Honda's Budget Bullet

HONDA'S BUDGET BULLET

A Production GP Bike for Club-Level Racers

Honda's approach to the sport (or business) of racing has never been like that of the other factories. After years of building upon the basic transportation market Honda went racing in the major leagues. And got drubbed. Honda came back and won everything in sight, setting records that stunned the world then and in some cases still stand today. Then Honda retired from road racing and eased 'way off in motocross.

Then Honda returned, with a works motocross team and top class bikes. Road racing was different. Honda builds over~ powering machines for the specialized field of European endurance events, in which the various English, French, etc., Honda teams have had only each other to beat for two years now.

Late last year Honda made still another return to racing, this time at the other end of the scale. The machine is the Honda MT125R and it is almost a contradiction in terms; a production Grand Prix motorcy cle. Production is maybe too strong, as the first batch of MT125Rs numbered 200, with more to come if demand warrants.

Grand Prix, though, is accurate. The MT is a purely road-racing bike; delivered with a 125cc two-stroke Single, actually the CR Elsinore engine in road-race tune; fitted with a slick little fairing, tiny fuel tank, skimpy seat and streamlined rear section.

The MT has to be one of the most rational motorcycles ever built. Honda's racing and design departments had a nicely defined job. Make a pure racing bike for private owners, using all possible pro duction-there have been enough Elsi nores made by now to call the Elsie thatparts.

The engine was simple. The MT has the CR125 cases, crankshaft, connecting rod, piston, rings and cylinder head.

The cylinder differs slightly, with a larger inlet passage to accommodate the 34mm Mikuni carburetor, 4mm larger than the Keihin fitted to the CR. The rubber connecting hose is a bit shorter than that on the CR, to move the power peak higher. Port configuration, size and timing are the same for both engines.

The MT's expansion chamber is quite different. The tapers of the conical sections are more gradual and the overall shape is less bulbous. The effective length is shorter and in conjunction with the larger carb and shorter inlet tract, gives a higher, nar rower rpm range and a slight (2 claimed bhp) increase in power.

Ihat tells a bit about road racing. Even a modern 125 motocross bike must have some low end, even if it's only to keep the engine running while the rider fans the clutch in the tight stuff. A road race machine need never get off its pipe except at the start, so there really is no low end power at all. None. The tach doesn’t even have numbers below 5 thou.

$1764

A Kokusan Denko CDI unit provides spark for the MT. It’s the same type used on the CR but also powers the MT’s 14,000-rpm electric tachometer.

The MT’s major differences begin at the transmission. Power is transmitted through straight-cut gears, 4:1, with a wet clutch. Internal ratios are completely changed. The road-race motocross gearboxes have nearly the same sixth, while the dirt machine has a much lower, i.e. numerically higher, first. And the MT’s intermediate ratios are much closer together.

This close gear spread is absolutely necessary. The engine must remain within the powerband at all times. Even a pipey motocross bike can use a wider gear spread because wheelspin and the clutch can keep the revs up. On pavement, there’s no way to spin the tires and the clutch won’t last long under such a strain.

Another difference is the cost of replacement. The CR’s internal gears are made in the thousands, which brings unit costs down to within reason. But with only 200 MT125Rs built, the cost of each gearset is high. ’Way up there high, like $600 for the set.

The MT gearshift is also different. The road racer has rearset pegs, behind the shift pivot. The lever goes back to the foot, rather than forward. But the shift pattern is the same. Honda simply built a shift drum with a reversed pattern.

Another few pounds is saved by removing the kick start lever, gears, springs, etc. There’s no kick start because the engine wouldn’t run at foot-cranked speed anyway. What you do is round up your crew and push until the engine fires or they collapse.

The main frame section of the MT appears to be CR; same pattern to the steering head and tubes, etc. The rear portion of the frame is different. The MT is lighter and shorter and lower, so the various pickup points for the shocks, pipe, body sections and so forth are changed. And because the MT is so low and uses smaller wheels and tires, the steering head angle is 27 deg., 4 deg. steeper than the CR.

Front forks are Showa, similar to those used on the smaller XR machines, and have 27mm stanchion tubes. Sounds small but so is the MT and because it’s low and has limited wheel travel, the MT has less flex to fight than an off-road bike would have. The MT also gets its own internal valving, giving more rebound damping than the XRs have.