The Service Department

THE SERVICE DEPARTMENT

JOHN DUNN

100 for $500?

In the near future (next summer), I plan to build a 100-cc road bike, either from various parts, or by modification of a new bike. The answer needed is to this question: “Would it be cheaper to scratch build or modify?” I have listed below what I hope to have as the end result: Engine, 12-14 bhp, including tune-up kits: frame, stock, Yetman or Van Tech; fork, stock, Ceriani. Telesco; rear suspension, stock Ceriani, Girling; wheels, stock, Akront Alloy 2.50-18 front, 3.00-18 rear; brakes, Honda 160 front, stock rear; tires, Avon; bars, flat drag type; tank, 250-mile range minimum; speed, 65-70 mph cruising, 75 top; weight, 170-190 lb. wet, rear set pegs; instruments, speedometer, ammeter, tachometer, oil temperature gauge; and cost, $500-$550.

I haven’t chosen any one engine yet, but I have narrowed it down to these four: Honda S-90, Yamaha 100 Twin, Hodaka Ace 100 or Bultaco 100.

I had hoped to find one of these engines on a used bike (junk, secondhand, etc.), rebuild if necessary, and modify it if I built from scratch. I weigh 170 lb. and stand 6 ft., 2 in. Would a bike such as I have described be able to handle the hills here in Pennsylvania?

The main reason I have chosen such a small bike is a lack of funds. Small bikes usually entail relatively small costs. They also are comparatively quiet, a most desirable virtue to say the least.

I ask your opinion of my project because I do not want to invest the money just to end up with a bike I cannot ride. I do not want to exceed the $500 price by much. If the cost goes too high, I may as well buy a higher displacement bike for the same money, something I hoped to avoid in the first place.

I have undertaken this project because it would probably be a pleasure to do the work myself. This way, the labor costs will be lower than a dealer-assembled bike.

Charles T. Foley Pittsburgh, Pa.

I think your plan is a bit too ambitious, particularly where the required performance is concerned. The maximum speed of a standard 100-cc sports motorcycle is in the region of 65 mph, with an output of 8 to 10 bhp. It would achieve this speed only under fairly favorable conditions. You would need, depending on the engine chosen, a performance increase of between 25 to 50 percent to maintain a maximum speed of 75 mph. However, with an engine in constant super-tune this could be achieved. To cruise at speeds of between 65 and 70 mph would require the use of almost full throttle. To maintain these speeds up a slight incline or against a moderate headwind, full throttle in high gear, or even possibly in a lower gear, would be necessary. This, in my opinion, is not cruising, for the engine would have to be driven at its maximum potential for 90 percent of its life. To achieve the cruising speeds you require, you would need at least a good, modern 250. Based on your performance requirements alone, I would start shopping for a reasonably priced 250 or 305 that could be reworked to meet many of the other demands, as it would cost a great deal of money and time to maintain the performance requirements you demand of a 100-cc machine.

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TRACKER

I desire to race in short-track events this coming summer, and realize that a special frame will be needed strictly for these events. I know that there are several firms and individuals who offer production or custom-made frames for this purpose. But, as a college student who has put himself through school for four years without any financial help from anyone, and with another year to go, money is a commodity that I am very short on. I find the outlay of funds for one of these frames entirely too much for someone who has to support himself for a year, on what he can earn in three months.

Therefore, I feel that my only alternative is to build my own frame. I have all the facilities here at school free for my use, if I can just come up with a reasonable design, and that’s where the real problem is. I have no experience in frame design and know of no one who could help me. Writing to the manufacturers of these special frames seems fruitless, as many feel that a “nobody” isn’t worth giving advice to, or that giving advice may jeopardize his product, or share of the market.

I am hoping that maybe you could give me the necessary advice and/or plans and diagrams, or tell me who to get in touch with to get the necessary material to build a competitive shorttracker frame. Any information you can send me on wheelbase, steering head and down-tube angles, rear arm length, ground clearence, and any other pertinent information will be much appreciated. As a reference, I shall be using a 1966 Bultaco 250-cc engine.

Darby E. Ryan 807 W. Freeman Carbondale, IT 62901

Flat track racing has become a very specialized sport with respect to frame design and component selection, because of recent lack of restrictions governing machine specifications. Apparently, design specifications are open, providing they meet required safety and class regulations. However, before starting, I suggest that you contact the AMA for a full set of rules governing this type of racing.

I also suggest that you start off by building a simple frame and leave the “trickery” that is employed by some builders to a later date. You will learn a lot in one season of racing just by being involved. The frame will have to be light, but strong, and will not require rear suspension. Base your design on a triangulated structure that will ensure adequate torsional and lateral rigidity. Start with a wheelbase of 54 in. and leave provision in the design for an adjustment of 2 in. either way. Position the engine to obtain a weight distribution of 50-50 on front and rear wheels. Try to keep the center of gravity as low as possible, bearing in mind clearance problems when cornering at acute angles.A 25-degree steering head angle will provide a fairly good compromise at this time. I think the above parameters will provide a good basis for a simple design. However, if any reader has been through a similar project, I am sure that Darby would be pleased to hear from him.

'OLING AND OILING

I can’t figure out what “ear ’oling” is. I’ve seen it mentioned in your August, ’65 road test of the Ducati Mark III, and on page 24 of your November, ’68 Service Department. Please tell me what this is.

Also, is oil injection pump failure or malfunction a common occurrence on Japanese two-stroke bikes?

Finally, what is the average gasoline mileage of Japanese 350s such as the Yamaha Grand Prix, Kawasaki Avenger, and the Bridgestone 350 GTR? I get the impression that it’s not exceptional from your road test of the Kawasaki A 7 (CW, June ’6 7).

Geoffrey Dearth DeForest, Wis.

The expression “ear ’oling” is British road racing terminology. A person’s ear is referred to as an ear hole (slang) or, as pronounced by the London cockney, “ear ’ole.” A rider that is really “ear ’oling” is one that appears to be going extremely fast and is presumably getting his ear ’ole very close to the ground when cornering. There are many other expressions related to the act of going quickly on a motorcycle that, when explained, do sound a little bit silly.

Most of the oil injection systems used on Japanese two-strokes are well-designed and engineered. However, I believe that a lof of the troubles that are experienced result from maladjustment caused by lack of knowledge on the part of the persons responsible for service.

Yes, the 350-cc two-strokes referred to, do tend to be a bit thirsty. The average fuel consumption when ridden relatively hard is approximately 40 mpg. Remember that all these machines do produce a lot of power even when compared with some larger displacement machines. If you turn on the power they will definitely soak up the gasoline. However, if they are driven reasonably, the fuel consumption can be improved considerably.

SMART KNOCK

Lately I’ve had trouble with idle mixture adjustments on my Twin A mal 930 concentric carburetors, so I decided to dismantle and clean them. While doing so I noticed the bronze sleeves above the jets were of unequal height in each venturi. One of the sleeves was fairly loose, too. Could this be my problem, and, if so, how high should the sleeves be?

Also, my 1968 Triumph Bonneville has been kicking out of fourth gear. I tried hooking my foot under the gear change lever to hold it in gear, but all I got was a smart knock on my toe when it kicked out again. I have this problem with fourth gear only.

John A. Dunn Lancaster, S.C.

The bronze sleeves to which you refer should be of equal height, and also be a snug fit in the carburetor. The fact that your machine is jumping out of fourth gear indicates that the gear is not being fully selected or that the engaging dogs are badly worn. I suggest that you have this problem rectified at the earliest possible time before serious gearbox damage occurs. It will not only prove expensive, but it is highly dangerous to encounter a gearbox lockup when traveling at even moderate speeds. If an engine seizes, you can quickly whip in the clutch, but if the gearbox locks, there is no way of freeing the rear wheel.