1997 Yamaha YZM400F

In the mid-1990s, the light weight and explosive power of two-stroke dirt bikes ruled motocross and Supercross. With the exception of a few exotic and low-volume alternatives, four-strokes—which boasted broad power bands—were used for trails and fire roads.

Then came AMA Motorcycle Hall of Famer Doug Henry on a shocking full-factory prototype from Yamaha: the YZM400F. The YZM launched the modern four-stroke revolution and proved that—when AMA displacement rules leveled the playing field—valves and cams could not only compete with reed cages and pre-mix on a Supercross track, they could beat them.

The bike that Henry raced was more than just a different motor. To encourage development of new race-proven technology, in 1997 the AMA started offering manufacturers a one-year exemption from a rule that required teams to start with production motorcycles when building their race bikes.

The reason for the exemption was to spur R&D, and Yamaha took full advantage. The YZM400F featured a hand-built main frame; a carbon-fiber subframe, airbox and engine mounts; magnesium clutch and flywheel housings; a hand-built aluminum gas tank; and a titanium exhaust.

In its first race, at the AMA National Motocross opener in Gainesville, Fla., Henry rode the YZM to eighth overall, following that with a fourth and a sixth in the next two rounds.

The biggest race of this bike’s maiden run, and one of the most memorable of Henry’s career, came indoors, at the Las Vegas finale of the 1997 AMA Supercross Championship. Henry, who raced a YZ250 two-stroke in the early Supercross rounds before he was temporarily sidelined by a minor injury, fielded the YZM400F and won.

Henry’s win cemented a new possibility in the public consciousness: that a four-stroke could beat two-strokes on their own turf. Within a few years, spurred by manufacturers’ rapid development, four-strokes dominated professional motocross and Supercross competition. And it all started with Henry and the YZM.

This exotic YZM is now owned by Henry and on loan to the AMA Motorcycle Hall of Fame in Pickerington, Ohio, where fans of the sport can see it first hand.