Spagthorpe Motorcycles

Classic Spagthorpe:
Pug: The Original Spagthorpe

With all the recent talk about the various Spagthorpe models, I am surprised that no one has mentioned the original Spagthorpe, the Pug. It is a relatively little-known motorcycle, so perhaps it should not be surprising that no one else has heard of it. It is, to be sure, one of the most fascinating episodes in the history of motorcycling, both because of the remarkable design of the machine itself, and of the incredible sequence of events that took place that one fateful Sunday afternoon.

To truly understand the Pug, it is first necessary to understand the men that built her. One must understand that in those days, minimalism wasn't simply the right thing to do—it wasn't even a word. Nonetheless, it was a philosophy that the designers understood all too well, particularly the chief designer, Hairy Rasterhead. Minimalism was, for Hairy, an obsession. So much so, in fact, that he could see no point in having different names for his two main assistants, and so hired two very capable engineers, both named Chuck. Although on some occasions, such as when going into town on Saturday nights, he was heard to introduce himself and his assistants thus: "Hi, I'm Hairy. This is my helper, Chuck, and this is my other helper, Chuck," he generally just referred to the pair collectively as "Chuck" . But I digress.

Although there are no known remaining photographs of the Pug, if indeed any were ever any taken, much about its design has since been pieced together from several first hand descriptions that were written at the time. The engine was apparently taken from one of the early airplane engines, both having been built sometime in the 1890s (the exact year is not known). The most unique aspect of these engines was that, rather than the cylinders being fixed to the frame, and the crank free to rotate, the crank was attached to the frame, with the cylinders free to rotate about the crank. The beauty of this system, as it was applied to the Pug, is the way in which it facilitated the most singularly simple drive mechanism that has ever been conceived, before or since. The crank was attached to the frame at the location where today the rear axle is found, at the end of the rear fork, except there was no swing arm as such, it being a rigid mount. (The frame itself was, however, handcrafted of seasoned hickory, which offered some measure of absorption of bumps.)

The two halves of the fork were set fairly wide apart, as was necessary since the cylinders rotated in the space between them, just as the rear wheel does in a modern motorcycle. The crank had a single "throw" , to which two pistons were connected via a pair of very unique and ingenious connecting rods. It has been reported that the rods were, curiously, manufactured from military-spec eating utensils, with one forked and straddling the other, permitting the two pistons to orbit in the same plane, centered in the space between the rear forks. This arrangement has variously been referred to as the "one forked and straddling the other, permitting the pistons to orbit in the same plane" arrangement, or the "missionary" arrangement, or, more simply, the "humping-couple" arrangement. But I digress.

The two cylinders were opposed (180 degree offset) to one another, and connected to each other via a rigid cast-iron block, which rotated on two bearings on the crank, located at either side of the crank throw, and each just inside the fork. As the pressure in the combustion chamber increased, the pressure against the head caused the cylinders to rotate as they pushed away from the pistons, which rotated along with the cylinders, but pulled away from the heads in doing so since the center of their circle of rotation, the crank throw, was offset from the center of rotation of the cylinders, the crank itself.

On one side of the cylinders a single magneto winding was attached, the pulse being generated by a permanent magnet attached to the crank. On the other side of the cylinders a small cam shaft was connected to the crank via some gearing arrangement that caused the cam to turn at precisely half the rate of the cylinders. It is not known exactly how this was done, but it is believed that this was the only toothed gear arrangement to be found anywhere on the machine. A pair of exposed rods for each cylinder were driven by this cam; these rods actuated the valves via a set of rocker arms, also exposed.

It is not known how the fuel tanks were connected. There may have been a single tank attached to the cylinders, but since this problem was also solved in the airplane application, it can be assumed that it was solved here in a similar fashion.

The wheel consisted of a forged iron ring bolted to the ends of the cylinders, with two additional supports running from the ring to the block, each centered between the two cylinders where they connected to the inner surface of the ring. A solid layer of hard rubber was then riveted to the metal ring.

Here, then, was the beauty and the elegance of the Pug design: neither chain drive nor shaft drive, but *direct* drive. Simplicity defined, pure and, well, simple. There was no shaft effect, and no chain to rattle around, stretch, and generally make a nuisance of itself. Neither before nor since has there been another design so elegant and so, well, simple.

The diameter of the wheel was about half a meter; the circumference about 1.6 meter. At about 400 rpm, the machine reached its top speed of about 640meters/minute, or 24 mph. Due to the large moment of inertia of the rotating part of the engine, it idled at 200 rpm. To start the bike, one simply ran alongside until the speed reached about 12 mph, at which it point it would start and you simply jumped on. It was, to be sure, the very of essence of simplicity.

Sadly, though, this was a machine well ahead of its time, and did suffer from several minor technical difficulties. First of all, there was the difficulty climbing hills. The engine itself was actually capable of more power than could be used (on level ground). The work required increased more rapidly with velocity and rpm than did the power generated, so that above 400 rpm, the incremental power required was greater than the incremental power generated. It was consequently unable to climb hills with slope greater than about 5 degrees, requiring the rider to frequently dismount, run along with the bike for so long as it would continue under its own power, and eventually push the bike when it died as the slope became too steep.

More serious than this drawback, though, was the torque reaction problem. The moment of inertia of the bike, about the crank, was very small, due to the fact that most of the mass of the bike was contained in the rear wheel. Even the feeble amount of torque generated was enough to cause the front end of the bike to come off the ground during modest acceleration. It was generally necessary to build the speed up very slowly, taking it from 12 mph to 24 mph over a period of several minutes. Even without the weight transfer of acceleration, the reaction to the engine torque alone was sufficient to cause the weight on the front wheel to be too small to generate sufficient steering force and stability.

The person who discovered the solution to this problem was, remarkably enough, the test rider, Scratchin' Itches-Fetching Ping Pong Balls (who was referred to by Hairy as simply "Scratch" ). Scratch took one look at the situation and proclaimed, "If you turn that there wheel around the other way, the torque reaction will reverse, transferring the weight to the front wheel. Turn that there wheel around the other way." The only problem with this was, of course, that the machine would now run backwards, with the steered wheel following the power wheel. This required the rider to turn around and face the other direction, and steer the bike by reaching around his back. This was a lot like steering a small boat with an outboard motor; you had to move the steering arm in the direction opposite to the direction that you wanted it to go, thus the term "counter-steering" was born, although it is still generally misunderstood even to this day.

The steering problem was partly solved by extending the handlebars further, so that they came up along either side of the rider. This limited the extent ofthe steering rotation, though, but Scratch, being the resourceful dude that he was, soon learned to increase the extent of the steering rotation by leaning off to one side of the bike, a technique that he referred to as "hanging off" , and that is still practiced to this very day by many of his modern disciples.

The reversed-direction solution worked fairly well, with only a minimal amount of traction loss at the power wheel, which was referred to as "torque steer." The only remaining significant problem was that the trail of the steering wheel was now in the wrong direction. This was solved by merely using a near-vertical rake angle and a large amount of negative-positive (positive-negative?) offset in the front (make that rear) triple clamps.

And thus was the Spagthorpe Pug born. A truly remarkable motorcycle, to be sure. Test runs went pretty well for the first few weeks, consisting primarily of low-speed runs back and forth to determine the handling characteristics. Scratch, however, grew increasingly impatient to attempt to set a new land speed record. Hairy and Chuck did some calculations and were convinced that the engine would actually generate greater power if only there were some way to get the rpm up higher.

Exactly what happened next is not clear. The few surviving accounts of what happened that fateful Sunday afternoon disagree to various degrees, but it seems that what happened went something as follows. Once again, it was Scratch who had the breakthrough idea. He realized that if the bike was ridden downhill, the force of gravity would add to the acceleration generated by the bike, causing it to go faster, which would increase the rpm, and permit the engine to come into its power band. So they pushed it to the top of a dirt road that wound up the side of a mountain. And then they started to push it down, and Scratch jumped on, and Hairy and Chuck stood and watched in amazement at what happened next.

The bike took off like nothing they had ever seen before, accelerating even harder with every incremental increase in speed. Faster and faster, reaching 30, 40, 50 mph and beyond, still accelerating. 60, 70, 80 even 90 mph, now shaking violently. The acceleration began slowing, though, and gradually it hit 95 mph, and then slowly 100, 101, and 102 mph. Chuck realized that Scratch was rapidly approaching Dead Man's Curve, and they yelled at the top of their lungs, while Hairy simply stood and watched in amazement, completely dumbfounded.

Scratch reached 103 mph, and then, barely, 104. Exactly why Scratch didn't make the curve isn't clear. Some speculate that the excessive inertia in the wheel made it impossible for the lean angle to be increased sufficiently fast. Regardless, Scratch did miss the curve, and at the same instant he went flying over the edge of the cliff, the Pug hit, yes, 105 mph: ludicrous speed. Nobody had ever reached ludicrous speed before, much less stopped from ludicrous speed. The wheel and crankshaft broke away from the bike frame, which went with Scratch over the cliff.

The wheel and crank landed, amazingly enough, back in the road further down the side of the mountain. Without the inertia and weight of the frame and rider to resist rotation of the crank, something totally unexpected happened. The rotation of the wheel slowed down, and the crank began rotating furiously. Hairy, Chuck, and Chuck had run as fast as they could down the road, and when they caught up with the wheel, they found it wedged between two large rocks, stationary, with the crankshaft rotating furiously inside. Hairy took one look at it and proclaimed, "Eureka! I have discovered the answer! The cylinders can be attached to the frame, allowing the crank to rotate, and the rotational motion of the crank then transmitted to the wheel by … something!"

As for Scratch, the last words that he was heard to utter as he went flying over the cliff were largely incomprehensible; the only word that Hairy and Chuck could recognize was "champion," but they never figured out exactly what it meant. He was never seen again, and no body was ever found. Curiously, his jacket was found, even more curiously, with not a single scratch on it. Many speculated that since no one had ever stopped from ludicrous speed before, that it might be physically impossible to stop. In retrospect, this logic seems questionable, since in fact no one had ever even reached ludicrous speed before.

Hairy spent the last years of his life trying to perfect his new invention, "shaft drive," as he called it. He was largely confounded by the same basic problems of the direct drive system. His oldest son Chian, however, after watching his father lift his prototype frames countless times with a rope and pulley, hit upon the idea of a flexible drive mechanism, where the rope would be made from metal plates linked together with pivoting pins running across to the opposite plate. Although the proper spelling somehow got lost over the years, there can be no doubt as to the origin of our modern "chain" drive.

As every story must have a moral, so must this one, although you would never have guessed it. Since there is no way that you could possibly have deduced it, I am obligated to spell it out: in the end, what really matters is not what you ride; it's the ride itself.

What was the ugliest motorcycle ever produced? (New, not ratted out.) That is an easy one to answer… the Spagthorpe Pug. This bike was so ugly, that (those of you who are old enough to have voted for/against Carter will remember) Joan Claybrook had the NHTSA take the tail light off it and make it ride-able (sort of) backwards. This is proof-positive that it was the ugliest bike and comes from the maxim, "If my dog was that ugly, I’d shave his ass and teach him to walk backwards."

From: BarberTB (tomb@drutx.ATT.COM)
Subject: Spagthorpe Pug, the original minimalist motorcycle
Keywords: Spagthorpe, Chuck, torque
Date: 1992-08-14 11:50:04 PST
Copyright © 2000, 2001 by The Spagthorpe Motorcycle Company®
Sheldon's Archives