HONDA XR650 R

TECH STUFF YOU MIGHT WANT TO KNOW

This is the most powerful engine ever in a Honda XR; it's a liquid-cooled 649cc SOHC four- valve dry-sump engine. The single-backbone aluminum frame represents the next evolution in off-road aluminum chassis technology.

Kayaba suspension components replace the old Showa units. The package provides a combination of comfort and plushness, with excellent control and performance. A 46mm front fork is matched to the 44mm fully adjustable long-stroke piggyback rear shock absorber.

Optional competition parts increase horsepower and torque an incredible 27 percent!

ENGINE

• The all-new liquid-cooled four-valve SOHC 649cc engine is compact, and weighs only 88 pounds.
• Dry-sump oiling system includes an in-chassis oil tank.
• The engine design separates the crankshaft and generator rotor from the engine oil that causes windage resistance, allowing for a freer-revving engine.
• Nikasil cylinder lining is lightweight and provides cooler and quieter operation for extended engine life.
• 37mm intake valves and 32mm exhaust valves provide increased engine efficiency.
• An automatic decompression starting system, with handlebar-mounted compression- release, makes for relatively easy starts.
• New 40mm carburetor delivered crisp response and excellent rideability.
• Solid-state CD ignition with electronic advance.
• Gear-driven counterbalancer for engine smoothness.
• Maintenance-free XR400-type automatic cam-chain tensioner.
• Dual aluminum radiators for optimum cooling and maximum performance.
• Free-flowing two-into-one stainless steel headpipes.
• Primary kickstarting allows start-up in any gear.
• Extended kickstart lever and a new reduction ratio allow for a slow, strong kick to spin the engine quickly for starts.
• Lightweight magnesium clutch cover provides easy access for maintenance.
• Improved shifting five-speed transmission.

POWER

A huge part of the XR600R's appeal has been the quality and quantity of its power. Still, XR owners have always figured more is better when it comes to horsepower. So, when the XR650R design process began, more horsepower was at the top of Honda R & D's shopping list.

To meet power and durability goals, more displacement was a given. Testing various intermediary engine sizes revealed a 649cc single-overhead-cam four-valve single delivered the perfect balance of power, torque and toughness. Since more power means more heat, liquid cooling was a given as well, opening the door for all-new engine architecture from the cam cover down.

Gone is Honda's familiar Radial Four Valve Combustion (RFVC) system, with valves splayed radially around the bore axis. The XR650R uses a lighter, simpler, more effective overhead camshaft system, above a flat combustion chamber that's fired by a single spark plug.

Mixture from the 40mm Keihin carburetor enters via a pair of 37mm intake valves (up l mm from the 600), and exits through 32mm exhaust valves (also l mm over XR600R spec). These valves are controlled by a cam with more lift, overlap and duration than an XR600R's.

Just below, the 650's Nikasil-lined aluminum cylinder moves closer to vertical than the old bike, creating more space for the twin aluminum radiators. This more upright engine position also shifts the crankshaft center closer to the front wheel to help optimize weight distribution.

Both the l00mm bore and the 82.6mm stroke are enlarged from the XR600R specification. Despite a 3 millimeter increase in diameter, the XR650's three-ring piston is 10.6 grams lighter than an XR600 slug. An automatic XR400R-type adjuster makes sure there's never slack in the cam chain. A new closed-deck head construction creates a significantly stiffer cylinder and an improved head gasket seal, shaving 230 grams, by using four cylinder studs instead of the XR600's six. Cast from a new corrosion-resistant alloy that is 10 times stronger than previous alloys, a new CR-style magnesium cover provides easy access to the XR clutch.

The newest XR's bottom end is tougher and more efficient. A gear-driven counterbalancer squelches the big single's endemic shaking and drives the engine's water pump from the right end of its shaft. Like the previous XR, the 650 engine is dry-sump, carrying its engine oil inside the frame in a space at the juncture of the cast-aluminum steering head and extruded-aluminum main downtube.

Strategically placed partitions in the crankcases minimize power-robbing windage by keeping excess engine oil away from the crankshaft. Ignition componentry runs dry, rather than in an oil bath, as in the XR600 engine for the same reason. Also, the crankshaft cavity features a Honda first: a one-way reed valve that allows piston pressure to force excess oil into the transmission area.

Working with Honda's cam-actuated automatic decompression system, a new reduction ratio in the kick start gear makes lighting the big XR's fire easier, by spinning the engine faster with each stroke of the kick lever