The Service Department

THE SERVICE DEPARTMENT

GORDON H. JENNINGS

BONNEVILLE CLASSES

I read in a certain automotive magazine an advertisement for Triumph Motorcycles that they hold the record for standard production gasoline Class-C motorcycles at 147.42.

You claim to have raised the record in PS-C from 127.77 mph to 135.74. Please explain.

Also, what happened to Benny Holton?

Howard L. Michels

Livermore, California

Actually, we raised the record in our class to 137.075 mph. You apparently missed the end of the story, which was easy to do, due to a goof on our part in laying out the magazine. Our fastest qualifying run was 135.74 mph, but we went a bit faster the next morning when running for record. The first run, in still air, was just over 140 mph; the return was made into a wind that came up, and the average of the two runs was 137.075 mph — the record for 40-inch PS-C (Partial Streamlined, Class-C) bikes.

Triumph also holds the record in the 40-inch, Class-C unstreamlined category. And, it is indeed, at 147.42 mph. This may seem an anomaly, considering that our partially streamlined bike was 10 mph slow with (it says here in the fine print) the same engine. This apparent contradiction is explained by the AMA rules governing Class-C competitions.

The AMA Manual says that a Class-C motorcycle is one made for general use on the street, with no more than two cylinders, and two valves per cylinder, or more than one overhead camshaft. The 500cc overhead valve and 750cc side valve machines are limited to 4-speed transmissions. The smaller, 250cc bikes may have a maximum of 5-speeds. Gasoline fuel is specified. Beyond these rules (with a few additional applying to different types of events) the tuner is permitted almost anything. Special cams and oversize valves are legal, and we had these items in our Bonneville entry. Racing carburetors are also permitted, as are special crankshafts, rods, pistons and a whole gaggle of miscellaneous parts. It is common practice to modify the cylinder head practically beyond recognition. Modifications to the frame are allowed as long as the tuner does not depart from the “same basic design and material as made by the manufacturer,” whatever that means.

One would think that all of this offered unlimited latitude, and in most cases it does, but the rules are so indefinitely worded, so ambiguous, that one cannot be certain whether the AMA wants the machine to appear at the track in completely stock tune, or if they will extend their blessing to a machine in which only bore and stroke meet original specifications. In practice, the whole matter is subject to the whims of the AMA official at each event, and what is legal one week may be rejected the next. The situation is always infuriating.

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In our case, we are proceeding slowly with modifications, staying fairly near stock condition so as to avoid any question about the machine being “legal.” This will be a handicap, compared with other motorcycles in Class-C, but we want to stay away from frame modifications, etc., that would make the bike unsuitable for “street” running.

Now for your last question. Nothing happened to Benny Holton except that he couldn’t get his bike going fast enough in the time available. He did qualify to make an attempt on the record we had just established, but his best run of 138.67 mph was done with the aid of a fairly brisk tail-wind, and he knew that there was no chance of getting a two-way average high enough to get the record. Accordingly, he elected not to spend the $20 fee required by the AMA for record attempts. We understand that he will be back next year to shoot at our record again. We will be there to push the record up a bit higher. It should be an interesting week.

DETERGENT OILS

I've heard a lot of pro’s and con’s on the use of detergent oils for breaking in a new motorcycle. Shortly l will be riding a new BMW R-60 and 1 want to use the proper oil for breaking it in.

Any advice you can give me will be greatly appreciated.

Ralph W. Lemnah

FPO San Francisco, California

Detergent oils seem to worry a lot of people, for what reason I cannot guess. Except for racing engines, which have very high loadings and demand the ultimate in lubrication, detergent oils are best. The detergent chemicals may dilute the oil slightly, and cause a fractional loss of borderline lubricating properties (which is the reason for not using a detergent oil in racing engines) but they also prevent the build-up of piston varnish and general carbon deposits. An engine using detergent oil will always be cleaner, internally, and will not suffer problems with sticking rings and valves. Also, most of the detergent oils contain additional compounds to counter acid contamination of the oil. These acids are created in the combustion process, and are strong enough to actually “etch” metal from the cylinder walls. Most of the acids are pushed out of the engine, in vapor form, once the engine is warm, but when cold, the acids condense inside the engine and contaminate the oil. Frequent oil changes are one way of dealing with the contamination; additive oil is a better way.

I would definitely recommend detergent oil for a new motorcycle, unless the maker specifically warns against it. Also, for new machines, a little “upper end” lubricant, added to the fuel, will help in polishing off high-spots without scuffing, which is always a problem in new. tight engines.

Where an older motorcycle, one that has run a lot of miles on a non-detergent oil, is concerned, I would be reluctant to recommend a change to a detergent. Usually, these old engines will have built up a lot of varnish, carbon and gum, and the detergent flushes all of this mess out of the corners and sends it into the engine’s bearings in large chunks. In a new engine, or any engine that is clean inside, the detergent oil picks up the carbon and gum, as it is formed, and holds it in suspension as minute particles, until the oil is drained and renewed — which removes the carbon from the engine.

In connection with this matter of detergent/non-detergent oil, I should mention that even though many people are not aware of the fact, there are detergent oils for two-strokes. Saab (the Swedish automobile company) markets a six-pack of canned oil for their two-stroke engine, and this oil has a detergent, to prevent deposit build-up in the transfer and exhaust ports. Also, in the Saab oil, there is a chemical blender that makes it mix more easily with gasoline. This oil, available in the eastern states, would be just the thing for normal touring use. For racing, the special castor-based oils made for that purpose are hard to beat.

Incidentally, it should be understood that the requirements for racing and for touring are completely different. A good racing oil is one that provides good lubrication under conditions of extreme heat and pressure, even if it has a tendency to form heavy gumsand carbon deposits — as is true of virtually all castor-based oils. Of course, this is not really a disadvantage in a racing engine; frequent overhauls are necessary in any case and any deposits can be removed before they become bothersome.

A good touring oil must meet requirements that are actually more difficult. The average rider does not wait until his engine’s oil supply is warm before setting off, and he does not change to a heavier oil before indulging in a little flat-out running. Thus, a touring oil should be thin, for good circulation when cold; and heavy, to provide adequate lubrication when hot. For this reason, most automobile and a couple of motorcycle manufacturers now specify a multi-grade oil. There are other factors involved, too, and we shall try to wind the whole matter up in a single article about oils in some nearfuture issue.

SPECIAL GEARING

I have aspirations of being an amateur builder and would like to know what I could do about getting a gearbox of at least four speeds; preferably without having to get an engine along with it. From what 1 read in CW the trend today is toward unit construction, with the gears enclosed in a housing which also surrounds the engine.

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Is it possible to de-unitize the gears and put them in a separate housing, and if this is done, is there any place to get the gears? Also, are there any separate gearboxes in existence and available used or otherwise?

Michael Barash New, York, New York

All things are possible, if you are willing to spend enough time and/or money. Almost any gear set could be removed from its original casing and installed in another, special case made for the particular job. In fact, it is not all that difficult to make a case out of welded-together, machined aluminum plates for most gear sets. That would enable you to adapt any gear set to any engine.

As for suitable gears, there is really quite a variety. The Yamaha YDS 2 has a five-speed transmission, and so does the latest H-D Sprint road racer. The latter machine has better ratios for racing; the Yamaha gears are essentially for touring.

In the big displacement class, closeratio gears, in separate cases, abound. Albion transmissions can be fitted with about ten different gear sets, with close and wide ratios. The BSA Gold Star transmission is available with three different gear sets, one of them ultra-close ratio for road racing, and there are special fivespeed racing gear sets for the big Norton. Triumph, too, has special transmission gears available.

Local dealers will usually not have much, if any, information about special gears; it is usually necessary to contact the importers, direct, and sometimes only a letter directly to the appropriate factory will yield results.

MORE HONDA HOP-UP

In the August issue of CYCLE WORLD, Mr. W. B. Swim reports that “Honda officially announced their 90cc model. The new 90cc model will have a bore and stroke of 49mm x 46mm.”

Is it possible to bore out a “50” barrel to these sizes?

Gene A. Rusnak Miami, Florida

We understand that it has become fairly common practice to overbore the Honda “50” to take the 125’s 44mm piston. However, it would be stretching things a bit to go out to 49mm. That would be a .354in. overbore, and that is a bit too much.

Incidentally, owners of the Honda 50 should be made aware that it is not possible to change over to the cylinder and piston from the new Honda “90.” The new Honda is all new, with a completely different cylinder and head, and crankcase. The crankshaft has a longer stroke, and is sturdier and carried in larger bearings. Given sufficient machine-shop reworking, it might be possible to make things fit, but the cost would be so high that it would be less expensive to simply sell the “50” and buy the new “90.” •