Cycle News - Archive Issues - 2000's

enlarge the bore, since they're so happy with their current combustionchamber arrangement). Hence, poundage was shaved off the valves, piston, flywheel, crankshaft, etc. Oh, and following the lead of the race team, one gear - fifth - was eliminated from the transmission, while the other four ratios were raised slightly to match the increase in power (says Butler: "In the beginning, we used five speeds [on the race bike], but we were never using fifth. Now Ferry uses four for outdoors, and in supercross, we use a three-speed"). The third target - light handling presented a formidable challenge, since a four-stroke's inherent larger engine size limits chassis arrangements (on a two-stroke, the smaller mill can be placed pretty much anywhere, a fact that greatly increases the likelihood of achieving optimal handling). Yamaha, in particular, faced a chore here, since it prefers the precise valve control allowed by a dual-overhead cam design (Honda and KTM have both opted for the less sizeable single-overhead cam arrangement), but by making their valves smaller and more vertical, Yamaha was able to move them close together and save some space here. The cases are also smaller (although the crank- shaft, counterbalancer shaft and f:S[j)@@5(J!J@&J715@fJD08 clutch shaft are spread slightly to allow larger gears to withstand the 2001 Yamaha VZ450F increase in torque), and the entire engine is so much smaller that it can ENGINE: Uquid-cooled, forward-inclined single-cylinder, five-valve (titanium), DOHC DISPLACEMENT: 449cc BORE x STROKE: 95.0 x 63.4mm COMPRESSION RATIO: 12.5:1 STARTING SYSTEM: ...............••..••.•.•..•...•..•.............Kick LUBRICATION SYSTEM: _ Dry sump TOTAL OIL CAPACITY: _ 1.27 qt (1.2 L) COOLANT CAPACITY: 1.27 qt (1.2 L) FUEL CAPACITY: .......••••.....•••••.•••••••••........... 1.85 gal. (7.0 L) AIR ALTER: Wet-type foam element OVERALL LENGTH: ...••••...............................85.5 in. (2171mm) CARBURETOR: 39mm Keihin FCR flat-slide w/throttle-position sensor SPARK PLUG: . _ NGK CR8E (resistance type) IGNITION: .......••••••••...................................CDI magneto CLUTCH TYPE: ...................••....•.•••............Wet, multiple-disc GEAR RATIO: ..................•••••••••••.•......••..........1st - 1.929 2nd - 1.563 3rd - 1.278 4th - 1.050 FINAL DRIVE: ........••••••••..•...............................520 chain FRAME: Semi-double cradle RAKE/TRAIL: .....••••••••..................................27.2°/118mm FRONT WHEEL: _ Excel rim w/ lightweight hub, aluminum nipples and 80/1 00x2 I 51 M Dunlop 739 tire REAR TIRE: .Excel rim w/ lightweight hub, aluminum nipples and 11 0/90x 19 62M Dunlop 739 tire FRONT BRAKE: Single 250mm floating disc (hydraulic) REAR BRAKE: .single 245mm disc (hydraulic) FRONT SUSPENSION: Telescopic Kayaba fork w/ 11.8 in. (300mm) travel REAR SUSPENSION: Swingarm, link-type w/ Kayaba shock and 12.4 in. (315mm) travel OVERALL WIDTH: .32.6 in. (827mm) OVERALL HEIGHT: .51.3 in. (1303mm) SEAT HEIGHT: ...................••......................39.2 in. (995mm) WHEELBASE: 58.8 in. (1485mm) GROUND CLEARANCE: 14.6 in. (371mm) CLAIMED DRY WEIGHT: 222 Ibs. (100 kg) SUGGESTED RETAIL PRICE: ...............•.•••.•.•..•.............$6299 be mistaken for that of a YZ250F. In addition, Yamaha gave the bike new bodywork that is much flatter and smoother, allowing the rider to more easily change position on the bike very important for handling. Although it resisted Honda's and KTM's cam arrangement, Yamaha did follow those companies' lead when it came to achieving its final goal - easy starting. The company finally ditched its awkward and complicated manual compression-release lever for an automatic system. In addition, the hot-start mechanism is now actuated via a handlebar-mounted lever, so the rider isn't forced to reach down to the carburetor when he stalls during a moto. If the aforementioned on-paper achievements don't validate a sense of pride, we don't know what does unless it might be a corresponding improvement in seat-of-the-pants performance. Did Yamaha attain that as well? To learn, read tester Chris Sprenkel's evaluation in this story's "From the Hip" sidebar. eN Hayashi: "The four-stroke benefits. APorter:both." can't make onehas benefits, but the two-stroke also has still go thisWe want to keep "You bike that covers both categories. We'll way [with Needless to say, there are a lot of people involved in the creation of an all-new motorcycle especially when that motorcycle comes from a manufacturer the size of Yamaha - but two of the most influential individuals involved on Yamaha's new YZ450F are Yasuo Hayashi (the YZ project leader, who works out of Japan) and Mark Porter (Yamaha's head engineer in the U.S.). Both have been at the company for quite a while (Hayashi, perhaps not coincidentally, was put in charge around the time Yamaha started dominating the magazine shootouts, and Porter tells stories of working with roadrace-tuning legend Kel Carruthers). At the press introduction in Lake Whitney, Texas, we chatted with the duo about its new pride and joy. When did Yamaha first make the decision to completely redo its big·bore MX fourstroke? Hayashi: "It was 2000. When we went from a 400 to a 426, the handling started to get heavy, so we tried using a smaller engine to get lightweight handling - a 400. Of course, we didn't have the power, so then, we decided to match in light handling with a big engine. That's why you see a lighter flywheel mass and all those things." Porter: "The target was getting the biggest engine with the lightest handling." Hayashi: "We limited it to 450, because that's the FIM's new displacement limit [for the 250cc class]. Four-strokes will compete with two-strokes, and the maximum displacement is 450cc. Displacement is a very important item, and we got a lot of information from our GP racing division_ The displacement of Stefan Everts' bike was very high - I think 500cc - so we chose the maximum." Porter: "There's two or three years of studying that happens before we make the final decision. We build and test and build and test, and then we make a decision based on a couple of years of study." Q A QSo the final decision was made before you knew anything about Honda's CRF450R? A Hayashi: "Yes, Honda was no influence." Q What about after the Honda came out? The fact that your claimed weight is one pound less than the Honda's can't be a coincidence. Hayashi: "Honda's direction and Yamaha's direction are different. I think. Honda's direc- A tion is more like enduro ~ it's a mellower engine. Yamaha is more aggressive. It Porter: "It's an interesting question. Yamaha doesn't follow anybody. If you follow, you're always behind - you never catch up. So we take a different way, and we think our way is the best way for a motocross rider. We think Honda's direction is more of a desert bike or a playbike. The weight was a surprise to us. We didn't think we'd achieve that light weight because we think Hondas aren't durable - we thought, 'Oh, no, we're never going to do that with Yamaha durability standards.' When it came over lighter than the Honda, we were pleasantly surprised. That was nice to beat their weight, but we just wanted to make the lightest possible four-stroke motocrosser while keeping Yamaha durability." Q What were your goals, then? Hayashi: "We targeted our two-stroke - the YZ250 - for weight and handling. The average rider was very satisfied with the 426, but the pro-level guy was not, because It was too heavy. What we wanted to do with the 450 was satisfy the average guy and the top-level guy. In AMA motocross and supercross, the top riders were choosing YZ two-strokes, so that was A our competition." Q Speaking of the two-stroke, what is its future? both two- and four-strokes] as long as the market will let us. The [emissions] regulations don't cover dosed-course use at this time, so it's still good to have two categories. They don't ever cover closed-course. In '05 and '06, they will start affecting off-road, but that's different. Closed-course has an exemption." Hayashi: "Now, in supercross, there are very few four-strokes. I'd like to see about 50-50 Yamaha two-strokes and four-strokes." Q What was the general process, from decision to finished product? Porter: "Japan has the decision, but the United States has the largest on A what happens, because finalYamaha, YZ sales in thewith the Unitedbiggest. andinfluenceFor for U.S_ are the We influence it more than other markets. So it's back-and-forth testing States Japan. example, we had a 426, and they sent us a different engine· old chassis, new engine. And then we tested a 426 in a new chassis. Then it comes together as a prototype, and we do testing. They make changes, and then we do testing again, so it's a fairly long process. The engineering and the details are all done in Japan, but we have the freedom to modify some things in the U.S., and then ask them to approve them or test them in Japan. "The difficult part, I guess, is Japan test riders are different from U.S. test riders. They ride the same tracks every day, and they know every bump on every track. In the U.S., we go to a variety of different tracks, and our riders are somewhat more aggressive. It's good to have both. We have to have an understanding on both sides, so we can move forward. Hayashi has been very good at putting those two influences together. That's why, since about '96, Yamaha has been pretty high up there. Yamaha Japan started listening to Yamaha U.S. riders' opinions, and once everyone started understanding what we wanted, then we started making leaps and bounds." lt seems that Yamaha made a conscious decision to go pure-motocross with the YZ450F - it has fewer gears and less fuel capacity. Porter: "We could have kept the five-speed and tried to make the model fit for off-road, but we felt we would have sacrificed YZ function. So we broke off and went all-YZ. Our WRs, you notice, now have electric start, so they fit that market better, and the YZ fits this market better. Instead of trying to make one model do it all, we can focus more. To get more competitive - get the lighter weight while getting the durability that we need for motocross - you need to go that way." Q A Relative to two-stroke Q motocrossers, fourstroke motocrossers are still young. Can four-stroke technology stilI be Improved greatly? Porter: "Two-strokes have hit the level where they don't change a lot; four-strokes are still on the growth curve. Lightweight materials are a big area, and power delivery, chassis rigidity - things like that." Hayashi: [Points at head and smiles] "I have many ideas for the future." A cue •• n _ _ S • SEPTEMBER 11, 2002 45

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