Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/127937
RTV1200 Black Widow Within the cast-iro.n sleeves of the CNC-machined alloy cylinders run Australian-made billet connecting rods carrying three-ring JE pistons delivering 8:1 compression - low enough to ensure that the RTV can run on regular unleaded fuel, especially with the hardened valve seats and stainless-steel valves, all of .which (two per cylinder) are the same sizes as in the original, smaller-capacity engine. "The. one-liter Vincent was always over-valved," says Prince, "so now it's correct for a 1200 motor. But though Irving's design was a masterpiece by any standards, let alone for 60 years ago and we've retained the same 65-degree included valve angle in redesigning the heads - .we've increased flow by as much as 40 percent on the' new cylinderhead design." The many changes incorporated in this - while still retaining the overall format with short pushroc\s worked by the redesigned cams high-set in the crankcases - include increased fin area for extra cooling, a hemispherical combustion chamber (that incorporates a squish band not found on original Vincents), a more-rational oiling system (but still incorporating the same design of double-delivery oil pump as in the older motor), and stronger seats for the cylinder studs and engine bolts to deliver a stiffer structure (which is important with the engine a fully stressed ~assis member). The engine also features a revised valve gear as part of an overall redesign of the timing side that Prince says were often a weak point of stock Vincents. There is also provision for later fitting of the MicroTech fuel injection Prince has under development, in the form of cast-in bosses that can be machined for the injectors, etc. There are also much-larger inlet and exhaust ports, including the D-shaped ones that their fellow Aussies at Vee Two use on their two-valve Ducati heads (as does Prince on his tuned Vincents), which have already proved to deliver more performance. With primary drive provided by triplex chain, and a crank-driven alternator housed in the primary case that powers the RTV Hall-effect electronic ignition with fully programmable curve, power is transmitted via a heavily beefed-up multiplate clutch to the RTV's all-new five-speed gearbox - not one of the original Vincent four-speeders with an overdrive fifth fitted, but an all-new cluster. "Realistically, the engine has so much torque it doesn~t need this," admits Prince, "but fashion dictates what the market wants, so here it is." More to the point, perhaps, the all-. new transmission resolves one problem of the old engine, whereby it was impossible to fit a rear tire any bigger than a l30-section without fouling the drive chain. Offsetting the gearbox sprocket 20mm via a new castjng housing aI)d outrigger bearing means more space, plus a stiffer, stronger mainshaft assembly - needed for the 90 bhp at 6500 rpm which the RTV1200 engine is claimed to deliver at the gearbox. That's a big step up from the 55 bhp at 5700 rpm of a late Black Shadow, or even the 70 bhp of a more radical Black Lightning racer. "The chassis sort of designed itself," said Prince. And he should know. After all, his experience in building the Egli-based forerunners of the RTV means that he knows what worked, so he opted for the same spine frame design (with the largediameter .tubular-steel backbone dou- bling as an oil tank for the dry sump engine - which is underslung from it, acting as a fully stressed chassis member). Wheelbase is a contained 1420mm, and while the 26.5-degree head angle for the Paioli upSide-down forks and 105mm of trail wouldn't be accused of delivering radical steering geometry, the idea was to build a modern classic rather than a racer with lights, says Prince. By those standards, the styling by Bike Art's Richard James, who has also worked on the Hunwick Hallam project, which emp1