The Service Department
THE SERVICE DEPARTMENT
GORDON H. JENNINGS
WHY, OH WHY?
I have two questions which I wish you could answer. One: why isn't the Manx Norton 500 approved by the AMA for Class C competition? Two: the AMA rules state that the Class C 45-cubic inch class shall be composed of approved machines of not over 750cc for flathead engines and 500cc for overhead valve engines. Is there really 250cc difference in potential between overhead valve and flathead engines? It seems to me that any racing engine which is half again bigger than its competitors has a decided advantage.
Glenn H. Crum Iowa City, Iowa It should be obvious that the reason for the AM A's refusal to approve the Manx Norton is based on the fact that it is an out-and-out racing machine, and only mass-produced touring bikes are allowed to compete under the Class C rules. The Harley-Davidson 45-flathead, on the other hand, is a mass-produced model, and can be purchased at any Harley-Davidson dealer for purposes of riding back and forth to the office. Unfortunately, most dealers are temporarily out of these bikes, and through some regrettable oversight, they are not listed in the company's sales brochure, but I am certain that the matter will be put right. To think otherwise would be to accuse the AMA of gross bias.
To take care of your closing questions: yes, there is really 250cc difference in potential between the overhead valve and flathead engines; not in every instance at this point, but the flathead, as currently built by Harley-Davidson, is at the zenith of its development, whereas the overhead valve engine's upper limit is not yet in sight. Given enough time, the overheads will begin to consistently defeat the flatheads, but for the moment, they are quite evenly matched. It was in the interest of close competition that the AMA's rules were originally developed, and you have to admit that, to that extent, they have been a success. Or, would you prefer that all bikes run under the same displacement rule, which would effectively eliminate Harley-Davidson from racing, where they are now contributing a lot of spectator appeal with their big, noisy and fast machines? That "half-again-as-much" displacement is a decided advantage, as you said, but we would not be seeing those bikes at all, otherwise.
TURN RIGHT; FALL LEFT
We have noticed, in riding motorcycles and scooters, that steering may be accomplished by turning the handlebars in the direction opposite that in which one desires to turn. We wonder if you could tell us what causes this? Some of us claim that the gyroscopic action is responsible for tipping the bike; others think that the wheel follows a course in the direction steered for a short time while the upper part of the bike and rider stay more or less stationary, thus tipping the bike for the desired direction of turn.
Frank B. Kotier
Lexington, Mass.
What the "others" think is probably correct. Although gyroscopic precession forces would tend to produce the same effect, the forces are just not of a high enough order to account for the extreme quickness with which a bike will drop over into a corner when the handlebars are given a quick twitch the wrong-way. The only thing that holds a bike upright is the manner in which the wheels are constantly steered under the bike's center of gravity. Gyroscopic effect works for us at speed, but not when just plugging along slowly. Then, it is a balancing routine, pure and simple, with the rider moving the tires to keep the bike from falling. Thus, when this balance is deliberately upset, as by the wrong-way twitch of the bars, the bike leans down in a snappy fashion indeed. This is, incidentally, a very useful competition riding technique. Nothing else will help a rider down through a series of fast S-bends in quite the same way, and speedway riders employ it with great success in getting set up for turns on the dirt ovals.
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NOT GUILTY
After reading the test of the Triumph Bonneville TT Special I can't help wondering if you have stock in Johnson Motors or a brother-in-law named John-
son.
How can you have a comparative road test if you use a "souped all to hell" model that the average guy could not do in 30 years? We can supply you with a Norton Atlas with "parts generally available" that will make the stock Atlas with 7.6:1 compression appear to be parked.
Further, Mr. Jennings is way out on his answer to putting 9:1 pistons in the Atlas. This is old stuff in the Atlas and I am informed that Webco is going to deal in 10.5:1 pistons for the Atlas. How the Triumph will run on 12:1 and the Atlas will blow on 9:1 is something 1 would like explained?
Yours for "equal chance" road tests. Are you testing road machines or not?
G. Stable
DeLuxe Motorcycle Sales
St. Clair Shores, Mich.
No, as a matter of fact we have neither stock nor relatives in Johnson Motors, although to be quite candid, I must say that for myself there is a desire that such was the case. They are a going concern, and either of those connections might be of some benefit.
Getting on to your questions: we do not, except in very rare instances, test motorcycles that have been, as you say, "souped all to hell," and the Bonneville TT Special was not one of those instances. Part of the report was given to a discussion of the very special engines used in their record-breaking streamliner, because we thought that the readership might be interested. None of these special parts were used in the TT Special, as the report clearly stated. It is a motorcycle in which everything but the exhaust system (mufflers are standard) is installed by the factory. The TT Special differs from the standard Bonneville only in its compression ratio and carburetion, and in the fact that it is not delivered with lighting equipment. The installation of racing megaphones was all that was done to our test machine. Anyone with the required $1158 can buy one of these bikes. The reception has been so good that the factory is now producing them in quantity and they will be available throughout the country. And, the man who owns a standard Bonneville can convert to TT specifications by changing pistons and carburetors; it won't take 30 years but more like 30 hours, or less.
As for your final complaint, that I said the Atlas would "blow" if equipped with 9:1 pistons, I simply never said anything of the kind. The reader's question concerned the Atlas; my answer was directed at all motorcycle engines — even the Triumph. My original statement stands: high compression ratios carry with them many problems, not the least of which is a very high thermal loading on the engine, and when the loading to too high, the pistons will fail, or the valves. Engine roughness I also mentioned, and that answer also stands. High compression ratios are one of the direct roads to high power outputs; they also tend to shorten engine life and in the interest of reliability most motorcycles are delivered with a compression ratio a good bit lower than the one that would represent the absolute limit. The Atlas equipped with high-compression pistons is going to be faster than with the stock compression ratio, and it won't collapse under the first burst of full-throttle, but it would be unreasonable to expect that the modified machine would not lose some reliability.
HARLEY-DAVIDSON POWER RATINGS
In your October issue, you said that Harley-Davidson claims 55 horsepower for the XLCH. Enclosed is the information page from a booklet I received from H arley-Davidson. You will note that the horsepower claim is 47 for the XLCH Sportster.
Philip Van Valkenburg
Cambridge, Wisconsin
There appears to have been some confusion in those XLCH power ratings. However, we have (in addition to the data sheet you sent) the latest brochure from Harley-Davidson and it lists the XLCH Sportster as having 47 horsepower. So, as we mentioned in the road test, the XLCH engine does develop 47 horsepower, and mighty stout, honest horses they are, too.
