Forty-Plus Years of Four-Strokes

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Think the new CRF™450R and CRF250R are starting a four-stroke revolution? Wrong-Honda® fired the first shot more than four decades ago.

It's easy to think Honda's new CRF motocrossers are the first really successful four-stroke dirt bikes. But you couldn't be more wrong. Because, with only a short look back, you'll discover a whole string of revolutionary and successful Honda four-strokes-so many that the two-stroke Elsinore™ and its CR® progeny might seem just an anomaly in Honda's history of four-stroke dominance.

One could start with the Super Cub® back in 1959, a bike countless thousands of baby boomers used as their first dirt bike. But set that aside, and look toward one of the most significant off-road motorcycle feats of the post-war generation: Dave Ekins' and Bill Robertson's first ride through Baja in 1962 on a pair of Honda CL72 Scrambler 250s. These were high-pipe four-stroke twins that, to today's eyes, look far more like street bikes than state-of-the-art dirt machines. But state-of-the-art is exactly what they were at the time. Ekins and Robertson set off to do the unimaginable--no one else believed motorcycle could possibly travel the length of Baja to La Paz nonstop without suffering numerous breakdowns. But that's exactly what they did, due in large part to their bikes' superior four-stroke engine design.

By showing what a virtually stock Honda could do-and even by the standards of the day those two CL72s were painfully stock-Ekins and Robertson and the CL72s paved the way for the annual Baja 500 and 1000 races we have grown accustomed to, just as we have grown accustomed to a Honda XR™ winning the overall every year, handily besting the monster trucks, one-off race buggies, and every two-stroke in the field.

Honda adapted the CL72 from a street bike, the 1961 CB72 Hawk® 250. And by 1969 Honda was ready to introduce its next-generation dirt bike, a machine in which street bike and dirt bike again shared the overall engine design: the SOHC 350 twins. The resulting dirt bike, the SL350, was the motorcycle that really opened up Baja. Custom shops in Southern California latched on to them and produced machines that flat-out blew off the heavy desert sleds that had dominated the desert racing scene. If anything the 350s were better, faster, and more reliable than the CL72s had been.

But the best was yet to come. In 1972 Honda unveiled the most radical concept yet: the XL250 Motosport 250, the first of the long XR and XL lines. Here at last was a motorcycle still recognized as the defining formula for four-stroke off-road bikes, one that's lasted for more than 30 years: a lightweight single-cylinder engine with a single overhead camshaft, upswept exhaust system, high fenders, long travel (for the era!) suspension, and capable off-road handling. Yes, those original XL-series machines were street-legal. But unlike the machines before them the XLs had been designed as dirt bikes first, then simply equipped with the necessities to make them civil road bikes, not the other way around. Just as important, they were as tough as a Baja steak.

Honda's four-stroke XR and XL dominance continues to this day. Along the way the XRs got revolutionary Radial Four-Valve Combustion chamber (RFVC) heads, tons more ground clearance, and single-shock rear suspensions. In 2000 they also broke new ground by debuting the first liquid-cooled four-stroke XR engine, one wrapped in an aluminum frame to create the XR650R. This latest incarnation of Honda's four-stroke off-road line is its most sophisticated, with a flawless racing pedigree. The XR650R has won every Baja 500 and Baja 1000 it's entered, as well as the once-in-a-lifetime Baja 2000--all in totally dominant style.

But of course we've saved the best for last--the Honda CRF450R and now the CRF250R. The 450 has turned the world upside-down when it comes to prejudices against four-strokes. In 2003 Honda's Ricky Carmichael's incredible win streak in AMA 250 motocross--21 overall victories in a row--was finally broken by the only bike up to the task, the four-stoke CRF450R. Flat track racers have discovered the CRF for short-track events, and it's hardly unusual to see the first two and even three rows mounted on the big CRFs. And the newly rediscovered Supermoto? Owned by CRF riders, who won the inaugural event.

Sure, the CRFs use Honda's revolutionary aluminum motocross frames. But a peek inside the engine provides the real answer. In many ways, the CRFs are the most sophisticated engines Honda offers for sale to the public. Then there's the CRF's unique Unicam cylinder head. It features a single camshaft that directly actuates two intake valves, and employs a forked, low-friction roller rocker-arm. It's a setup that's compact, light, strong, and revs like a four-cylinder sport bike's engine.

While the new CRFs might be sitting in the spotlight today, you can see that rather than standing out, they simply stand at the head of a long, line of Honda four-strokes that have risen to greatness and shown the way in off-road riding. The new CRF250R? In many ways, it is the most advanced of the bunch.

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