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Big Bore

INSIDE SECRETS OF BUILDING A MOTO-READY KTM 300XC TWO-STROKE RACER

You live and learn, one dollar at a time. By Jody Weisel The vast majority of my racing life has been spent on two-strokes, but I?m a realist. When the four-stroke revolution came along, I didn?t feel a need to fight it. I have said many times that, if I weren?t a motorcycle test rider, I would be racing a Yamaha YZ250 two-stroke. However, my lot in life is to race and test what’s put before me, and, increasingly, since the four-stroke revolution began in 1998 and went full complement in 2006, the bikes…

WE RIDE CYLINDER WORKS’ KTM 365SXF BIG BORE

It’s no secret that we were disappointed with the 2011 KTM 350SXF. It wasn?t bad; it just wasn?t what we expected. We knew we could embrace the 350cc design philosophy if it were executed properly, because the Austrian company’s basic idea is sound: produce a mid-size, Open-class engine and tuck it into a lightweight 250cc chassis. The ideal 350cc motocross bike should produce around 50 horsepower and weigh 222 pounds. The resulting power-to-weight ratio would make it the ultimate motocross weapon. It s…

HOW TO BUILD AN INEXPENSIVE TWO-STROKE THAT JUNIOR CAN RACE IN THREE CLASSES

At first glance, this machine might make you think that Honda is bringing back two-strokes for 2014, but that isn?t the case. Just looking at this bike, you would never guess that it is a seven-year-old Honda CR85 Expert. Or, that it was bought off of Craigslist for $700. MXA was interested in a cheap, well-used CR85 Big Wheel because we thought that it would be the perfect transition bike for a young rider making the step up from the minicycle class to the big bikes. Imagine Junior getting another year…

MXA TEAM TESTED: MILLENNIUM TECHNOLOGIES KTM 270 BIG-BORE KIT

WHAT IS IT? Millennium Technologies is making a 270cc kit for the 2013 KTM 250SXF four-stroke. This is a straightforward bore and re-plate project that doesn?t cost an arm and a leg. WHAT’S IT COST? $246.70 (bore/re-plate cylinder), $212.93 (Vertex 81mm piston), $60.84 (Cometic gasket kit). CONTACT? www.mt-llc.com  or (920) 893-5595. WHAT STANDS OUT? Here’s a list of things that stand out with the Millennium Technologies KTM 270SXF big-bore kit. (1) Problem. The MXA wrecking crew usually calls…

FOLLOW-UP HOP-UP! MXA REVISITS THE CYLINDER WORKS HONDA CRF270 TOP GET MORE OUT OF IT

Perhaps you recall our test of the Cylinder Works big-bore Honda CRF270 we tested in the May issue. To summarize, the bike was a blast. The big-bore kit catered to a wide range of riders, but we felt that it could be improved. Following the compl etion of our test cycle we discussed our thoughts of the CRF270 with Cylinder Works rep Jay Clark. Jay said, “If you liked that setup, you’ll love what I have in store for you next.” A few weeks later we met at Glen Helen to re-test the bike. Already quite sati…

WE RIDE CYLINDER WORKS’ BIG-BORE HONDA CRF501

When it comes to building or rebuilding a Honda CRF450 , the MXA wrecking crew has several options. First, we could go with OEM-spec engine parts for a freshly rebuilt 450cc engine. This is the most common rebuild, and it breathes new life into a tired warhorse. Second, we could take the opportunity during the rebuild phase to add a little extra oomph to our CRF450 by going to a fairly straight-forward big-bore 470cc kit with a new cylinder, rings and piston. We could have done either of these things, b…

WE RIDE CYLINDER WORKS’ BIG-BORE KAWASAKI KX269F

It’s easy to think that Cylinder Works is pandering to cheaters with their line of big-bore engine kits. There is no doubt that cheaters are drawn to what Cylinder Works has to offer, but, in truth, most big-bore engine kits go to riders who are not bound by displacement rules (Vets, play riders and offroad racers). However, there could be just a hint of pandering to cheaters in that you can?t tell a 269cc Cylinder Works cylinder from a stock-bore OEM cylinder. (They even put the same casting numbers on…

IN SEARCH OF MORE POWER WE BUILD A 280cc KTM 250SXF MOTOCROSS BIKE

This story is much more about an engine than about the bike itself. More specifically, it is about the trend that this engine represents. KTM’s 2012 250SXF engine is an advanced, 248.6cc, water-cooled and fuel-injected mechanical marvel. It was developed to incorporate Keihin fuel injection, digital mapping, electric starting and a hydraulic clutch. It is a trendsetter?in more ways than one. Can you tell that it is a big-bore? We can, but to the casual observer there is no clue. However, the guy in the …

MXA’S 2012 HUSQVARNA CR144 MOTOCROSS TEST: IT’S LIKE BUYING TWO BIKES FOR THE PRICE OF ONE

Q: ARE THE 2012 HUSQVARNA CR125 AND CR144 THE SAME BIKE? A: They are the same bike, but both start life as a CR125! When you buy a CR125 in the USA, Husqvarna automatically includes the 144cc kit with the necessary cylinder, head, piston and gaskets. Ten years ago, the CR144 would have been considered a cheater bike, but for the current races that average consumers enter, the 144 is often a legal option. For our test, the MXA wrecking crew skipped straight to the CR144 kit in order to run the Husqvarna …

TWO-STROKE TEST: MXA BUILDS A YAMAHA YZ144 BIG-BORE MOTOCROSS BIKE

The plight of the Yamaha YZ125 brings a tear to the eye of every MXA test rider. For 14 out of the last 17 years, the YZ125 has been the best 125cc motocross bike made. Unfortunately, with the advent of the 250cc four-stroke, the YZ125 has been pushed to the brink of extinction. Six years ago, we asked Yamaha to consider building a 150cc version of the YZ125. Yamaha refused on the grounds that the distributors in other countries would not sign off on the YZ150 project. KTM, which just happens to be in o…

TWO-STROKE TEST: WE TURN OUR KTM 250SX INTO A KTM 300SX BIG-BORE

As the niche marketing specialist of dirt bike manufacturers, KTM has a wider variety of models than Baskin-Robbins has flavors. However, the model you won?t see at your KTM dealership is a motocross-specific Open class two-stroke. The KTM 300XC (cross-country) model is close, but ultimately not as good as the 300SX kit for racing. After spending a couple years holding our own against 450s and blowing the doors off 250Fs on our aged 2010  KTM 250SX , the MXA wrecking crew’s primitive instincts took…

THE MXA WRECKING CREW BUILDS A HONDA CRF264 PROJECT MOTOCROSS BIKE

   What’s unique about this MXA project bike is that it wasn?t possible a few months ago. In the past, the MXA wrecking crew has had phenomenal success with big-bore engines?with the sole exception of the Honda CRF250. From its inception, the CRF250 has defied the hop-up mavens? attempts to make it big. It isn?t that building a big-bore CRF250 isn?t a good concept, it’s just that from 2004 to 2009, it couldn?t be executed. Honda’s cylinder liner was barely thick enough to contain the forces of…

WE RIDE THUMPER RACING’S BIG-BORE YAMAHA YZ310F

The YZ310F wasn?t built for a chassis test. MXA left the suspension stock. The motor, on the other hand, was a three-grand endeavor, not including the Hinson clutch and titanium FMF exhaust. A quick look at the specifications of Thumper Racing ‘s Yamaha YZ310F makes it obvious that this isn?t your standard big-bore engine kit. Oh, don?t get us wrong, it starts out like all big-bore engine kits?with a desire to close the power gap between a 250cc four-stroke and its 450cc big brother. The hope of every b…