The Service Department

THE SERVICE DEPARTMENT

GORDON H. JENNINGS

MATCHMAKERS?

I am in the market for a good road machine that is reasonably light (not as heavy as the Harley 74 OHV) with a lot of power if needed (650 to 750cc’s), and I would greatly appreciate it if you could help me.

I have gone to dealers, and of course what they sell is always the best.

As an engineer, I get a little more technical, probably, than the average man.

Before 1 buy I would like to get a bike with a good clutch, good riding traits, good resale value, and something that 1 can get parts for (if needed).

1 am considering the following cycles:

1. Triumph Bonneville

2. BSA Super Rocket

3. BMW R69s

4. Norton Atlas

5. Matchless 750cc or Apache

6. Royal Enfield Interceptor or Constellation.

Now I am broad minded and would never darn anybody for helping me select, nor would I go to a dealer and tell him that Cycle World said that his machine was not as good as X Brand. In view of this, please help me pick a good, hot, nice-handling road machine. C. Bowen Hartford, Conn.

One of the things we never do is make specific recommendations on the choice of a motorcycle. To do so would be as unwise as recommending a wife — there is too much personal taste involved in both cases to allow anyone but the party directly concerned to make the selection.

You ask for “a good, hot, nice-handling road machine.” All of the motorcycles you list fit that description; you will just have to try them all and, for better or worse, make a decision. Our road tests can be of help, as they list features, performance, and any weaknesses that come to light during the test period. Requests for back issues containing the road tests of the bikes that interest you may be obtained by writing to our circulation department.

MULTI GRADE OILS

Enclosed find my check for a subscription for one year to your magazine. At last l found an American magazine that fulfills my requirements; keep up the good work. Your magazine is very widely read here by all the people of the sport. Many of them ask me to translate for them even the most insignificant ads, but even these who cannot speak English can understand your very informative road tests.

I have a certain question. I own and race with some success a Honda CB 92 and have a dilemma. The manual recommends to use S.A.E. 30. I use Castrol S.A.E. 30, but realizing the advantages of a multi grade oil, I ask if I wouldn’t have any problem by using Mobiloil 10-30, for touring and racing. I haven’t used yet this particular brand because some people think that multi grade oil is bad for engines that turns so many rpm. I also want to ask if for racing I could use Castrol R. 40? I want to know your opinion about all this. Even though the races here are. rather short, they are very hard on the machines. Leonel Gomez Santa Ana, El Salvador, Central America

Multi grade oils have been given a lot of publicity in recent years, and they are of some usefulness in meeting the year-in, year-out oil viscosity requirements of the modern automobile. However, the motorcycle is something else again.

Generally speaking, the motorcycle engine will be stressed much more heavily, and there is some evidence that multi grade oils may not give the kind of lubrication that is needed under high loadings. There may very well be circumstances that would call for such oils but, by and large, one should not try to “second guess” the engineers who specified the oil for your motorcycle. Sometimes, racing conditions will require the next heavier grade of oil or cold weather one grade lighter, but I would not go beyond those limits. Castrol R 40 would be very good for racing.

CYLINDER SIZE

My friends and I appreciate the fine job

you are doing in producing a top-notch cycle mag. Some of us were discussing the M. V. Agusta and the revving ability of such an engine. My friend claims that such an engine is able to rev considerably higher than an engine of fewer cylinders and equal capacity.

And how would horsepower and torque figure into the picture? Specifically, what were the horsepower and rpm on this engine and what would be the theoretical rev limit of this engine.

Incidentally, 1 am curious about your excluding torque figures from your road tests; you must have a good reason; why? Mike Madden Alexandria, Virginia

Your friend is essentially correct: for any given displacement, the engine having many cylinders will be able to rev higher. The reason is simply that a small piston, moving through a short stroke, can run through its cycles faster than a big piston, traveling over a long stroke. Hence, a 500cc engine having 4 small cylinders will turn faster than a 500cc single.

Oddly enough, there will be little difference in torque between the four and the single, and the difference in power will depend to a large extent on the operating speed. The rev limit for the MV was, as I recall, rather near 10,000 rpm and although no power figures were released by the makers, it must have had about 70 bhp.

The theoretical limitations for this and other engines are far too complicated for a discussion here, but they will be covered in an article that will appear in CW soon.

We do not include torque figures in

our road tests because so few manufacturers make the information available.

SPARK PLUGS

I’ve had a little problem with my Harley-Davidson H model scooter. 1 think that Autolite spark plugs are the best made and have been using them in my scooter even though the Harley-Davidson people say their plug should be used. 1 broke the engine in with an A5X, which is a small engine plug with a medium heat range. After that 1 ran it about 150 miles at 25 mile intervals at close to top speed and the engine heated up. After that, I switched to a colder plug anti now the engine is running perfectly. Do you think 1 damaged the engine by using too hot a plug? Guy Trotter Charlotte, N.C.

Without actually dismantling your engine and inspecting the parts, there is no way of saying, for certain, that damage was done. However, overheating — and particularly the kind of overheating you were getting — is always very bad. A toohot plug, which you were apparently using, can cause pre-ignition, and that will result in much of the heat from combustion being forced into the piston crown and cylinder walls. Such overheating, even when it does not produce an immediate engine failure, can be the cause of muchshortened engine life.

All things considered, and I think you will agree with me in this, you would have been wiser to have followed the manufacturer’s recommendations in your selection of spark plugs. There is certainly nothing wrong with Autolite plugs; on the contrary, they have been used with great success in every kind of engine imaginable. Others too, will do the job (my personal preference is for the NGK spark plug); the trick is in getting a plug of the proper heat range. There are, of course, things to look for when “reading” a plug to determine if it is of the proper heat range, and if the mixture is right. We will try to cover the entire spark plug picture in the very near future.

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DISC BRAKES, PRO AND CON

7 read your article in the May issue on disc brakes for cycles. I was talking to a karting fan who said that when disc brakes got dirty or oily they were practically useless. Wouldn’t this be quite a problem on a cycle; especially if one surface is on the inside of the hub as on the Pointer? Philip Van Valkenburg Cambridge, Wis.

No as a matter of fact, experience has shown that the surface which presents no service problem is the one that is shrouded. The exposed surface picks up some road grit, and pad wear on that side is much heavier than the one on the inside. However, even the wear on the exposed side is not heavy enough to suffer in comparison with drum-type brakes.

Furthermore, to the best of our knowledge, the better disc brakes on karts have never had any dirt or oil problems. When the brake is applied, the leading edge of the friction pad wipes away dust, water or oil and the brake functions normally. Indeed, the high contact pressure of the friction pad is usually enough to push right through even a fairly heavy coating of oil and, of course, water is no problem at all. Disc brakes have their faults — chiefly the need for relatively high actuation pressures — but sensitivity to dust, water or oil is not one of them.