The Service Department

THE SERVICE DEPARTMENT

STANDARD OR WIDE-RATIO?

I’m interested in the 500 Triumph, hut I'm having a hard time deciding between the Trophy and the Daytona. Most of my riding happens to be on the street, but if I couldn’t go off the road when I wanted to, I'd feel trapped.

I have two pieces of 19 70 Triumph literaIure, one of which (CA T70-B) shows a change in the gear ratios for the T100C and refers to them as "wide.” These ratios have been untampered with for several years, both 500s having had the same gearing. Why have they now made this change? What performance changes can he expected as a result ?

Could you tell me a Jew things about wide-ratio gears such as where and why they are useful, how you know if your hike has them, how they affect riding characteristics, and finally, aside from gear rallos, what good reasons there are for going to the 650 Trophy or Tiger, other than just more cubic inches?

I’ve been riding a 175 Bridgestone for Jour years and it has been a good, reliable machine, but / long for the sound of a Jour-stroke with enough muscle to take me far and wide and still go “over the meadow and through the woods ” occasionally.

Thanks for your comments.

Byars

Northridge, Calif.

As I understand it, all 500 Triumphs brought into this country are fitted with the standard gearbox. In the recent catalog you refer to, an error was made concerning the gear ratios.

Last year, the Triumph Corp. in Baltimore did import a few T100C models with the wide-ratio gearbox especially for enduro riding. The wider ratios permit the rider to plug along at slow speeds in rough country without slipping the clutch, and still enable him to ride at a good clip when road conditions permit.

The standard internal ratios are as follows: 4th, 1.00:1; 3rd, 1.22:1; 2nd, 1.61:1 and 1st, 2.47:1. By comparing them with the optional wide-ratio gears, which haVe the following ratios: 4th,

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1.00:1; 3rd, 1.37:1; 2nd, 1.97:1 and 1st, 3.18:1, we can see that they are, indeed, quite a bit farther apart than the standard ratios. In addition, a close-ratio gearset is also available. The three gearboxes are interchangeable and are available through your Triumph dealer.

Some riders enjoy the extra power a 650 develops, but with the increase in power comes an increase in weight, which makes the 650 harder to control in rough going. 1 suggest that you test ride both machines before making up your mind. The T100C would be happier off the road than the T100R Daytona.

YAMAHAWOBBLE

I own a 1966 Yamaha YDS-3 with about 9000 miles on it. I’m quite happy with it except for three things that I hope you can help me with.

The first is a speed wobble which occurs around 80 mph. Since / rarely ride this fast, it doesn’t really bother me too much, but I’d still like to eliminate it if possible. I’ve balanced and aligned the wheels as well as is possible, but it doesn’t seem to help much. The other

day, while adjusting the chain, I noticed that there is about 1/8 in. of lateral play in the rear wheel and swinging arm. The arm is not flexing, but sliding back and forth on the pivot. Could this be the source of my trouble7 What do you think is wrong, and how can I correct it? (I’ve checked the swinging arm nuts for tightness and they’re okay.)

The second problem is this: lately I’ve noticed that the right exhaust pipe is slowly but surely turning blue around the point where it joins the cylinder. This is an indication, / assume, of overheating caused by a lean mixture or a retarded spark. When I check the plug (B-77HC), the body the round pari around the outside -is a rough, shiny black, the porcelain insulator is a light brown, and the tip of the electrode is grayish white. 'The plug from the other cylinder looks almost exactly the same, yet I’m having no trouble with the other cylinder. And the timing is good. ('The points were changed at 8000 miles and this seems to have no effect one way or the other on the discoloration. )

'The third problem occurs when I’m cruising at about 5000-6000 rpm in the lower three gears. After holding this speed for a minute or two I hear a noise which I can best describe as a rapidly repeating metallic clanking or knocking coming from the engine. I have never

heard this in fourth or fifth gear at any rpm, nor does it occur when accelerating in the lower gears, although / frequently run it up to seven or eight grand before shifting. What is causing this?

Thanks a lot for your help, and keep up the great work on a great magazine.

John Carlson Passaic, N.J.

You proceeded correctly in checking out your wobble by aligning and balancing the wheels, and I am sure that the lateral play in the swinging arm is causing the wobble.

Replacement bushings are available at your Yamaha dealer and are simple to install. After installing new bushings, tighten the swinging arm while the rear wheel is still out and double check for side-to-side movement. There should be just the barest perceptible movement from side to side.

It’s beyond me how your machine managed to get to the 9000-mile mark without discoloring the exhaust pipes, but it is certainly no cause for concern. Practically any internal combustion engine with chrome-plated exhaust pipes will run hot enough out the exhaust port to turn the chrome plating near the port any number of colors ranging from a light, straw-colored yellow to a deep

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purple. If you’re really concerned about the discoloration, there are chemicals available which claim to remove it, but they usually remove some of the chrome plating in the process. The coloration of your spark plugs indicates that the fuel/air mixture is nearly perfect.

Cruising at such high rpm in the lower gears is especially hard on a two-cycle engine and often results in engine seizure. The reason for this phenomenon is that the throttle valve needles are way down in their jets restricting the flow of gasoline It) the engine, while a large amount of air is being drawn in. due to the high rpm. Even though the carburetor design and jetting were worked out very carefully, there still exists a possibility that your engine is running lean under those conditions.

Carbon buildups in the combustion chambers and on the tops of the pistons get very hot as a result of this lean condition, and the airflow over the engine at the lower speeds you would be traveling in the lower gears is insufficient to carry away the heat. Thus, you probably have a pre-ignition or detonation problem. You can cure this by removing the cylinder heads and exhaust pipes, carefully scraping all traces of carbon away from the tops of the pistons, the cylinder heads and the exhaust ports. Also, you would be well advised to shift to a higher gear and open the throttle more to riehen the mixture to preclude possible engine damage.

ONE RICH, ONE LEAN

/ read your magazine and have become very impressed with your Service section. / own a 1961 Matchless 650cc. My problem is with the carburetor (an Amal 389/50). One cylinder seems to be loading with gas and pushing it out the pipe while the other is short on gas. I tuned the bike completely and cleaned the manifold, to no avail. It looks like I’m headed for a new carb. If you have any suggestions first, they would be greatly appreciated.

A. Milano Newton, Mass.

Your Matchless 650 is equipped with an Amal 3(89/50 carburetor as standard equipment, and as such, it is probably not at fault.

Lean running is most often caused by an air leak, either at the junction between the carburetor and the intake manifold, or between the intake manifold and the cylinder heads. Another cause of lean running on one side is

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excessive clearance between the intake valve and the valve guide, either of which may be worn beyond tolerances. Faulty valve seating may be another cause.

1 suggest beginning with the carburetor. Make certain that the clearance between the slide and the body is not excessive. If the slide is loose, replace it. Also check to see that the needle jet is not worn.

Next, it would seem necessary to remove the cylinder heads and check for proper seating of the valves and proper clearance between the valves and the valve guides. Only the barest perceptible side-to-side motion should be present. Replacing the valve guides is usually sufficient, as they wear more rapidly than the valve stems. Be sure to remove all traces of carbon from the combustion chamber and exhaust port with a screwdriver with rounded edges, being extremely careful not to scratch the aluminum. Install new valve springs unless you are certain the old ones are in good shape.

When reinstalling the manifold, make certain that the aluminum flanges are square and that you use new gaskets between the cylinder heads and manifold. Fit new gaskets between the manifold and the carburetor.

Your machine should run as it did when it was new.

A MIND OF ITS OWN?

While riding through the Tehachapi Mountains in Southern California a few months ago, I encountered several stretches of road with deep grooves about an inch apart, sometimes running straight and sometimes wavy. This pavement caused a disconcerting wobble in my front wheel, as if the grooves were grabbing it. / would like to know what is responsible for this instability the road surface or my motorcycle.

My bike is a 1968 BMW R69S with less than 2000 miles on it, and aside from the incident above it is rock-solid, ft is fitted with a 3.50-18 rib tread front tire inflated to 24 psi (manufacturer's recommendation) and a 4.00-18 universal tread rear tire inflated to 21 psi. The day was cool and the road clean and dry.

I. TJ G Daniel F. Whitlock, Jr.

FPO San Francisco, Calif.

I don’t think your motorcycle is to blame. Several sections of road here in

Southern California have been paved in the manner of which you speak as an experiment by the State Highway Department. The concrete itself is of a coarse texture and the grooves are placed in it to aid the runoff of water during rainy spells.

I’m not certain what the state’s findings are on it yet, but, according to tests, traction is somewhat better in almost all instances than with a more conventional road surface. It is more expensive to pave than the normal surface, but it should prove a great safety bonus during wet weather in the mountains. Such a surface won’t be the most comfortable or “assuring” for the motorcyclist, however! (Ö1