The Service Department
THE SERVICE DEPARTMENT
GORDON H. JENNINGS
HONDA 350 KITS
I read the very interesting account of the Forgedtrue Company’s kit as applied to the Honda Hawk on page 28 of the Oct., 1963 issue of Cycle World.
Now I wonder if this kit is applicable to the Honda CA-77, 305cc, and if the results warrant the time and expense?
I also note on page 48 of the Jan.. 1964 issue of Cycle World that the Custom Plastics Sales claim they can give the same results for about half the price simply by having the Honda’s original sleeves bored out and fitted with their special pistons.
Now the question that is foremost in my mind at the moment is; by using the Forgedtrue sleeves and boring them to the maximum permissible diameter, just how much could the Honda engine be stretched — volumetrically speaking?
I am quite attached to my ’63 CA-77 Dream, but it just doesn’t have enough muscle to keep up with expressway traffic under adverse conditions. I would like your opinion as to whether it would be worth the time and money to build-in the required muscle?
W. H. Baker Cridersville, California
Yes, the Forgedtrue/ Wehco pistons-andsleeves hit for "stretching” the Honda Hawk engine to 350cc can he applied to the Dream engine. In fact, it is intended for all of the Honda 250/305cc engines, although when converting the small-bore engine, some additional parts changes are necessary.
/ cannot say if the conversion is worth the time and money to everyone. Some people wotdd not use the added power the kit provides even if they had it. One thing is certain: there is a marked improvement in performance with the 350 kit. For best results however, the kit should be used in combination with the Harman and Collins cam, and a Super Hawk cylinderhead should be purchased if the bike in question does not already have one.
The Custom Plastics Sales 350 kit will give approximately the same performance as is obtainable with the Forgedtrue/ Webco kit. There is a substantial difference in price, as I am sure everyone has noted. There is also a substantial difference in the kits. 1 do not believe that complete reliability can be obtained by simply bunging out the bores of a 30.5 (the Custom Plastics conversion cannot be applied to a 250) to take 350 pistons. That would, in my opinion, leave the cylinderwalls dangerously thin — although there is no disputing the fact that 305 engines have had the Custom Plastics Kit installed and they do run.
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Even so, and despite the higher price, my personal preference, especially if the engine is to be used in racing, would be the Forgedtrue/ Webco kit. It is, in every respect, a first-rate package, with forged aluminum pistons, special rings, and new cylinder liners of adequate thickness and strength. As has so often been said, “you get what you pay for.”
My objections to the thin cylinder walls also applies to your idea about boring out the special sleeves provided in the Forgedtrue/W ebco kit. This could be done, and it might work, but you might need special pistons and rings, which might or might not be available without having them made to order — a very expensive process.
TIRES?
I enjoyed your technical article on tires. A few questions on this topic remain in my mind, however.
What tire, short of an out-and-out racing tire costing about $25 (such as the Avon Green Dot) would be likely to give the best road holding in a dry-asphalt corner? Avon Mkll tires had occurred to me, but they don’t look as though they would give much surface area when heeled over.
Pirellis have the “Avon racing” look, but they are doubtless made of low hysteresis rubber (they are certainly inexpensive.) The Dunlop K-70 might be the answer. Also, the Japanese “Yoko” tires had occurred to me. These cost about $18 apiece and are shaped very much like Avon racing tires, but are doubtless made of inferior rubber.
I am interested in the tires you had on that Ducati Diana Mk3 you tested in such a well-heeled (pun) fashion in the December issue. Pray tell what were they? They couldn’t have been Pirellis (at least not the front one) because Pirelli doesn’t make a 2.75-18 rib.
What tire costing $20 or less is there that won’t go bald after 5000 miles (road mileage) and will maintain its grip well heeled over? I am interested primarily at this time in the rear tire.
Vedder A. Wright Davis, California
The tires fitted on the Ducati we tested were the standard equipment Pirellis; and the front tire was a ribbed 2.75-18. We do not know how high or low hysteresis these tires might be, but they did give an excellent grip on the road. I will not try to make you believe that they are as good, in terms of adhesion, as a “real" road-racing tire. However, they were certainly as good as anything we have tried, with the exception of racing tires, on dry pavement.
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The Avon Mk II tire, which is sold in matched sets (rihbed tread for the front wheel; block-pattern tread for the rear) has a high-hysteresis rubber in the tread, and this would offer a substantial improvement over conventional tread rubber on wet roads. Grip on dry pavement would be very slightly better — not enough to be noticeable at the cornering speeds possible with a touring-type motorcycle.
Other tires give approximately the same grip on the road (assuming that the tread pattern is suitable for road use) and the only thing that varies much with price is durability. High-quality, high-cost tires differ from the low-priced variety mostly in materials and level of workmanship. Top grade tires are less likely to develop broken cords as a result of running over sharp rocks, etc., and they have tread rubber compound to resist sunlight and ozone attack. Consequently, there is less weather checking of the side walls, and the carcass will remain serviceable through several re-caps. Also, premium quality tires are somewhat less prone to tread separation when ran for long periods at high speeds. This last is, of course, a rare phenomenon in this country, where speed limits prevent sustained high speed cruising. Finally, most premium tires have a tread compound that is more resistant to abrasive wear, and will last longer than “bargain” tires. Whether the long-wearing properties are enough to offset the increased price is a moot point.
Actually, the service life of a tire depends a lot on the rider. If inflation pressures are maintained per specifications, and if the rider does not make drag-strip starts and hard cornering a habit, almost any tire will last 5000 miles. Conversely, han riding can scrub any tire bald in a very short time. Racing tires do not give any longer life than the touring variety; they are compounded for maximum road grip, and that is not consistent with longwearing characteristics. I would certainly not recommend racing tires for touring use. Most touring-type bikes cannot be leaned far enough, without grounding, to take advantage of a racing tire’s properties, and the racing tire will wear rapidly.
Buy any tire you like. You will get exactly what you pay for, in terms of tread mileage, and all of the available tires give so nearly the same cornering power on a touring machine that the differences would be undetectable.
RIDER-WEIGHT AND PERFORMANCE
A major contribution of your magazine is the test reports of current bikes; they are excellent with one exception. Motorcycle weight is of prime importance in determining performance, especially in lightweights. You supply curb weight, but fail to print the all-important test weight.
The difference between a rider of 140 pounds and one weighing 190 would alter the power to weight ratio 10-15%, equivalent to 2-3 horsepower on the average.
Jim Paterson Detroit, Michigan
We could give test weight (curb weight plus the rider) in our road test reports, but we are not certain it would have any meaning. The primary value of our reports is that they give performance figures that can be compared from make to make, and model to model. To make the results more directly comparable, rider weight is held constant (plus or minus a couple of pounds) for all of the machines tested. Actual performance figures are taken with one of two riders; for machines having an engine displacement under 350cc, the Editor rides — he weighs 162 pounds in leathers, boots and helmet; bikes in the over-350cc class are ridden by yours truly, who weighs 190 pounds, suited-up and ready to go. At one time, l did all performance test riding, but my 190 pounds imposes more of a handicap on the small-displacement bikes than is really fair.
We think that the system now used is quite equitable, and realistic, as riders in general tend to choose motorcycles of a size proportionate to their own. If this is true, and we think it is, then our test results accurately reflect the kind of performance one is likely to encounter in the average hike/rider combination.
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RUN AND BUMP
Recently I have become very interested in motorcycles, and wanting to learn more about the subject I subscribed to your excellent magazine.
There is just one term Î do not understand, and that is a “run-and-bump” start0 Would you please explain this to me?
James E. Derry berry Weston, Massachusetts
International regulations for road racing specify that all of the competitors take their places on the starting grid with engines stopped and then, at the starter's flag-wave, make a push-start to begin the race. With a start of this type, it is essential that the engine fire immediately for the rider will otherwise be left huffing and puffing along beside his machine when everyone else is half-way around for the first lap.
Racing bikes do not start particularly easily, because they have so much compression that it is difficult to make them run-through. If you simply ran with a racing bike and let-fly the clutch, the rear wheel would skid without turning over the engine. Therefore, it is necessary for the
tider to jump on just before releasing the lutch, so that his weight will give the rear tire enough traction to keep it from sliding. Also, the rider’s weight adds to the total inertia, and the bike will roll farther before the engine pulls it to a stop. Of course, if all goes well the engine will start before the bike stops.
The best technique for the run-andbump start is to rock the engine back against compression, and then hold the clutch in and the front brake on while leaning forward against the handlebars. Then, when the starter drops the flag, release the brake and you will be rolling. After the bike is rolling smartly, leap on side-saddle and, just as you hit the seat, drop in the clutch. If the engine fires, as it should, you can accelerate away and begin your race. •
