Yamaha pushes four-strokes

The direction of the 2005 Yamaha lineup has definitely gone four-stroke, with four upgraded models and five all-new models with cleaner-burning engines.

Five two-strokes from the 2004 lineup will be available in 2005, but with minimal changes and no marketing emphasis, said Rob Powers, snowmobile marketing manager for Yamaha.

Powers said that Yamaha’s interested in four-stroke development began six years ago in anticipation of EPA regulations, now scheduled to take effect in 2006. The company plan, he said, is to prove that four-stroke snowmobiles have enough power to satisfy the snowmobile customer and to expand the four-stroke engines to all models.

The new models for 2005 are the RS Vector (ER), a trail machine, and the RS Rage, which Powers called “a little brother to the RX Warrior” trail/off-trail snowmobile, the RS Vector Mountain, and the RS Venture 2-Up. These machines use a new, a 120 hp four-stroke engine.

Undergoing significant changes for 2005 are the RX-1, RX-1 ER, RX-1 Mountain, and RX Warrior. These machines have new and upgraded suspensions, as well as other lightweight components.

Returning with minimal change are the SXViper Mountain and VK 540 III. The SXVenom, the SXVenom ER and Venture 600 have only graphic updates.

The RS models use a three-cylinder four-stroke engine Yamaha’s named the Genesis 120. The 973cc engine delivers approximately 120 hp. Powers said the engine is comparable to the 600cc two-stroke class.

The engine is more compact than the Genesis Extreme four-stroke found in the RX-1, and is 22 pounds lighter. It has a double overhead cam with four valves per cylinder.

The engine is a long stroke design, which Powers said offers peak power and torque at lower rpm and, no gear reduction is needed for the clutch. The 40mm constant velocity carburetors are liquid-heated with a throttle position sensor. The engine has a laydown design and is tipped back 37 degrees into the chassis, which is 7 degrees greater of an angle than the engine in the RX-1.


Powers said the Genesis 120 has better acceleration and is easier to clutch than comparable two-strokes. The engine reaches peak is horsepower at 8600 rpm and its torque peak is at 7000 rpm.

Fuel economy with the Genesis 120 was also touted. “The RS Vector has 35% better fuel economy than the SXViper,” Powers said.

“That means you can ride for 200 miles and get a free lunch,” said Mike Amano, Yamaha’s department manager for snowmobile product planning.

Final prices on the machines have not been announced, though Powers said the RS Vector would be priced competitively in its class.

Customer surveys on the Genesis Extreme engine found in the RX-1, RX-1 Mountain and RX Warrior were favorable, Powers said, so there were no major changes to the mill, with the exception of some lighter weight components.

Customers may have responded favorably to the Genesis Extreme engine, but the larger-power four-strokes were given what Yamaha considered an unacceptable rating on comfort and handling, Powers said. “We addressed this some in 2004,” Powers said, “but the biggest need was weight reduction.”

For 2005, the RX-1 weighs 30 pounds less than 2004; the RX-1 ER dropped 23 pounds; the RX-1 Mountain weighs 22 pounds less; and the RX Warrior lost 11 pounds.

Part of the weight loss is due to the incorporation of lighter-weight materials. The non-ER models have magnesium chaincase and valve covers, lightweight gears and a smaller battery. All models now use a titanium exhaust pipe, lightweight rotors, and a smaller brake caliper.

Another significant point for weight reduction was the re-design of the rear suspensions: the new RX-1 suspension is 14 pounds lighter than last year’s.

The RX-1 and RX-1 ER rear suspension use a mono-shock design with multiple adjustment points. It’s called Mono Shock RA, which stands for “remote adjust.”

A dial, located near the drivers left foot, can change the rebound by 30% from its softest to hardest settings.
Preload and weight transfer can also be adjusted. Powers said that more adjustment details will be introduced at fall service schools. The machine comes set up for a 190-pound rider.

The suspension provides better weight transfer, Powers said, which also improved the acceleration.

The RX-1 Mountain also has a new suspension that is a claimed 13 pounds lighter than the 2004 suspension. It’s called the Pro Mountain Rear Suspension, and comes on the RS Vector Mountain, as well. It has a three-position cam spring preload adjuster, adjustable control rods and a 151-inch dual angle rail shape, which angles at 3.5 degrees at the rear.

With the changes, Yamaha claims improved weight transfer, improved deep snow flotation and improved ride comfort.

The RS Vector’s rear suspension is dubbed Pro Active. It accommodates a 121-inch track and gives 11.5 inches of rear travel. It has a three-position cam spring preload adjuster, adjustable control rods, preload adjustors and an “adjustable spring bottoming stopper.” The bottoming stopper, which resembles a spool, can change three positions to adjust bottoming force on the torsion spring. This stopper is meant to work in the bigger bumps.

The new Pro Comfort rear suspension comes on the RS Venture. the 2-Up sled uses a 144-inch track and has a special block torsion spring bottoming stopper, made to adjust between one or two passengers.

The four-stroke machines received some ergonomic perks, starting with a newly designed seat, and handlebars and a windshield that are 25mm taller than last year. The greater distance between the runningboard and the handlebars make for easier standing, Powers said.

Yamaha will have four models dedicated for mountain riding applications, and Powers said the company has put a lot of effort into the RX-1 mountain machine.

Customer satisfaction surveys ranked it low in deep snow performance and overall weight. In addition to the 22-pound weight loss and a new rear suspension, the clutching has been improved.

Ergonomics are similar in the RX-1 Mountain and the RS Vector Mountain. They have a new mountain ski with a stance adjustability of 2 inches. Handlebars are 3.5 inches taller and 2 inches wider, thanks to an aluminum block riser and a straighter bar design. It also has a new, hard grab strap.

The RX-1 Mountain now comes with a rear heat exchanger for improved cooling on groomed trails.

“(The changes on the RX-1 Mountain) opens up the window on who can ride the sled,” Powers said. “The difference between the 2004 to 2005 is huge and it’s easy to notice. It’s so much more versatile. It’s akin to the changes we made from the 1999 to 2000 Mountain Max 700.”

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