2005 Honda CRF450X Technology

1/19/2005 3:15:37 PM

Imagine if you will, a family with twin brothers. These brothers, however, are fraternal twins, not identical twins. Although bonded to each other with inseparable genetic ties, they are still and all quite unique from one another. Let's also suppose these brothers are both excellent athletes, uniquely gifted. However, one eventually chooses to pursue the sport of football, while the other takes up basketball. And while these two sports are entirely different, each of these two brothers excels in his own chosen venue, and the twins quickly emerge as superstars.

This analogy perfectly describes the kind of relationship shared between the Honda CRF450R motocrosser and the brand-new CRF450X off-road warrior. Both have been spawned by the creative minds at Honda, and both can be considered twins with regard to the mechanical genomes that comprise the powerplant and chassis wielded by both machines.

However, even though the CRF450X faithfully follows the R-model's basic engine and chassis architecture, virtually every piece has been re-engineered to fulfill a completely different mission: To be the best open-class off-road machine in the world.

A winner by design

Like the CRF450R, the roots of the 450X engine spring from a high-tech, liquid-cooled four-stroke layout with a bore and stroke of 96mm x 62.1mm, to yield a displacement of 449cc. But the design element that sets both bikes apart from any other four-stroke is Honda's innovative Unicam™ single-overhead-camshaft configuration with a separate cam holder that contributes to a notably compact design.

This design incorporates a carburized single camshaft that directly actuates two titanium intake valves. The camshaft's single exhaust lobe acutuates two steel exhaust valves via an innovative forked rocker arm that incorporates a small roller bearing. This roller bearing significantly reduces friction, and therefore wear, so the cam lobe can be narrower and lighter than traditional counterparts. Valve adjustment is accomplished with shims; the intake valves use a direct shim-under-bucket system, while the two exhausts incorporate shims between the rocker arms and keepers on the valve stems.

Because this big-bore engine already churns out power to spare, Honda engineers enjoyed the luxury of reshaping the copious power curve so the CRF450X would deliver what off-road riders prize most: a responsive, torque-laden engine that puts easily accessible power to the ground under all conditions. Therefore, the X-model incorporates a new camshaft that enhances the torque spread compared to the 450R, with new timing specs as follows, reflecting less duration and overlap:

Intake valve: CRF450R CRF450X
opens 15 BTDC 10 BTDC
closes 50 ABDC 45 ABDC
.
Exhaust valve: CRF450R CRF450X
opens 55 BBDC 50 BBDC
closes 15 ATDC 15 ATDC

The CRF450X also sports a brand-new cylinder head fitted with ultra-lightweight titanium intake valves with faces measuring 1.0mm smaller in diameter (35mm vs. 36mm). The steel exhaust valves are likewise a pinch smaller (30mm vs. 31mm), and they have been crafted out of an especially durable and heat-resistant steel alloy. These changes, along with alterations to the 450X intake tract, increase the velocity of the incoming air/fuel mixture, thereby enhancing low-end and midrange torque production and throttle response.

Both machines boast a slipper-type double-ring forged piston for a high 12.0:1 compression ratio. Even though the piston measures a whopping 96mm in diameter, it's endowed with an ultra-short skirt - enough so that it resembles a piston crown that's sprouted wrist-pin bosses. As a result, this big-bore single-cylinder engine can reach a rev ceiling off-road riders could only dream about before the advent of Honda's CRF technology. Both 450s also feature a new piston ring groove in 2005 that cuts down on oil consumption - yet another important step in the ongoing refinement process. And taking a page from the design book on Honda's CRF250 series, the 450X incorporates an oil jet that sprays a steady stream of engine oil up to the underside of the piston for an extra measure of engine cooling.

Like all 450 and 250 CRFs, the 450X piston strokes through a durable, low-friction Nikasil® cylinder liner, which enhances cooling and reduces weight since it eliminates the need for a separate cylinder liner. The 450's top end incorporates a connecting rod double-carburized for extra toughness, and it utilizes a needle bearing in the big end to maximize high-rpm performance while also enhancing durability.

The low-carbon steel crankshaft features carburized main journals for maximum durability under high engine speeds, and to make the 450 engine tougher than ever, the X-model sports a stronger big-end bearing plus tougher main bearings, and newly added thrust washers surround the crank big-end for extra longevity. Another high-tech carryover, the gear-driven counterbalancer system does double duty by quelling vibration and driving the water pump-again - another testimony to Honda's efficiency in design.

A Keihin 40mm flat-slide carburetor, basically the same unit mounted on the 450 motocrosser, feeds the 450X engine. Large amounts of engine vacuum typically make the flat slide in such carburetors difficult to actuate, so the Keihin versions incorporate four small rollers to reduce throttle pull resistance - a very trick touch. In addition, in keeping with R-model precedent, an accelerator pump and a Throttle Position Sensor (TPS) further enhance accurate fuel metering. On the exit side, a longer exhaust pipe is used (688mm versus 662mm for the 450R), one that is also smaller in internal diameter (38.1mm versus 41mm); both changes enhance torque production and low-end/midrange response. Despite this increase in length the 450X muffler is located farther forward than the unit on the CRF450R, closer to the bike's center of mass, thanks to a more pronounced bend in the header section. The muffler incorporates a USFS-qualified spark arrestor and amazingly enough, in standard form the CRF450X meets current EPA noise limits and CARB exhaust emissions requirements.

Off to a great start

Whether you're a family-type weekend recreational rider or a hard-core off-road racer, you'll surely appreciate the cutting-edge, high-tech electric starter system, complete with a sealed, maintenance-free battery and charging system Honda added to the CRF450X. As testimony to the breakneck pace of technological development these days, the electric starter on the 450X is both smaller in diameter (51mm vs. 62mm) and six ounces lighter than the starter mounted on the 2004 CRF250X - despite being used on a much larger engine. Honda accomplished this feat by using neodymium magnets, also known as rare earth magnets, which are currently the strongest permanent magnets available - and magnitudes more powerful than the more common ferrite magnets used in conventional starter motors. Old-school types need not worry; a kickstart mechanism is still retained for backup purposes. To make manual starting easy, the R-model's hot-start lever has been carried over to the CRF450X and it also features a lightweight, compact internal automatic decompressor system to simplify the starting drill when the occasion arises.

Like the CRF450R, the 450X features vertically split crankcases, and while a host of major design features have been carried over, a number of changes make these cases unique to the new bike. The addition of an electric starter increases engine width a touch (0.66 inch), but any change in the rider interface is barely noticeable thanks to a new clutch pack. This new unit features a thinner clutch pressure plate, which shaves the overall width, so the magnesium clutch cover can be kept as narrow as possible.

In keeping with the newest CRF engine designs, the 450X incorporates a twin-sump lubrication system that separates the engine oil from the oil bathing the clutch and the new wide-ratio five-speed transmission. This dual-supply system ensures a cooler environment for the clutch, while also isolating the engine from any potential contamination caused by clutch and transmission material. Because the total volume of oil circulating to the crankshaft, piston and valve train has been reduced, the oil pump supplying these vital parts can be made commensurately smaller and lighter. Separating these systems also allows the use of a smaller oil pan for reduced weight and less power-robbing oil drag around the crankshaft. In addition, the oil bath surrounding the eight-disc clutch will be subjected to a lower heat load.

Sharp-eyed observers will also note the absence of an oil-level view window in the side case. To power its electric starter and lighting system, the CRF450X incorporates a larger AC generator, which would have obscured a sight window; hence the addition of a dipstick for the 450X. This generator, by the way, also features lightweight and compact neodymium magnets to produce 48 watts max output.

A new wide-ratio five-speed gearbox makes the X-model more adaptable to the huge variety of riding conditions encountered off-road. Final drive gearing is also lower thanks to a 51-tooth rear sprocket that replaces the R-model's 48-tooth sprocket; both bikes use a 13-tooth countershaft sprocket. First gear in the CRF450X is lower (numerically higher) than with the CRF450R, and the X gearbox also tops out with a taller fifth gear:

. CRF450X CRF450R
1st gear: 2.230 (29/13) 1.800 (27/15)
2nd gear: 1.625 (26/16) 1.470 (25/17)
3rd gear: 1.235 (21/17) 1.235 (21/17)
4th gear: 1.000 (19/19) 1.050 (21/20)
5th gear: 0.826 (19/23) 0.909 (20/22)

The primary reduction gears remain the same (2.739, 63/23), but to deal with the jarring obstacles encountered off-road, the CRF450X transmission gears are physically wider and beefier than the R-model gears.

In keeping with the off-road mission of the 450X, the rear wheel is an18-incher to better resist tire punctures. Like the CRF250X, the 450X features the new-style T-ring sealed drive chain, which is narrower, lighter and stronger than conventional O-ring chains.

All the same, but all new

Going strictly by the book, the CRF450X features a fourth-generation Honda aluminum frame - the same designation applied to the CRF450R and both CRF250s. But perhaps a more accurate description of this frame might be a fourth generation, Mark II frame: It incorporates the same overall design as the 450 motocrosser, but has been reengineered and tuned specially for off-road use. In short, few pieces carry over between the frames of the two 450s - the X version is that different.

Why would Honda go through the considerable trouble and expense of building a completely new frame? Simple: off-road events take place in an entirely different world than motocross races, one that demands radically different performance parameters. As Honda's development engineers embarked upon this transformational process, they attacked the toughest off-road areas across America to develop specific frame alterations. And slowly but surely, a new, off-road-specific chassis began to emerge.

Such real-world hands-on adjustments could be applied to the Honda chassis because of its superior basic frame design. Technically speaking, aluminum has a lower specific gravity compared to steel, so there is a much greater latitude of adjustments that can be made compared to working with steel frames. For the 450X, Honda engineers charged full-speed-ahead into an incredibly involved development process.

As a result, the array and degree of alterations made to the CRF450X frame are plentiful. The lower frame rails changed, with .05mm thicker walls than the R cradle. The steering head casting is new. The front frame joint is different. New side pivot plates bolt up on the left and the right sides. Even the frame gussets have changed in shape and size. Such alterations modify the stiffness of the frame members and overall chassis in huge ways; for example, making them resistant to up-and-down flex, while still allowing side-to-side resilience, both in precise increments.

The list of changes goes on and on, with every alteration aimed at crafting a new frame with an entirely different personality, one that yields greater bump absorption over the broad spectrum of obstacles typically encountered off-road. In the end, Honda's engineers accomplished the mission they had targeted for the CRF450X: to create a cutting-edge off-road frame with the same kind of handling confidence found on the CRF450R motocross machine.

The best of the best

Of course, creating a world-class motorcycle chassis entails more than fabricating a superlative frame. All of the top-quality chassis components that make the CRF450R such a potent weapon have been carried over to the CRF450X, but again these elements have been retuned and refined specifically for the new task at hand. The lightweight 47mm inverted Showa® twin-chamber cartridge fork is fully adjustable for compression and rebound damping, with 12.4 inches of travel. This new fork features lightweight aluminum damper rods for less unsprung weight, plus new damper specs to soak up the unending processions of obstacles found off-road. The fork springs in the CRF450X are marginally stiffer (0.47 kgf/mm compared to 0.46 kgf/mm) than those used in the R-model motocrosser to compensate for the additional weight of all the X-model's off-road extras. Honda's renowned Pro-Link® suspension system graces the rear end, and while it too delivers 12.4 inches of fully adjustable travel like the CRF450R, a new linkage system yields less rising-rate progression, while less compression damping compared to the R-model also helps deliver a plush ride with more compliant rear-end response.

To provide state-of-the-art braking action, the CRF450X boasts large, motocross-style 240mm disc brakes mounted at both ends, with a dual-piston caliper up front. Like the CRF450R, the X-model also incorporates a first-class aluminum swingarm constructed with a dual-axis, double-taper design, plus a stout cast aluminum crossmember for rigidity. Practiced eyes will spy the X-bike's new box-section subframe, which has been strengthened to handle the weight of the de rigueur spark arrestor while also providing more convenient mounting points for affixing the battery and other electrics. As another nice touch, HRC works-type lightweight aluminum spoke nipples help reduce unsprung weight in the wheels.

Other nice touches include a new impeller for the cooling system that runs at reduced pressure for increased durability, larger radiators that provide a 9.4 percent increase in cooling capacity - with a catch-tank located behind the front skid plate for extra protection - and a larger 2.27-gallon fuel tank (the 450 motocrosser holds 1.9 gallons) that should yield a range of more than 50 miles per tank under most conditions. The 450X also features a new seat that's wider and has more rounded edges for improved rider comfort, and it's made with multiple-density foam to keep you smiling during those day-long forays.

As would be expected, the off-road 450X features a sidestand, but take a close look because this is one trick item: the mounting point for the sidestand has been integrated into the rear portion of the left foot peg bracket. Therefore, the sidestand can be quickly removed if desired, or eliminated completely for racing by swapping out the foot peg bracket with one made for the CRF450R.

Motocross-inspired touches a la Team Honda include the durable Renthal handlebar, quick-adjust clutch perch for easy on-the-fly adjustments, and aggressive-looking racer-style plastic bodywork that includes new venting on the right side panel to provide escape hatches for heat from the exhaust pipe. Then there's the trick non-slip seat cover, plus the new quick-access airbox, svelte headlight and slim-line LED taillight and so much more.

With the X model added to the line-up, Honda now offers fraternal twin big-bore four-stroke machines, each outstanding in its own field. The real question here is: Which game do you want to play, motocross or off-road riding? If it's the adventure of off-road riding that lights your fire, the CRF450X will certainly become your favorite son.