Honda CB 650F

This Honda CB650Fnaked streetfighter is powered by a 649cc inline-four, the Japanese company’s third new engine in three years. Key design features of the powerplant include cylinders canted forward 30 degrees, a 16-valve DOHC cylinder head with direct cam actuation, PGM-FI fuel injection (working with 32mm throttle bodies), and connecting rods optimized in length to minimize side forces on the pistons, which have asymmetric skirts to further reduce friction. What’s more, breathing holes in the crankcase walls between the journals reduce pumping losses as rpm rises.

Honda says the oversquare engine, with a 67.0mm bore and a 46.0mm stroke, is tuned for good torque below 4,000 rpm and great midrange roll-on throttle response. Yet the CB650F engine can also rev, with a claimed 86 hp arriving at 11,000 rpm and a peak torque value of 46 foot-pounds reached at 8,000. And thanks to internal water channeling from head to cylinders, the number of hoses has been reduced, giving this Honda engine a clean, uncluttered appearance that can be appreciated from its highly visible spot beneath the bike’s minimal fairing, where the aforementioned headers are also display. Honda, interestingly, placed the oil cooler on the left front and the oil filter on the back of the engine to help accommodate those cool 4-into-2-into-1 pipes, which sweep back to the right and flow into a stubby underslung muffler that helps with mass centralization.

The CB650F chassis—a twin-spar arrangement designed to be extra stiff around the headstock and a bit “flexible” down by the spars—has cast pivot plates, a 41mm Showa fork and a conventional aluminum swingarm acting directly on a single shock. Moreover, Honda says the bike—which has twin 320mm front brake discs and a 240mm rear with standard ABS—has a slim feel, and the high-set handlebars are designed to give riders, especially beginners, excellent confidence and control on the bike, which has a claimed curb weight of 454 lb., a rake of 25.5 degrees and 3.98 inches of trail.

Features

CB650F Torque: 46 lb-ft of torque at 8000 RPM (63Nm).

The CB650F’s liquid-cooled engine uses compact internal architecture, stacked six-speed gearbox and starter/clutch layout with the four cylinders canted forward 30°. The DOHC 16-valve cylinder head employs direct cam actuation and cam timing that equals strong torque performance and drivability below 4,000 RPM.

Bore and stroke is set at 67mm x 46mm. Optimisation of con-rod length has decreased the side-force on each piston and ‘breathing’ holes in the crankcase walls between the journals reduce pumping losses as RPM rises. The pistons were developed with Computer Aided Engineering (CAE) and asymmetric skirts minimise bore contact and reduce friction. Ferrous spines on the outer surface of the cylinder sleeves reduce oil consumption (and friction) with improved heat transfer.

A silent SV cam chain reduces frictional losses by using a Vanadium coating on its pins and the water pump – designed with CAE study of water flow – is compact, light and efficient.

The engine is smooth at all rpm, with distinct inline four-cylinder character and resonance.

Internal water channeling from cylinder head to cylinders does away with a great deal of the exterior hoses normally required and the motor shows off its minimal, elegant beauty and functional style. The layout of the oil filter (behind the engine) and oil cooler (front left) plus internal oilways further enhance the visual appeal and has enabled use of an evocative right side-swept 4-2-1 exhaust.

With strong echoes of the original Honda 1974 CB400 / 4 the design employs optimised downpipe length and diameter, plus patented internal plates regulating airflow to improve torque. The ‘wafer’ design stubby underslung muffler – with 400-cell catalyser – contributes to mass centralization.

PGM-FI fuel injection is fed through a down-flow airbox and narrow 30mm high-velocity funnels, with intake gas flow routed in as straight a line as possible. It operates with information from four separate throttle body sensors on 32mm throttle bores for crisp and accurate throttle response. Careful siting, position and angle of the throttle bodies allow a narrow frame width, improving manageability for the rider.

To deliver good fuel economy at constant throttle (cruising at higher speeds) short valve overlap timing works with a specific ignition map; fuel consumption of 21km/l (WMTC mode) gives over 350km range.

The steel diamond frame uses twin 64mm x 30mm elliptical spars. Its rigidity balance has been specifically tuned – it’s much stiffer around the headstock and more ‘flexible’ in the spar sections – to deliver the desired handling characteristics and level of rider feedback. Rake is set at 25.5° with trail of 101mm and wheelbase of 1,450mm. Curb weight is 454 lbs (ABS: 458 lbs).

The swingarm pivot plate is forged then welded together, while the gravity die-cast aluminium swingarm features a curvaceous shape that arcs over the muffler on the right. Adjustable for 7-stage spring preload the single-tube monoshock operates directly on the swingarm. Both the rear shock and 41mm telescopic fork (with 120mm stroke) have been developed to work directly with the frame’s performance dynamics to provide supple, neutral control in all conditions.

Cast aluminum six-spoke wheels wear 120/70-17 and 180/55-17 front and rear radial tires. The wave brake rotor discs use the same manufacturing technique as the twin-cylinder NC750 series: the 240mm rear is formed within a 320mm front, saving material (and ultimately cost) to the customer. The two-piston front calipers and single-piston rear provide plenty of stopping power, with 2-channel ABS an option.

A ‘Mass Forward’ stance with minimal front and rear overhang gives the CB650F its muscular appearance, hunched and ready for action. The short fuel tank, shroud covers and sharp nose fairing add dramatic presence as does the stubby, shrink-wrapped upswept tail unit. Hinged at the back, the tank allows easy access to the cylinder head for maintenance. Both taillight and front position lights are LED and the headlight uses the distinctive ‘CB’ V-shape.

The riding position is naturally upright and slightly forward, placing the rider close to the bike’s centre of gravity. High, wide tubular handlebars give leverage and pillions get an ample seat and strap for security. Seat height is 810mm and the narrow middle profile helps ground reach.

The dash comprises twin large digital screens. On the left are the rev-counter and speedometer; on the right are a fuel gauge, clock, odometer and the warning lights. Both sides are lit by a white back light. A compact ‘wave’ design ignition key offers improved security and reduced chance of breakage.