Iconic motorcycles: the Yamaha YZ400f
In the winter of 1996/1997, Yamaha developed a 4-stroke motocross bike that seriously shook the dominance of the two-stroke dirt bike. The two-strokes took over since the XNUMXs and remained so until the turn of the century. The idea of using a cumbersome and heavy four-stroke seemed crazy and almost unthinkable, but at Yamaha they saw it differently.
In the spring of 1997, Yamaha came up with a revolutionary machine that they used to compete in competitions such as the Motocross World Championship and the AMA Supercross Championship. Andrea Bartolini's factory YZM400F machine won a World Championship 500cc race at the Italian GP in April '97 and in the US a Doug Henry won an AMA Supercross in Las Vegas a month later. These two victories heralded the beginning of a new era of 4-stroke motocross riders.
Yamaha's idea was revolutionary. It mainly consisted of the will to make the four-strokes high-revving. As a result, the driven mass in the engine had to be made as light as possible. The YZ400f proved that you could dramatically change the character of a four-stroke engine by keeping the weight and number of internal parts to a strict minimum. In 1999, Bartolini won the 500cc World Championship with a four-stroke Yamaha. It was the starting signal for the big change in motocross and that is why the YZ400f can rightly be nicknamed “gamechanger”.
Yamaha YZ400f specs (1998)
Engine type Liquid cooled 4-stroke, DOHC, 5-valve
Displacement 399 cc
Bore x stroke 92.0 x 60.1 mm
Compression ratio 12.5 : 1
Lubrication system Dry sump
Fuel System Carburettor (FCR39H)
Clutch type Wet, multiple disc
Ignition system C.D.I.
Starter system Kickstarter
Transmission system Constant mesh, 5 speed
Primary reduction ratio 2.952
Secondary reduction ratio 3.500
Final transmission Chain
Ratios gearbox 1st 1.929
Gearbox ratios 2nd 1.563
Ratios gearbox 3rd 1.278
Ratios gearbox 4th 1.091
Ratios gearbox 5th 0.952
Front suspension system Telescopic fork, USD
Front wheel travel 300mm
Rear suspension system Swingarm (Link suspension)
Rear wheel travel 315mm
Caster angle 27.8°
Trail 123mm
Front brake Single disc, Ø 245 mm
Rear brake Single disc, Ø 220 mm
Front tire 80/100-21 51M
Rear tire 110/90-19 57M
Overall length 2,176mm
Overall width 827 mm
Overall height 1,303mm
Seat height 991mm
Wheelbase 1,495mm
Minimum ground clearance 373 mm
Service weight (incl. liquids) 115 kg
Fuel tank capacity (reserve) 8 L
Engine oil tank capacity 1.7 L
Photos: Yamaha
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