Some inventions, tools, and techniques have advanced the sport of motocross significantly since their inception. The Racer X staff explains some of those advancements in this feature, called “Next Level,” and if you’re looking for the biggest change in motocross in the last several decades, you’d be hard pressed to find something more revolutionary than the four-stroke takeover. A machine that was once far behind in the performance category now dominates the racing scene, but it wasn’t always that way. When they were first introduced, they weren’t considered superior machines in the premier class, even with their displacement advantage. There were plenty of innovations that helped them become the refined beasts they are today, and one of the biggest was the adoption of titanium valves.
The use of titanium in racing is nothing new, and there were titanium valves used in race engines long before they were put into production. In fact, Doug Henry’s prototype 400 that he rode back in 1997 had titanium valves! The question is, why are they better? It all boils down to weight. Not in the sense that they make a significant difference in the overall weight of the motorcycle, but when introduced in the 2001 YZ426, they reduced valve weight by 40 percent! This was a big deal because it meant lighter valve springs could be used. In fact, valve spring load was reduced approximately 20 percent, which meant less resistance to the engine. The difference? A snappier, quicker revving engine with more of a free-revving character, less engine braking, and the added bonus of the possibility of a higher rev limit.
The June 2022 Issue of Racer X Illustrated
Original Win/Sin
Twenty-five years ago, Team Yamaha’s Doug Henry became the first rider in AMA Supercross history to win on a four-stroke, marking the beginning of a huge paradigm shift that—for better or worse—still resonates to this day.
A quicker revving engine and a machine with less engine braking were game changers for four-strokes. In those early days, four-strokes didn’t even have close to the snap they do today, which is why most riders still rode two-stroke 250s in supercross. Engine braking was extremely heavy too, like, semi-truck heavy, but thanks to titanium valves, four-strokes took a giant leap forward, which would have otherwise been impossible with mechanically actuated valves, even with the advent of fuel injection later that decade. When we spoke with Yamaha for this piece, it was also pointed out to us that a similar result might have been achieved with pneumatic (air powered) valve activation.
So if titanium valves were clearly better, why weren’t they used earlier? Well, it’s no small thing to simply switch over to a new material in manufacturing. Parts have to be tested for durability, and in this case, mass production required special titanium material and manufacturing techniques. Stuff like that is difficult and doesn’t happen overnight, but fortunately it did eventually happen because that gigantic improvement to the valvetrain helped lead to the motocross rockets we ride today.
Main image by Mitch Kendra
