[technicalities]

[TECHNICALITIES]

GORDON H. JENNINGS

EXPERIENCE IS quite properly regarded as a great teacher, and my first full season of road racing has been very instructive. As some of you may recall. I acquired a Cotton Telstar early in 1964, and that machine was used to launch my racing career. The Telstar, which is a Britishbuilt “production" road racing bike, was not a bad beginner’s machine, but had certain handling peculiarities and was somewhat down on power compared to others in the 250cc class. In a sense, this was a good thing, because it pushed me into experimentation that would not have been done had the bike been completely satisfactory as delivered. And, without the experimentation, several worthwhile bits of information would have gone undiscovered.

The Villiers Starmaker engine, in stock form, had 25 bhp, which is not bad for a 15 cubic-inch two-stroke but not quite good enough in today’s competition. This power deficiency proved to be easy to remove. The Starmaker engine was fitted with a 38mm carburetor and a “tuned” expansion chamber exhaust system, and the port timing extended by inserting a spacer under the cylinder. After these changes were made, the low-end torque largely disappeared, but there was a good deal of power available from 7000-9000 rpm. In fact, with these changes, the output was raised to slightly over 30 bhp.

Unfortunately, 9000 rpm proved to be the complete undoing of the engine’s connecting rod big-end bearing. The rollers would go flat and the rod itself would turn almost blue from the heat. Villiers supplies the answer to this problem in the form of a more sophisticated cylinder and assorted engine hardware, which will boost the Starmaker engine to 31.5 bhp with a maximum of 8500 rpm — and by holding that limit the engine can be held together. These parts were made available to me, but were not put to use, for the very simple reason that I am too heavy, and not sufficiently experienced, for the fiercely competitive 250cc class in AFM racing.

My size is not so much a handicap in the 350cc class, and I found a ride on a Webco 350-kit Honda Super Hawk — which was very much to my liking. However, here again there were a few problems. The converted Super Hawk was a trifle heavy and did not handle too well. The Honda has its rear swing arm pivot mounted on a rather narrow box (which is also the rear engine mounting) at the back of the frame. When cornering well heeled over, the impact from road surface irregularities does not come straight up at the wheel but from the side. The Honda frame is rigid enough for any kind of touring riding, but in road racing the narrow-based swing arm mounting causes a side-flexing of the swing arm. and the rider feels this as a somewhat unsettling twitch. And. too. the standard rear suspension dampers are not adequate for road racing. The overall result was that I found myself riding two motorcycles that did not handle properly.

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The Cotton's handling problems were solved by installing Honda Hawk forks, in which the standard springs were retained but filled with 30W oil for heavier than standard damping. This change will make any Hawk handle better, but at some expense to riding comfort. The Honda's handling problems can. we found, be solved by adding braces around the box at the back of the frame and by replacing the plastic bushings in the swing arm pivots with identical parts machined from bearing bronze. The stock bushings are, again, sufficient for touring but the high loads of racing soon hammer them open. After a few races, the swing arm will pull back and forth about an inch at the axle, and that is not at all good for handling.

Taking stock of the whole situation, we finally decided to combine the wonderfully strong and light Cotton frame with the Honda engine and front forks. The forks had, of course, been added to eliminate the front end waggle that was so pronounced with the Armstrong forks fitted as original equipment on the Cotton. It also seemed an excellent idea to retain the Cotton's very light hubs and 19-inch alloy wheels. With today’s fantastically sticky tires, cornering speed becomes a matter of rider courage and the amount of lean that clearance will permit. The Honda engine is comparatively wide, and the 19-inch wheels would give us just a bit more clearance. So. what we ended with was a Cotton Telstar with a Honda engine and front forks.

The installation job was surprisingly simple. We trimmed out the frame tubes that extend down from the steering head and form an engine cradle, leaving approximately 10 inches of the down tubes. These down-tube stubs were used to hold the mountings that bolt to the Honda cylinder head lugs. At the back of the frame, just in front of the swing arm pivots, we added a box into which the rear engine mounts are bolted, much like the arrangement on the Honda frame. The whole job was done in a few days, and was not as much work as is required to make the modifications necessary to get equivalent handling with the Honda Hawk.

Actually, even after installing the Honda forks, the Cotton was a bit twitchy at times. While trying to cure the problem that ultimately proved to he due to the Armstrong leading-link forks, I had changed rear springs and dampers several times and without knowing it had wandered far afield. After the installation of the Honda forks, more experimentation was done, and I finally reverted to the springs and dampers that came with the Cotton originally. The dampers do virtually nothing on bounce, but act very strongly on rebound, and an investigation made into the situation indicates that this is just the thing for road racing. The make of damper used, incidentally, is Girling, and some of the lads racing modified Super Hawks have found that these do wonders for the Honda, too. It seems worth mentioning that the same type of Girling dampers are used by Honda for their special racing bikes.

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Much of the preceding information the average reader will find of limited usefulness, or interest (except those who want their Super Hawk to handle like a GP machine) but we have gone into some side projects that might be of value generally. One of these was in the matter of brakes. Road racing places great demands on a motorcycle’s brakes, and we were to find both the Honda and the Cotton lacking in this regard. Of course, with the greatly increased speeds obtained with the Honda engine in the Cotton it was only natural that the Cotton’s decidedly puny front brake would be overloaded, but we were a trifle surprised to find that the 8-inch Honda brake wouldn’t do the job either. Once again, the Honda performs quite well as a touring machine and, indeed, has exceptional braking in that sort of use. But, as it developed, the Honda brake, no matter what linings were used, would fade badly under the repeated heavy, high speed applications of road racing. Apparently, the drum and liner are too thin to avoid overheating and distortion.

The answer to the braking problem is the new 7-inch, double-leading shoe “Motoloy” unit fitted to the latest Cotton Telstar. I had one of these flown in from England as soon as they became available, and am very pleased with myself. The Motoloy brake is not very large, but has an extra-heavy aluminum drum. The backing plate has large, cast-in air scoops and the back of the drum is ventilated as well. Competition linings are fitted to cast aluminum shoes, and they truly do the job. As was the case with the smaller brake, adapting to the Honda front forks was quite easy. The axle is the right diameter, and so the drum slips right into place. A couple of spacers were required with the smaller brake, but the 7-inch Motoloy brake was just .065" too wide, so I turned that amount from the side of the backing plate. I should mention that these Motoloy brakes are to be distributed in the USA by Pacific Basin Trading Co. (one of our good advertisers) and that they will retail for about $50.

Another little item I found in my search for parts that would withstand the rigors of racing was the Barnett clutch. These are made for many different motorcycles and while I cannot personally vouch for the Barnett clutch's effectiveness in all of them, it certainly works marvelously in the Honda. When one adds power, with a 350cc kit, etc., the Honda clutch is simply not up to the task; it will slip. This can be cured by increasing spring pressure, but you will then find the clutch almost impossible to completely free. The Barnett clutch for the Honda will take the power, and will also disengage when that is what the rider wants.

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Engine work still continues, and I think we are getting somewhere, although not very near the limit of the Honda CB-77 engine’s potential. The Webco 350 kit has given us a big boost, but we have discovered that one does not merely pop in the liners and cylinders and forget about it. Nor will a “hot” cam work in a completely trouble-free fashion without a bit of help. Finally, there are many little things (aren’t there always) that can be done to increase power and reliability.

The 350 kit will be reliable only if the engine is adequately lubricated. This means, above all, that you must check the oil pump for signs of wear. Those small pump gears will develop too much side clearance, and the oil will leak back past the gears fast enough to seriously affect pump delivery. The Honda shop manual (you should have one of these if you plan to do much to the bike) tells what to look for and the various tolerances. Also, if the kit is being installed in an engine that has “blown,” all oil passages must be cleaned, along with the filter.

There is no completely satisfactory answer to the cam and cam-follower problems that arise. Honda’s followers often have a slight misalignment between the rocker spindle axis and the face of the follower shoe, and this causes a sort of line-contact at the cam that can cause trouble with heavy valve springs and a cam that gives high valve opening rates. Coating the cam and followers with Lubriplate, or one of the molybdenum disulphide compounds will help, as will having the followers stripped and rechromed with a thicker hard chrome-plate.

As for the engine modifications that I have found to give more power, those will be outlined (along with a few things others have discovered to be effective) in next month’s issue. •