Above: Valentino Rossi and the 2004 MotoGP Yamaha YZR-M1

Yamaha YZR-M1

2004 MotoGP machine
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3/2004 -After a respectable debut for the YZR-M1 in the inaugural MotoGP World Championship during which Yamaha finished second overall with two race wins, 2003 would prove to be less accommodating. After only one podium result the M1's highest overall placing last season was seventh. As a result Yamaha reviewed the situation with the intention of implementing any improvements during the 2004 pre-season. Under the guidance of 52-year-old Masao Furusawa - General Manager of Yamaha's Technology Development Division - a man with a reputation for solving the most difficult issues, Yamaha has come back with a fresh perspective.

Above and below: Carlos Checa's factory Yamaha YZR-M1 sponsored by Fortuna.

As preparations were being made for the 2004 pre-season headlines around the glob were plastered with the announcement of Valentino Rossi joining Yamaha for its assault on the 2004 MotoGP title. For Yamaha it's the icing on the cake and by the time the multiple world champion first sampled the M1 there was plenty to satisfy his pallet. "We had prepared different specification engines and chassis and many smaller items," explains Furusawa. "We started with four types of engines and four types of chassis to try. I had already decided for myself which combination I thought would be the best choice for our new bike, but I kept this to myself and waited to see what Valentino's thoughts were. I'm very happy to say that we think alike."

As a result the YZR-M1 will continue with its in-line four-cylinder engine layout, but with a revised firing order to improve predictability and drivability. In addition to increasing rider confidence the more linear power delivery will prove to be most beneficial during the latter stages of the race when tyre wear often come into play. With 240-plus horsepower control and confidence are very influential.

"Taking all this into consideration I still feel that the inline-four engine configuration offers the biggest advantages… it just needed a little fine-tuning," continues Furusawa. "This engine layout is by far the most compact, from front to rear, allowing us to concentrate the bike's mass where we need it. The inline-four also has less moving parts - a V-four for example has more camshafts than an inline-four - and as a result less friction. And with the forward biased cylinders the dynamic weight distribution can help improve front-end traction.

"It was clear, however, we needed to improve the way the power was delivered, and how that was transmitted through the rear tyre," continues Furusawa. "And I'm confident this latest generation of the inline-four has done just that."
Yamaha's simple yet innovative adjustable engine braking system remains for 2004. To ensure stability during heavy braking Yamaha experimented with a number of concepts before settling on a simple yet effective engine braking system for the YZR-M1, known as an Idle Control System (ICS). Basically the system works in conjunction with the throttle twist grip, which controls the opening of the four throttle bodies. Two of these throttle bodies, however, are influenced by the ICS which adjusts the throttle opening based on the input of the M1's ECU during deceleration. The input of the ICS can be adjusted to suit the rider's preference.

In addition to the refined engine performance Yamaha also considered where the Deltabox chassis could be improved. Although the M1 was by far the lightest in handling and the most nimble in character it was gaining a reputation as being rather flighty in nature. This became evident at bumpy circuits, which could easily unsettle the M1. To improve the bike in this area chassis flex was put under the microscope with the following outcome.

The first of the 2004 prototype chassis', which included a new inverted rear swingarm, was sampled by Checa at the Valencia MotoGP late last year. Although the torsion rigidity remained pretty much unchanged from the unit before it the lateral rigidity was reduced significantly to improve rider feedback at high lean angles. In addition this has also made the bike more forgiving over less than ideal terrain, making the M1 more versatile. While the inverted rear swingarm, also boasting more lateral flexibility, offers a lower centre of gravity. This in turn makes the bike easier to change direction on.

Furusawa goes on to say: "My main concern during the final stages of last year and during pre-season has been to improve the way the M1 powers off the turns. My aim was to find a base chassis and engine package that would be predictable at every circuit, not just a select few. A foundation that would work even if the rider was unable to find the ideal chassis set-up in the time allowed during a race weekend. I'm pleased to see that Rossi's approach is the same."

That straighter load path makes the Deltabox V frame massively strong, even as it makes the bike narrow to better fit the rider. Together with its light, strong and long Controlled Fill die cast truss swingarm, all that power is deployed to the pavement with the help of a fully adjustable piggyback shock absorber.

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2004 YZR-M1 Specifications
Engine type:
Liquid-cooled, in-line, 4-cylinder, 4-stroke with 20-valve DOHC
Displacement: 990cc
Ignition: Yamaha CDI with adjustable mapping - NGK spark plugs
Carburation: Fuel injection
Lubrication system:
Wet sump - Motul Oils
Data recording: 2D
Maximum power:
More than 240ps
Maximum speed:
Over 320 km/h
Transmission Type: 6-speed cassette-type gearbox, with alternative gear ratios available
Primary drive: Gear
Clutch: Dry multi-plate slipper clutch
Final drive: Chain - DID

Frame type: Twin-spar aluminium frame, multi-adjustable steering geometry, wheelbase, ride height, with aluminium swingarm
Front suspension: Fully-adjustable Öhlins inverted telescopic forks
Rear suspension: Braced aluminium swingarm with single Öhlins shock and rising-rate linkage
Front/rear wheels: Marchesini 17.0 inch front, 16.5 inch rear, available in a variety of rim widths
Front/rear tyres:
Michelin, 17.0 inch front, 16.5 inch rear, available as slick, intermediate, wet and hand-cut tyres
Front brake: Twin 320mm carbon discs with radial mounted four-piston Brembo calipers
Rear Brake: Single 220mm ventilated stainless steel disc with twin-piston Brembo caliper
Weight: 145kg, in accordance with FIM regulations
Fuel capacity: litres, in accordance with FIM regulations