110 / SPORT QUARTERLY deas are formulated in many ways. that weigh approximately the same. I A conversation at a cocktail party, On the fast circuits they are out of a bull session at a race meeting or the business strictly because they lack old-fashioned bench racing that takes the ability to accelerate or match the place any time two or more motor­ top speed of their rivals. With more cycle enthusiasts get together. Lots of horsepower and less weight it would great ideas get passed back and forth be another story. — lots of bad ones too— but often a So why not do just that? We could Don’t seemingly insignificant remark can be build a 500cc four-stroke single that the spark that sets one to thinking develops over 60 hp and house it in a about a particular subject area. Such good-handling package that weighs is the case with our “project.” A good in at around 260 pounds. Why not? friend remarked that “four-stroke For one thing, it is too expensive. For Count another thing, Mr. Petersen is in the singles are dead.” Immediately put on the defensive due to a fondness for publishing business, not the motor­ single-cylinder machines, the only cycle business. So that’s out. But there possible reply was the point blank- is an alternative, and that’s what we i The question, “Why?” decided to do. We would put our col­ Reasons don’t come readily to lective thoughts together and design mind. True, the single was for a long one we thought could do the job. time prominent on the street as well rhumper as the race track. Then, “poof,” it FROM WHERE THE ENGINE was gone. BSA, Norton, Matchless, AJS and Velocette were all popular Then the real head-scratching be­ and certainly had more than their gan. Before any chassis configuration share of race victories. Manufacturers could be finaliTed, the size and shape Out like , Ducati, Morini, Mondial, of the power unit had to be decided. Moto O117.7.Í, and NSU fielded Once we had that, the whole machine extremely competitive singles in inter­ could be laid out. It became TH E big national racing. In the United States, decision, since every other compo­ BSA singles were virtually unbeatable nent’s design would be affected by it. on the dirt tracks. Then manufactur­ Thought was given to borrowing ers all but stopped building them. some of the internal components of The single did indeed wane but not an existing high-performance auto­ from old age. It was factory genocide. motive engine and building a single­ cylinder structure around them. The EVERYTHING BUT POWER whole project began to take on the seriousness that would be connected A comprehensive list of the pro’s with actually building a real engine. and con’s of the single-cylinder design No pie-in-the-sky, far-out design ap­ FOUR VALVES, will find but one major reason for its proaches; just proven ideas that extinction. In its latest form it did not would create a practical design as FUEL INJECTION offer the engine performance that well as adequate performance. AND 60 HP could be had from engines with two It was quite feasible that one- or more cylinders. However, in nearly PUT THE SPARTUS eighth of a super-hot Ford or Chev­ every other area of design that has rolet could be expected to put out SINGLE BACK IN THE proven important to building a com­ approximately one-eighth the power RUNNING WITH THE plete competitive machine, the single of the actual engine. After all, the stands tall. It can be narrower and better V-8’s are developing gobs of CURRENT BATCH can therefore be mounted lower in torque and doing it reliably at 8000 OF MULTI’S. its frame for better handling and less rpm and more with pushrods. One frontal area. It can be smaller and could easily borrow their crankshaft IT’S ONE OF A KIND, lighter for better braking and accel­ dimensions, buy their rods, pistons SINGULARLY TERRIFIC, eration. It can be less complicated and valve gear and build them into a THUMPTHING ELSE! and therefore less expensive to pro­ single-cylinder configuration. The final duce and easier to tune. displacement would be a problem A single suffers only from lower since bore and stroke ratios would BY TONY MURPHY total engine performance. The multi’s have to be juggled, and with them definitely have the edge, but the gap some of the power potential might can be narrowed considerably by be lost. attention to the chassis and suspen­ It was frustrating. No matter how sion. In Europe, Manx Nortons are you looked at it, it was still just day­ obsolete but because of a fine chassis, dreaming — nothing more than a they are still in the hunt on race bench racing session justified by the courses which have a premium on fact that it might be an interesting handling rather than horsepower. story to write, if not read. It lacked Good Nortons develop 50 hp and realism. It was an illusion that unin­ weigh more than 300 pounds, and yet tentionally would be critical of manu­ snap at the heels of 60-plus-hp multi’s facturers who have built singles, and

MOTORCYCLE SPORT QUARTERLY / 111 n o / i mm DPVPi r connT n i i A D T r o i v yet it would never prove its worth— responsible tor building the engine. therefore be lowered with no sacri­ except on paper. No, it wouldn’t be Both men have illustrious back­ fice in strength. fair. If we were to build a better grounds in the high-performance bus­ The timing side of the crankcases, single-cylinder engine to power a rac­ iness, particularly with the world- which in our installation will be the ing machine, we had better build it famous S&VV valve spring covered right-hand side, has an opening just or forget the whole thing. Or we had elsewhere in this book. large enough for an oil seal on the better find one that had already been In the early Sixties they undertook 1-inch diameter shaft. Large alumi­ built. That’s just what we did. to build an all-new Indianapolis race num bearing housings are interference car powered by their own six-cylinder fitted in the crankcase casting and THE “ SPARTUS” SINGLE engine. For test reasons they built a support the crankshaft on both sides 500cc single-cylinder. It ran — still in automotive babbitt inserts. The Dubbed “Spartus” by its builders, docs — ran well. Initial running pro­ main bearing housings and the crank­ it was not really new. In fact, we had duced over 60 hp, and refinements shaft are inserted through a larger seen it before, and if the truth were to camshaft timing and the many opening on the drive side. Rod and known, it might have subconsciously other variables that contribute to ulti­ piston are fitted through the cylinder had an influence on wanting to build mate performance held hopes of per­ bore; car style. the ultimate single in the first place. haps another 8 or 10 on top of that. Split connecting rod is supported Art Sparks and Tim Witliam were But we won’t count on that. YVe had on a 21i-inch automotive-type insert. found our 60-plus-hp single. We could It is an H-pattem Carrillo high- touch it, listen to it run and— best of performance automotive item that has all— we could build our motorcycle proven nearly indestructible in high- around it. revving car engines. Bearing in mind that it was never Oiling is handled by a gear pump intended for a motorcycle, there are driven by the crankshaft and inounted a few things that are less than ideal on the front side of the engine at for this use. Leaving that till later, crankshaft center height. Since the let’s look at the things that it has go­ intent was to have the cylinders in an ing for it. It is small by 500cc single­ opposed position (a la Porsche), the cylinder standards, being some 5 location of the oil pump would have inches shorter than a or placed it at the lowest point on the BSA Gold Star. It weighs about the engine. In this way the oil would same, but could have been consider­ drain down into the pump and assist ably lighter if it had been designed as scavenging. In our application the an air-cooled rather than water-cooled pump is a little too high to benefit engine. Adding to its weight are the from the call of gravity, and some relatively bulky innards designed suitable modifications in this area large on purpose for use in an engine might prove necessary. It could be that was ultimately to be super­ done easily with a remote oil supply charged. But a plus is that extra and would work efficiently no matter 1. Feasibility of using a single­ where the location. cylinder engine to develop a strength is also extra life, making the multi is not new. In addition to engine able to withstand hard use MORE CRANKCASE VOLUME the automotive companies, two- for sustained periods. wheel manufacturers find it the On the opposite side of the engine easy way to go. This little single INTERNAL CONSTRUCTION from the oil pump, the photographs was built to test ideas for World show a small fabricated tower. Initial Champion four-cylinder Benelli. The crankcase assembly and cylin­ testing showed that the lack of enough der barrel are cast in one unit, so it is 2. A sectional side view, right crankcase volume was causing a side, of the Spartus single, reveals probably better described as a block. pumping effect, and the addition of the construction of the unusual A spigoted liner is pressed in from some more volume was accomplished crankcases and rugged simplicity the top, and during initial tests sev­ by using this small plenum chamber. ol the internal components. The eral bore/stroke ratios were tried in Because its function is merely to pro­ overall height of the engine is the same basic casting by using dif­ vide more crankcase area, it could a very short 17 inches. ferent liners, crankshaft and rod take whatever shape became neces­ 1 lengths. The present dimensions meas­ sary to cater to space requirements of 3. Sectioned fore and aft, the ure 32Í inches for the bore and 2% other components. narrowness is impressive. Note for the stroke (95mm x 70mm). the huge, car-type main bearings The crankshaft itself is machined supported in large-diameter alloy Advantages of this type of con­ from 5140 steel, has main bearing housings pressed into the case. struction are many. Normal motor­ journals 2% inches in diameter and is The holes above and below the main cycle practice is to split the crank­ the same shape as an automotive bearings are for through-bolts cases into two halves, either left and crank throw with a small 5,‘2-inch that add to the total rigidity. right or top and bottom, and then diameter at its widest point. An out­ bolt them together around the crank­ side flywheel 8 inches in diameter is 4. Gear-driven camshafts have vernier shaft itself. The Spartus design allows attached to the drive end of the crank liming adjustment. Oil pump is driven from intermediate gear at the crankshaft to be inserted in a by six 5/16-inch dowels. Whatever reduced speed. Water pump could be single robust structure that, because drive method is employed then con­ driven from same gear on the it more closely resembles a sphere, nects on the outside of the flywheel other side of the engine or worked does not require the weighty beefing and is held in place by a 118-inch bolt externally by the drive belt. of separate cases. Overall weight can threaded into the center of the shaft.

MOTORCYCLE SPORT QUARTERLY / 113 116 / MOTORCYCLE SPORT QUARTERLY camshaft bearings are identical at Before we actually put a chassis both ends. So if you had noticed that around the motor, we need some Don’t the intake side seemed to lie jumping means of delivering that power. It around from illustration to illustration, would be nice to adapt a gear-driven Count there’s your answer. transmission but, alas, that would re­ The need to do this was brought quire some means of permanently about in the search for a mounting attaching the engine to the transmis­ The position in the chassis. If it were to be sion housing. This would require a mounted vertically, the exhaust pipe common casting which would make would come up through the gas tank. the whole assembly an in-unit affair Thumper Either that or the pipe must make an beyond our facilities. The only alter­ extremely sharp bend and then re­ native is to chain-drive an existing semble a serpentine in its progress transmission by means of a sprocket Out toward the rear of the machine. If mounted on the outside flywheel. 1. Just how serious the Spartus the engine were laid horizontally, it There is really only one available effort was, is evidenced by the would require that the engine be transmission that would be suitable, number of components prepared for mounted far enough back from the and that is the AMC four-speed unit a test engine. Several cylinder front wheel to allow pipe clearance. as fitted to the current batch of Nor­ head configurations were tried, as Then the pipe would still require ton Commandos. Any Norton or late- well as different bore/stroke some tricky bends and there would model Matchless owner will tell you ratios. Then testing was stopped. not be much room for a transmission they are indestructible, but there are behind the prone engine. Further­ even more important reasons. The 2. This is the order in which the more if this was to be a fire-breathing major components go together. In basic transmission is identical to those our application this would be the model lighter than the competition, used in the Manx Norton and G-50 left side of the engine with the it would require more weight on the Matchless and therefore has dose- head turned around to place the front wheel to keep it from continual­ ratio gears available. In addition, intake up front. Relationship of ly being airborne than either of those there are sets of five- and six-speed bearing housings to crankcase layouts permitted. There was oidy gears made to replace the original can clearly be seen. one choice left. four speeds with no changes to the The crankcase portion of the en­ actual gear cases. With high horse­ 3. Extreme rigidity can be understood gine carries quite a bit of weight so power outputs come narrow power when one realizes that those ranges; with narrow power ranges bearing housings are an inter­ it should be just as close to the front four speeds are just not enough to get ference fit in the cases, and the wheel as possible. This we did, and through-bolts lock them in place. then rotated the engine around the the job done. Five would be minimum Note water passage around cylinder. crankshaft center some 30° to the — six would be ideal. point where it gave adequate clear­ With the dimensions of both the 4. Partially machined castings and ance to the transmission mounted be­ engine and transmission, we can now cylinder head section give a hind and gave the exhaust pipe a set about bolting them together and further clue to the potential of relatively bend-free path rearward. putting a chassis around them. En­ the Spartus as a single-cylinder The intake system then fits snugly gine plates which bolt to both sides of racing engine. Far from being a under the gas tank and is protected the transmission housing and then to back-yard special, it was designed from disturbing air by a combination the engine itself are simple enough to and built by individuals that knew from experience what was needed. of the frame steering head and appro­ fabricate. There are several suitable priately placed ducting drawing air places to attach to the engine; the from above the gas tank and behind water jacket covers and plenum cham­ the forks. ber mount are robust enough to at­ tach a specially made cover with FUEL INJECTION mounting points for the engine plates, but even if they weren’t, some handy Initially tested with fuel injection, surgery with a lidiare could provide this would be retained for the prescrit mounts that would be up to the job. to be replaced by carburetion if it became necessary. THE CHASSIS So far, so good. To this point there can be no argument with the fact As outlined elsewhere in this book, that such a configuration, using an a flex-free frame is the heart of good existing engine is feasible. Based on handling. The forks and rear swing the performance figures of the engine, arm must be equally as rugged so it is probably the most potent 500cc that there is no deflection at all. Add single ever manufactured considering to this a proven overall and only the 60-plus power of its mildly weight distribution, and you should tuned state. With more power, who have a good-handling package, espe­ knows how much, it would certainly cially after minor adjustments here be a competitive machine in many and there. types of racing. So let’s go on as The original concept of our little though we were part of a serious ef­ project had been to design a com­ fort to make it into a raceworthy petitive single-cylinder engine and machine. What’s next? house it in a lightweight chassis that

MOTORCYCLE SPORT QUARTERLY / 117 possessed superior handling qualities. the chassis experimentation that Since it was only to ho built on paper, would surely he necessary. A conven­ Don’t some unique chassis concepts were at tional chassis could he made to handle first envisioned since it is easy to as well, if not better than the compe­ Count speculate on what would Ik? better tition. Besides, the powerplanl could than the current way of doing things. always he installed in a “trick" chassis Hut our discovery of a “living" en­ at a later date. gine turned our thoughts away from The WHERE TO START? speculation and toward genuine pos­ sibilities. Thoughts of exotic mono­ Unhampered by a massive power Thumper coque frames and new concepts in unit, the length of the machine and suspension were put aside in favor of the amount of ground clearance arc a conventional design that would, really flexible. Mounting the engine Out were it really being built, eliminate as close as possible to the ground will

Cycle-ized Spartus would be inclined approximately 30° to place intake and exhaust in suitable positions. Engine would then be attached to suitable transmission, the entire assembly being quite compact due to diminutive dimensions of engine. Intake location would make it vulnerable to air-ramming and foreign objects, but suitable shielding could eliminate the problem. Side benefit would be cool air in this location since normal engines receive intake air after it has passed hot engine.

AH.

/ MOTORCYCLE SPORT QUARTERLY get the weight down low; the length wheelbase and small wheels, together solely by the contact area of the tire. of the wheelbase will affect the re­ with the low overall weight of the To benefit from this, the tires are of sponsiveness of the steering. A figure machine should make it extremely larger-than-normal section, being close of 50-52 inches was chosen for the easy to handle on tight courses and to a 4.00 size. This larger size, com­ wheelbase since the machine would in traffic situations. bined with the fact that the machine be easier to maneuver. Machine for Sixteen-inch wheels have other ad­ does not have to be leaned over as machine, the one with the shorter vantages. The relationship of the cen­ far as its longer, larger-wheeled com­ wheelbase will prescribe a given turn­ ter of gravity of the mass of the ma­ petition, places more rubber on the ing circle with less angle of lean. chine and the contact patch of the road during cornering. Conceivably, Smaller wheels have the same effect front tire can be advantageous to this would leave the rider with more on the turning circle, so we have braking. There is some mechanical left when the other fellows are on opted to use 16-inch tires mounted advantage that should actually im­ the ragged edge, and perhaps with a on lightweight cast magnesium prove braking power, if not stopping slightly modified riding technique the wheels. The combination of short power— a factor that is determined machine could be cornered faster than the competition when riding on its ragged edge.

FUTURE PROJECTS

So we have the wheelbase, wheel and tire size and a general idea of the Exhaust system would be nearly machine’s ultimate configuration. The straight. Conventional pipe Is shown since only testing can engine/transmission will fit within determine most efficient shape. those dimensions, so it remains only Radiator could mount in front of to hook it all together with a suitable engine or other convenient place. tubing and hang forks at the front For road racing use of an aircraft- and a swing arm at the rear. We type skin radiator as part of won't go into the chassis in detail, the streamlining is a possibility. since as we have already stated it would be of conventional design for the purpose of testing the engine’s performance. At this time we wish only to prove the feasibility of using this existing engine within the con­ fines of a motorcycle chassis. If it were to work as well as predictions indicate, then a major effort could be aimed at building an equally ad­ vanced chassis that would further raise the competitiveness of the whole unit with the existing 500cc racing machines. Not coincidentally, we have a chas­ sis project in the back of our heads, the concept of which we feel is long overdue in the two-wheeled world. A full technical report is scheduled to run in the next (Winter) issue of Motorcycle Sport Quarterly. Initially, the designs are aimed at eliminating all that is wrong with existing chassis and suspension systems and replacing them with a concept unaffected by motorcycle tradition. By now you may have guessed that it is of the monocoque type so popular with car manufacturers. That it is, although it is unlike any of the past efforts of machines such as the Ariel Leader and the 25()cc Ossa road racer. It is a true monocoque chassis which performs all of the needed functions of a two-wheeled vehicle, but not in a conventional manner. If that interests you, tune us in in about three months and we’ll try and con­ vince you that it is the basis of the motorcycle of the future, both on the street and the race track. •

MOTORCYCLE SPORT QUARTERLY / 119