A Look At the Fabulous Honda Rc125

A LOOK AT THE FABULOUS HONDA RC125

No Exotic Materials, Just Exotic Design That May One Day Be Production.

Fernando Belair

EVER WONDER what's really behind those super fast factory 125 Hondas? What it is that makes them go and go, race after race? Well, you'd be surprised at how close to stock the modified Elsinores are and how far from stock the red "Fire Engine" works bikes are,

The Honda team began the AMA 1 25 National Championship series on their modified production bikes. According to everyone we asked, these rockets had little more than ported barrels, larger carburetors, special exhaust pipes and forward-mounted shock conversions. These are all modifications that can be obtained by the average racer if he has enough cash to pay for what he himself cannot do.

It was on these machines that ttie team began its dominance of the AMA series. But after the first couple of races, the works bikes arrived from Japan. And they were very different. A little slower than the hopped-up production bikes, but much better handling, if you can imagine a bike that handles better than a 1 25 Elsinore. And it was on these bikes that the.Honda team finished the series, taking 1st (Marty Smith), 2nd (Bruce McDougal), 3rd (Chuck Bower), and 4th (Mickey Boone). To top the whole thing off, the team finished every race entirely intact. Not a single DNF for any rider. Impressive!

The machines that sewed up the crown for them, and on which they’ll be competing in future important events, have been dubbed the “Fire Engine” machines because of their color. The bikes are entirely red. Frames, tanks, fenders, side panels, the works. The frame, naturally, is made from chrome moly. The swinging arm is aluminum a very light. Splitting above the now centralized exhaust port, the single downtube frame forms a double cradle beneath the engine, continues back to form the footpeg mounts and then sweeps upward to become the upper shock mounts. The two loops finally join again as the rear fender brace.

One of the major improvements over the standard bikes is suspension. While the riders believe that the steering geometry has not been altered, the front

forks provide nearly eight inches of travel. And most importantly, the forks are of very thin castings that, along with the magnesium front hub, make the front end very light. The rear shock absorbers contain no springs. They utilize pressurized nitrogen in place of the spring, while conventional oil handles compression and rebound damping. The shocks are mounted several inches forward of the standard position, thus providing more than seven inches of rear axle travel. Not only is this a tremendous amount of travel, but the gas/oil shock delivers a much smoother and more-easily-controlled ride than regular spring/oil shocks do.

Like the front hub, the rear unit is also of magnesium, and both wheels are laced to D.I.D. rims. Tires are a matter of personal preference. For example, Smith’s bike has Trelleborgs, while Boone’s is shod with Bridgestones.

The engine is unique. It sports both reed-valve and piston-port induction. Honda calls it Case-Reed Induction. The reeds are vented directly into the crankcase. The intake port is located in its normal position. Intake begins with the first upward motion of the piston as the reeds immediately pop open. Then, as the piston skirt clears the lower edge of the intake port, regular intake begins. On the downward portion of the piston’s journey, the closing of the intake port means the end of intake altogether. Thus, Honda has been able to get full use of the intake vacuum created in the crankcase, while maintaining reasonable port timing with regard to the duration and termination of the intake cycle.

With such an intake arrangement, the exhaust pipe becomes extremely critical to the performance of the engine. In order for the piston’s up-stroke to open the reeds while, in fact, there is a direct passageway still open between the crankcase and the combustion chamber (the transfer ports), there must be a positive pressure wave in the exhaust pipe at this point in each engine revolution. Positive pressure exists in an exhaust pipe when the difference between the internal cylinder pressure and external cylinder pressure is one of attraction, the lower outer pressure drawing out the gases from the higher inner pressure. This insures that as the piston moves upward, and creates a vacuum in the lower end, the reeds will open to enlist fresh mixture, rather than having burnt gases return to the crankcase via the transfers.

While these machines, and the 250cc bikes (which have gas/oil suspension in the front, as well), are very expensivein that they are handmade prototypes— it is hoped that what Honda learns from

these unique racing machines will someday find itself onto a production bike. I don’t know about you, but I can hardly wait.