[technicalities]

[TECHNICALITIES]

GORDON JENNINGS

THE WORD HAS come down from Olympus. In 1969, we shall have a 350cc limit for Amateur and Expert AMA racing events. But, will we ever see that new limit come into effect? Probably not, and for one very good reason: under a 350cc displacement limit, the two-strokes would surely win everything — just as they now dominate the 250cc class.

Not that four-stroke engines cannot compete with the "ring-dings." Given enough cylinders, camshafts and valves they can hold their own in racing very nicely. Unfortunately, the economic strictures imposed by mass-production will not allow the manufacturers of four-stroke engines enough design freedom to be competitive. It is simply not feasible to build, in quantity and at a reasonable price, a touring bike with four or more cylinders and twin overhead camshafts — about what woul.d be required to match the power of the two-strokes we could expect to see by 1969.

Three years from now, it seems certain that all of the major manufacturers of two-stroke engined motorcycles will have adopted rotary valves, and will be building disc-valve twins. Now then, it takes little imagination to see that a disc-valve, twin-cylinder touring engine will need only special cylinders, big carburetors, expansion-chamber exhaust pipes and a bit of trimming on its valve discs to become a full-fledged racing engine. On the basis of what is being done today, it would not be unreasonable to expect 50-55 bhp — with the power spread to be compatible with the AMA-stipulated 5-speed transmission.

A 350cc, four-stroke twin, even if given dual overhead camshafts, is not likely to match that power. It is by no means as easy to build a four-stroke touring-type engine with a lot of racing potential as is the case with two-strokes.

On the face of it, this might seem to indicate a bleak future for racing; onetype races are of little interest to anyone. However, there is a way out. The twostroke engine does not respond very well to scaling-up; that very powerful and reliable disc-valve 350cc twin will in all probability turn into a real problem child at 500cc. Big two-strokes — that is to say, the 250cc singles — seem to be stalled at about 32 bhp, which would give 64 bhp if you grafted a pair together to make 500cc twin. That output is well within the capabilities of an overhead camshaft, fourstroke engine. In fact, taking into consideration the design limitations imposed by economics, twoand four-stroke engines of 500cc displacement would probably be quite evenly matched. Any bets about a 500cc limit for the AMA in 1969?

Apart from the business of the 350cc displacement limit, which will probably never come into effect anyway, the AMA voted to drop their ban on double overhead camshaft engines. A good move, as the new Honda 450, which will soon be puttering around the public roads by the hundreds, has a twin-cam engine. Also, the AMA specifically approved the 450 for Class "C" competition, and we shall soon be seeing the "big" Honda in action — probably primarily in road racing. Here is where everyone will find that a twincam engine is not, in itself, any guarantee of success. In time, the 450s will make their mark in American racing, but initially at least, existing equipment will have the edge. A factor here is that all development on the CB-450 will have to be done by individual enthusiasts; Honda has shown no interest in American racing and unless there is a sudden change in their policy, Honda supporters will have to do all the supporting themselves.

Down at the bottom of Page 8 of the AMA Competition Committee minutes (for the meeting held on October 31, 1965) there is a paragraph fraught with implications. It states: "It was moved and seconded that the rule covering frames used in Road Racing be changed to: 'Frame must be the same as submitted and endorsed by the manufacturer and/or all USA distributors of the motorcycle to which the frame is fitted. Photos of installation and specifications must be submitted to the AMA Technical Committee to establish approved status'." This motion was carried 25-0.

To see what it all means one may refer to the rule regarding brakes, which is worded almost exactly the same. In effect, what the new frame rule says is that, as in the case of brakes, you will be able to use anything — provided that the manufacturer or distributor will cooperate. So, in the future we shall be seeing AMA road racing equipment with everything except forks and engine specially constructed, and those exceptions will be considerably modified.

Around CYCLE WORLD'S offices (and especially in the Technical Department) all of these changes are regarded with complete approval. The more liberal rules will make racing more interesting, and safer to the extent that the improved handling resulting from freedom in frame design will lower the accident rate.

Had the AMA left the whole thing wide-open for every amateur experimentor, the effect might have been very bad. What they have done, by insisting on what amounts to manufacturer or distributor approval for special frames, is to more or less guarantee sound design and construction.

Anyway, the AMA is relaxing what has been an iron and often unfortunately restrictive grip on racing, and for that we can all be pleased. It appears inevitable, too, that there will be a further relaxing of that grip. Indeed, the AMA's outlook has become so progressive over the past couple of years that if it continues, I shall soon be left without anything of consequence to criticize. Even as matters now stand, I personally will renew my AMA membership and competition license in 1966 with much more pleasure than has been true in the past. The pleasant feeling will come from knowing that my money and (in theory) allegiance are going to an organization that, at last, more nearly represents the realities of this decade, and the wishes of those directly involved in the sport.

(Continued on page 28)

Getting good brakes has become one of the major problems facing anyone building a road racing motorcycle. Here in America, the custom is to use converted Norton Manx or Matchless G-50 brakes, or MotoTech or Gunter disc brakes. Italian Oldani drum-type brakes are often used on lightweights, but the bigger Oldani units are very rare. The disc brakes mentioned will do the job, but they have not been entirely trouble-free and most riders and tuners still prefer the simple and reliable drum-type brake when a suitable example is available.

Those who have had problems with braking will be delighted to know that that there is a new brake being made for racing. The firm of Fontana Daniele, at Via Carlo Torre 28, in Milano, Italy, offers the "FD" brake. These are made in two sizes: 235mm (9.25") diameter; and 265mm (10.43") diameter. Both sizes of front brake are of the dual-drum type, and have four leading shoes. The rear brakes have two leading shoes. We have no information regarding price, or how long you might have to wait for delivery, and there is (to our knowledge) no American agent for the FD brake. The brake is mentioned here because it is being made, and on the basis of such evidence as we have (admittedly scanty) it appears to be an outstanding bit of racing hardware.

(Continued on page 30)

Another outstanding bit of racing hardware is the Yamaha TD-1B. You folks may not have noticed, but the Yamahas won almost everything this year, from the big AMA National-level races right down to local club events. And, all this was done with a motorcycle that needs no special "fettling." Indeed, it seems that the TD-IB performs best in as-delivered form. The handling can be improved by changing to Girling rear suspension units and by replacing the "plastic" swing-arm pivot bushings with parts made of brass, but the engine/transmission unit needs nothing more than routine maintenance. My Yamaha has finished every race in the 1965 season except one, and that retirement was caused by the clutch-adjustment cover coming adrift. The ensuing oil leak lubricated the rear tire, which seemed reason enough to retire at the time.

The TD-IB does have a few sensitive points. The piston-pin bearing is one: running past the red-line (10,500 rpm) will overstress the needle-rollers' cage and it will shatter. Another point to watch, and this applies to all two-strokes, is that there is enough chamfer around the exhaust port window, and that wear has not formed any sharp edges. Either the edges or insufficient chamfer will cause ring breakage. Ignition timing is fairly critical, from the standpoint of power, but the engine will stand a lot of advance before it holes a piston. Piston seizures, the bete noir of two-stroke engines, do not occur. The timing on my TD-IB slipped once, and I ran a 50-mile race with the engine detonating horribly and fingers curled over the clutch lever. Astonishing though it may be, there was no seizure; the piston crowns and cylinder heads were badly pitted, but the pistons continued to move up and down. Apparently, those all-aluminum cylinders (with chromed bores) always expand with the pistons.

It may be of interest to all two-stroke tuners to know that best performance and reliability have been improved with higher percentages of oil in the fuel. On either Francisco "Two-Snapper" or Shell SuperM, a 16:1 mix does the job very well, and we go to 14:1 when the weather is warm. Mix ratios below 14:1 are likely to create problems with plug fouling. ■