The Service Department

THE SERVICE DEPARTMENT

GORDON H. JENNINGS

HONDA CAMS

Consider my wrists thoroughly slapped for saying in this column in the April issue that I knew of no firm making cams for Hondas; I of course missed mentioning the firm of Harman & Collins, one of our advertisers and an old firm with an excellent reputation.

Forgive me gentlemen, and you Honda riding readers as well.

SPEED WOBBLE

I own a 1957 Triumph T-110. Your article "Frames and Suspensions” prompts me to ask you for some advice.

My problem is this: I believe 1 am the owner of one of these machines with steering inertia trouble, and have already experienced a stay in the hospital because of it. I have my machine stripped and would like to know where I can have the frame checked for alignment and straightened if necessary.

Also, would it help me to put on a hydraulic steering damper like the one on the Honda CL-72 scrambler or BMW R69S? Which would be the most practical and easiest to put on?

My speed was about 65 mph when the forks started shaking. The road was paved and very smooth. This sort of thing had happened about 3 times before at the same speed, but to a much lesser degree and stopping of its own accord after a few seconds.

Ismael L. Carrasco Balmorhea, Texas

It seems most unlikely that a frame misalignment could be the source of your problem. Such a misalignment might make the bike handle a bit peculiarly, but there is nothing in that direction to create a speed wobble — unless, of course, the steering head was bent enough to radically change the fork angle, and that does not appear at all probable.

There is a much better chance that the steering head bearings had become worn, or worked loose, and that could definitely cause a speed wobble. Careful re-building and reassembly would cure that ailment. Unless your Triumph has been modified, by a change in wheel diameter or by the fitting of an “odd-ball” tire, any simple rebuild should be all that would be required. The stock Triumph had no such problem.

If you are feeling a bit doubtful about the machine — and you might well be after having been tossed on your head — a hydraulic steering damper would do wonders for your mental situation; and it certainly wouldn’t hurt the bike’s handling. Either of the steering dampers you mention would he fine; I suggest buying the Honda part just because it would probably be less expensive. You can vary the damping action by changing the distance between the steering head centerline and the fork-end of the damper. This will change the damper stroke, relative to the amount of steering movement, and thereby alter the damper’s effectiveness. To get the right stroke, it might be wise to connect the damper to the forks by means of an arm that is adjustable for length. This need not be a particularly tidy bit of hardware; after determining the proper length for the arm, a permanent part, without an adjustment, can be made and installed.

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I cannot suggest anyone to carry out the repairs and/or modifications you have in mind; I am totally unfamiliar with the shops in your area. However, you will find listed in our dealer directory (in the back pages of any issue of CYCLE WORLD) a whole flock of Texas motorcycle dealers.

LIGHT-WEIGHT PISTONS

Explain to me briefly the advantages and disadvantages of light-weight pistons. Also, can the crankshaft ever be responsible for limited rpm, while the pistons and valves aren’t?

Larry Spangler

APÖ 39, New York, N .Y.

Basically, the advantage of light pistons is that they make life much easier for connecting rods, crankshafts and bearings. With every stroke, twice per revolution, the piston must be accelerated from rest to whatever speed it reaches, and then braked to a halt, and the force required to do this accelerating and braking puts heavy loads on the components just listed, and on certain parts of the piston itself. As piston weight rises, so does the load, and that is why virtually all pistons are made of light aluminum — a material that is unsuited to the requirements in every other way. The only disadvantage of lightweight pistons is that if the lightness is carried too far, the piston may not be strong enough.

The only limit imposed on engine speed by a crankshaft would be the point at which the shaft either bent or broke; apart from that structural aspect, the crankshaft can have no effect on engine speed. I suppose it would be possible to build a crankshaft with such large bearing areas that friction would limit the operating speed; such a thing would, however, be out of the question within the normal range of bearing sizes.

AVGAS

Would you give your opinion on the possible advantages or dangers of using aviation gasolines in motorcycle engine. 1 am especially interested in their use in high-compression two-strokes to reduce plug fouling and the formation of deposits in the combustion chamber.

Bruce Sturkie

Stillwater, Oklahoma

When you say “aviation gasolines,” you take in more distilled petroleum products than I care to discuss as a single subject. However, I assume that you mean, generally, the stuff they pour into small private aircraft.

That being the case, it wouldn’t have much effect one way or the other. If the octane requirements of your engine are satisfied by ordinary service-station type gasoline, then there would be no advantage in using the more exotic fuels. Your engine would run no cleaner and'develop no more power. Obviously, if you raised the engine’s compression ratio, to take advantage of the higher octane-rated avgas, then somewhat better torque and power could be expected, but there is some danger that the engine would not remain healthy when subjected to the higher thermal and gas-pressure loadings. Broadly speaking, if you want to convert to an exotic fuel, alcohol would be much better than avgas, as it can be used with very high compression ratios and has a high heat of evaporation, which would help to cool the engine. And, alcohol tends to be fairly clean burning which would minimize those combustion chamber deposits. •