Drive to the 5-speed transmission and shaft final drive was by straight-cut gears. Inside was a plain bearing, single crankpin bottom end connected to a pair of 10.5:1 pistons, driving the four overhead cams by left-and-right spur gears and HyVo chains. Absent was any pretense of cooling fins, just clean alloy cases and smooth cylinders. The Vision’s drivetrain created a uniquely new look, suspended from (and forming an integral part of) its triangulated steel tube frame. And to negate the primary vibration inherent in high-revving, narrow vee engines, a single counterbalance shaft was added forward of the crank. To ensure adequate fueling at low revs, the Mikunis featured accelerator pumps, and the cylinder heads included Yamaha’s YICS induction control system, to improve “swirl” in the combustion chambers and promote more efficient combustion. The Vision was all new in concept and execution: Its liquid-cooled, 552cc dual overhead camshaft 8-valve engine was well oversquare at 80mm bore by 50mm stroke, fed by a pair of honking 36mm Mikuni carburetors. Yamaha fired back with the 75-degree Virago 750 and XVR920 then in 1982 came the revolutionary 70-degree V-twin XZ550R Vision. Honda came first with the 80-degree transverse CX500. Why not try a narrow-angle twin - in spite of their association with heavyweight cruisers? Among the options considered was a 90-degree V-twin, employed to such success by Italian manufacturers. So why not try something different? Kawasaki and Suzuki pretty much stayed the course with their UJMs, while Honda and Yamaha tried new ideas. The Big Four found themselves in a standing-quarter-mile shoot-out every year. They were the sliced white bread of their day. In the late 1970s, every Asian bike maker built air-cooled, inline 4-cylinder bikes - lots of them, from 350cc to 1,100cc.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |