project that eventually resulted in the Helicon engine: A compact 72° 1,125-cc V-Twin producing 146 hp at the crankshaft. “The 72° angle turned out to be the best compromise for packaging. We considered a 90° but that packaging was too difficult to work within our chassis design,” Buell adds.
The Buell engineering team laid out specific requirements for the overall weight and power band, as well as the design of the crankcase, clutch and shift mechanism. Each is closely related to the chassis design. Rotax, meanwhile, worked on engineering the engine’s internal components and transmission configuration. Among the key attributes of the Helicon:
- The 72° angle allows the engine to be located far forward in the chassis, helping to limit weight distribution to 54% on the front tire, while reducing vibration.
- Three balance shafts: Two designed to cancel primary rotating imbalance and a third to cancel the rocking couple.
- Displacement: 1125 cc chosen for optimal 103-mm bore and 67.5-mm stroke for better breathing and reduced friction, resulting in increased rpm (redline: 10,500 rpm).
- Dual overhead cam design features a self-adjusting chain drive on each cylinder to the intake cam, and gear drive from the intake to the exhaust cam. Less space is needed over the cylinder head when compared to a two-sprocket design, and overall weight is reduced.
- Valves actuated with finger followers adjusted with shims, a design commonly found in Formula 1 engines and used in various diesel engine applications. This results in lower friction and quicker valve opening, while eliminating valve float and providing for a steep valve angle of 18°. Magnesium valve covers reduce weight.
- Integrated dry sump oiling reduces internal windage losses, and an integrated oil reservoir on the lower left side of the crankcase helps to keep the engine compact.
Development of the Helicon’s piston and ring pack was particularly tricky, Buell says, because of the high durability targets established by the team: “We did a ton of FEA [finite element analysis] work on those pieces to meet the targets.”
The Helicon team made “significant breakthroughs” and have filed patents for the development of the break-away engine mounts on the frame and fuel tank that result in improved crash performance, along with the ECU-controlled fuel pump that modulates fuel delivery based on specific commands from the ECU. The rotatable mounting of the engine itself helps to improve the ease of serviceability of valves, and is awaiting patent approval. “The engineering team should be happy with what we have accomplished because none of these innovations are insignificant,” Buell says. “What’s most amazing is that we self-funded this engine without Harley’s help.”
Rotax has worked with Harley-Davidson in the past, providing engines for its military motorcycles, including the MT350E used by British and Canadian forces. Rotax also provides engines for watercraft, ATVs and snowmobiles made by its parent company, Bombardier Recreational Products.