When somebody mentions a spring, you probably picture a standard coil spring that looks like a steel pigtail. Most motocrossers immediately envision the shock spring on a race bike. A spring, however, is any elastic object that stores energy.
A lesser known type of spring is a Belleville washer. Belleville washers are a type of disc-shaped cup with an extremely high tensile strength. Originally developed in the mid-19th century by Julian Belleville, Belleville springs are used in a variety of environments where a heavy load bearing ability is required. Belleville springs can be made in a wide range of sizes (from very small washers to very large discs). Their shape resembles a shallow soup bowl with the bottom cut out, and they are generally made from tempered steel to stand up to immense pressure. Because of their construction, Belleville springs distribute weight evenly around their circumference. As a result, they can be used to hold substantial loads and are highly useful in areas subject to thermal expansion, vibration and high bolt loads?all of which describe a motorcycle clutch. The Belleville washer clutch spring is a creative idea (although old hands will remember that Maico used Belleville washers in their clutches decades ago).
Hinson recognized certain advantages of the Belleville design over the traditional coil spring-equipped clutch, and they have actually been using this type of spring in their slipper clutches for about four years. The Belleville washer distributes the load around the radius of the pressure plate (as opposed multiple individual springs arranged in a circle). Additionally, traditional coil springs tend to bow out or bend over to the side when compressed. This flexing results in friction (rubbing) against the sides of the pressure plate as the clutch disengages.
The German-made Xtrig triple clamps offer adjustable offset and vibration-isolating handlebar mounts.
It was Roger DeCoster who first registered complaints about the rubbing issue, and the concerns of “The Man” were enough of a catalyst for Hinson to continue development on their Single Spring (SS) Belleville washer clutch. Much of Hinson’s early development and durability testing was done on quads, which have very similar engines, but are under increased loads because of their extra weight and bigger tire footprints. Currently, Hinson has pro riders running the all-new SS (Single Spring) clutch for durability testing.
MXA first saw the Hinson SS clutch about a year ago, and we were curious to see how it worked. Hinson agreed to build us not just an SS clutch, but a complete project bike as a test unit. They could have just given us the clutch, but they wanted to build a test bike that used a mid-level AMA pro as the target rider. We commend Hinson for going for the gusto and building a bike to challenge their new clutch. We definitely hammered their bike (and the SS clutch) over our test period. Here are the results.
SHOP TALK: BENCH WRENCHING
Hinson started with a fresh 2009 Honda CRF450 from John Burr Cycles in SoCal and went to work. Running a Hinson SS clutch only requires a new Hinson inner hub and pressure plate. The price tag for these two parts is around $600. Naturally, our test bike was also outfitted with a Hinson basket, clutch cover and clutch plates?which doubled the cost. Hinson stresses the importance of running the stock clutch perch, because some aftermarket perches have different leverage ratios that can cause the clutch to slip.
Yoshimura not only supplied the exhaust system, but the cam, ignition and transmission coating.
The QTM oversize front brake system is just what the doctor ordered on the Yosh-powered CRF450.
As for the engine, Hinson claims they didn’t go all out on it, but we disagree. Yoshimura massaged the CRF450 engine with a titanium RS4 exhaust, Yosh camshaft, Rem transmission service, PIM 2 program and Data Box ignition (which utilizes a sensor in the head pipe to read air/fuel ratios to help make fuel-mapping changes). Additionally, Hinson added a Faction intake valve kit in an effort to get the most out of the Yosh camshaft. The kit included stainless intake valves, high-rev valve springs and Ti retainers.
The piston was a 13.5:1 CP that was powered by Ti Lube TF-4U AMA-legal fuel ($75.00 for 5 gallons). Yosh told us that with the fuel-mapping capabilities of the PIM 2 we could also get away with 91-octane pump gas. Finally, the bike utilized a Twin Air Power Flow kit and Maxima oils and lubricants. Hinson laced up Excel A60 rims, Dunlop MX51 GeoMax tires and a 270mm QTM front rotor kit.
As for the suspension, Hinson went to little-known C4 MX suspenders for a tune-up. They went stiffer on the shock’s high- and low-speed compression and made the fork’s TCV valves smaller, which effectively makes the forks ride higher in their stroke. C4 went to the next stiffest spring rate in the forks and kept the stock shock spring. C4’s basic fork/shock package costs $500.00 (plus the cost of springs).
Hinson’s full-race Honda CRF450 is designed for one purpose?to showcase their all-new Belleville washer-controlled SS clutch. They felt that the best way to test a clutch was to build a powerful version of the bike with the worst stock clutch.
Renthal provided TwinWall handlebars, rear sprocket and Kevlar grips. Our project bike also had a LightSpeed carbon fiber skid plate and carbon fork wraps. The chain was by RK, and the graphics were by FLU Designs.
Last, but not least, were the Xtrig triple clamps and shock preload adjuster. Xtrig isn’t well-known in the U.S., but sponsors several factory teams in the GPs. The clamps were standard offset, but could be flipped around to offer a 22mm offset option.
TEST RIDE: HANG ON AND PRAY
MXA‘s test riders have ridden National privateer and factory 450s, and we can easily say the Yoshimura engine was faster than many of those. Hinson’s stated goal was to build a competitive machine for an AMA National privateer, and they succeeded. When we first started testing Hinson’s CRF450, we didn’t know the full extent of the internal engine modifications. Surprisingly, we had a virtually identical Yoshimura engine on one of our race bikes (although it lacked one or two of the Hinson bike’s bells and whistles). The addition of the intake valves, PIM 2, and race fuel definitely pushed the engine up to the next rung of the ladder. The powerband was beefy off the bottom and then jumped like a frightened gazelle in the midrange. The midrange hit was awesome for getting on top of soft terrain and wheelying over obstacles. It should be noted that less talented test riders had to anticipate the powerband to prevent arm fatigue.
To make the powerband more usable (not so aggressive), we played with the Yoshimura PIM 2 and Data Box. The 12.8:1 fuel/air ratio that Yosh and Hinson had installed in the bike was optimized for maximum horsepower. We experimented with 12.5:1, 12.3:1 and 12:1. The consensus was that the 12.3 ratio took away the jolt and made the powerband significantly more usable and forgiving.
Compared to the sloppy, vague feel of the stock four-spring Honda clutch, the Hinson SS clutch was a huge improvement. The friction zone on the SS clutch was very tight and precise.
Originally built for James Stewart’s YZ450F, LightSpeed now makes their one-piece carbon fiber skid plate for the CRF450.
To compare the performance of the SS clutch to the stock clutch, we raced the Hinson bike back-to-back with our test bike (with stiffer springs). Compared to the sloppy, vague feel of the stock four-spring Honda clutch, the Hinson SS clutch was a huge improvement. It should be noted that the release point of Honda’s actuation arm is a real hindrance to getting the CRF450 clutch to work. Eve with the Hinson SS clutch the friction zone on the SS clutch was very tight and precise. When letting the lever out, the clutch had a solid, sudden rngagement point which let riders put power down quickly. The clutch lever actually got easier after the first little bit of travel. Tactile feel is a personal thing, and some MXA test riders liked the firm-to-easy feel of the SS clutch, while others liked the easy-to-firm feel of the stocker. Nobody liked Honda’s small actuation range, but that isn’t Hinson’s fault.
The C4-tuned suspension worked well when ridden aggressively, but not very well at speeds below quasar. That isn’t to say the suspension was too firm, but more that it stayed too high in its stroke. Every test rider thought that the Hinson CRF450 was unbalanced towards the front. Every test rider spun the clickers to suit his tastes and found a usable zone.
You gotta love the oversized QTM brake rotor. It only required a feeble index finger to get strong stopping power. This came in handy on steep downhills and at the end of long straights. Our best technique was to squeeze the front brake lever until the rear wheel came off the ground, then let up slightly.
WHAT DO WE REALLY THINK?
In truth, the MXA wrecking crew was only interested in testing the Hinson SS clutch system?which we think is a solution to a major CRF450 problem (but not a perfect solution). That said, the complete Hinson CRF450 was a purposeful bike that would suit any aspiring National pro. Yes, the suspension could be tuned better for each MXA test rider’s taste. Yes, we thought that the powerband setup was way too aggressive. Yes, we loved the powerful front brake. But the real question hinges on what we thought of the clutch. Our first impression of the SS clutch was that it was a vast improvement over the stock CRF450 four-spring unit. But beating Honda’s spaghetti-like clutch isn’t difficult. The Belleville washer idea has tremendous merit: It is easy to change (one spring instead of four or six); different-shaped cupped discs offer different spring rates; and the spring pressure is equal across the pressure plate. Good stuff.