|Return to GR650 Presse||reprinted from the May 1983 issue of Cycle Magazine|
The 650 vertical twin should be dead and long forgotten. It's not. Suzuki engineers have lifted the concept from the history books, marched the configuration through computers, given it a variable-mass crankshaft, a counterbalancer, an air-swirl induction system and oil-jet cooling, and mounted the entire package in a single-shock chassis. Applying new technology to an "old" configuration has produced a freshly minted motorcycle with contemporary performance. Without this reapplication of new engineering, old concepts stay old. New tech revived V-engines, and now Suzuki has remade the 650 vertical twin.
When you look at the GR650D's engine you'll understand how ideas and technology produce compact, efficient powerhouses - a 650 engine that's 450-small. The Tempter's central crankcase castings, for example, are 35mm shorter and eight millimeters narrower the the GS450's, even the GR's cylinder head is just seven millimeters wider. The GR's overall sump-to-cam box height is only two inches more than the GS650 transverse four engine, yet the GR has a cylinder head with half the moving parts and a much-condensed lower end. Suzuki engineers pressed and compressed the 650 engine into the smallest, tightest package manageable.
Central to the machines nimble handling is the GR's compact engine. Suzuki's Full Floater suspension positions the single shock absorber directly between the engine and the rear wheel. Carrying the hefty shock unit and its accompanying linkage low, near the swing-arm pivot, drops the bike's center of gravity. The GR's 56.3-inch wheelbase (the same as the GS550ED's and shorter than many other 550s' and 650s') is in part responsible for the GR's quick, light handling; that short wheel span would be impossible with a long engine block. In motion, the bike steers like a 550; at a stop, it feels even smaller - like a 450.
The engine's compactness adds other benefits. A narrow engine can settle lower in it's chassis without limiting ground clearance, in turn lowering the bike's center of gravity and center of mass. A compact, light engine allows lighter superstructures; the frame, swingarm and connecting hardware all reflect this. Diet engineering pays off: The GR650 weighs 438 pounds with a full fuel tank, moving the Tempter closer to the 450 twins than the 650 in-line fours. It's even lighter than bikes from that champion marquee of engineered weight savings; fully gassed, the GR presses it's rubber against the payment some 13 pounds less than BMW's lithe R65LS. The final result is a motorcycle with 450 feel and 650-twin punch.
The 650's engine internals also ran through the engineering weight-reduction salon. The camshafts are hollow-bored, according to Suzuki sources a first for the company. Power from the crankshaft drives the clutch via helical-cut gears, runs through the five-speed gearbox, then goes directly to the rear wheel by a #530 roller chain. The 650's drive train contains no heavy, power-wasting jackshafts, transfer boxes or driveshafts. The cam-chain tensioner, a simple coil-spring unit, is similar to DR and SP types. Suzuki engineers used computer analysis to delete excess material from the crankcase castings.