The Service Department
THE SERVICE DEPARTMENT
GARY BRAY
THRILL OF SPEED
I have always envied the thrill of speed and I hope to enter the quarter-mile drags next year. To do this I want to modify my machine, but still keep it on the road.
I have a 1960 BSA 650cc Super Rocket. The crankshaft has been lathed down to 1 5/8" (flywheel width) and I am going to have the system balanced as soon as my parts arrive. I have decided to put high compression pistons and a 357 camshaft in the machine. Could you please recommend a compression ratio which would be high enough for racing but not too high for the road? (10:1 or thereabouts.)
My biggest problem at the moment is adapting my single carburetor manifold to a dual carburetor piece. I was given some distance specification for mounting carburetors. 1 was told that the carbs should be ten inches from the tip of the spark plug to the main jet and the pipes should be 50" from head to tail.
1 would appreciate your help in this matter very much if you might verify these specifications or inform me of a more suitable change. I also contemplate a blown out extension pipe design between the inlet valves and the carburetors to help the mixing process before the gases reach the valve, but mechanics say this only works with some motorcycles.
John McLeod Woodbridge, Ont., Canada
The choice of the 357 camshaft is as good as any for the uses that you intend for your machine. A compression ratio of 10:1 or 10.5:1 should produce the desired results, yet create no side effects when the machine is ridden on the street.
It seems that an induction system which measures IVi" from inlet valve to the carburetor spray bar is the ideal length. Total exhaust pipe length with the 357 cam and this length inlet port should be 39Vi inches.
A 50-inch exhaust system is too long; performance will suffer. In shaping the ports I would suggest retaining a straight type design or one that becomes slightly smaller as it progresses inward toward the valve, and then outward just before the valve guide is encountered.
The port design you have contemplated may not produce near the desired effect of the two more standard port types. Porting should be attempted slowly and carefully; remember, once material has been removed, it's quite hard to put back.
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SOME MODIFICATIONS
I own a 1965 500cc Triumph and am thinking of modifying it, but there are some things 1 need your help on. Could you tell me if there is enough material on the cylinder walls to bore it out to the 650cc size? If there is, can I use the M-C 650cc IOV2-I pistons with my rods and wrist pins, without throwing the engine way out of balance?
Iskenderian makes a cam for my bike with a lift of .380; will this clear the IOV2-I pistons?They say to use stronger valve springs, either S&W or Terry; what companies are these, and how can I get in touch with them?
Tim Tythcott
FPO, New York, N.Y.
Your 500cc Triumph cannot be overbored to accept 650 pistons. There just isn't enough material in the cylinder. It is almost a certainty that the valve pockets in the pistons will have to be relieved if a camshaft with as much lift as you contemplate using is installed. By placing a layer of modeling clay in the valve pockets and rotating the engine carefully (after partial assembly), it can be determined if any mill work at the valve pockets is necessary.
A clay impression left by the valve should be at least .035 thick. I realize assembly and disassembly of an engine is time consuming; however, it is most important for best results in speed and reliability. It's cheaper, too, than replacing a perfectly good part that became broken or bent because time wasn't taken to insure freedom of operation.
Contrary to what many people believe, replacement parts designed to increase power and performance don't always slip right in. Some alteration in other engine components is usually needed at one point or another. An area frequently overlooked when a high lift camshaft has been installed is whether the valve spring collar will operate without interfering with the valve guide. Your Triumph will probably need at least .125 removed from the guide for adequate clearance.
The S&W valve spring is distributed by Webco Inc., 218 Main Street, Venice, Calif. However, both the S&W and Terry valve springs should be available through most authorized motorcycle dealers.
DON'T LIKE PUSHING
I have a problem with the ratchet mechanism on my Matchless. The problem is with the dog, the part that engages on the downstroke and ratchets when the lever is released. I have gone through three of them in the five weeks I've had the machine. The first time 1 had the old part built up and hard-faced, as one shop suggested. The last one was a Norton part, put in by a shop with an excellent reputation. It is a 1963 machine, has been bored and stroked to 620cc as well as some other goodies, if that has any bearing on the problem.
Tom Enright Santa Rosa, Calif.
Kick starter failure, while not a source of annoyment on other machines in which this type of gearbox was used, did pose a problem when fitted to the 600cc Matchless Typhoon. The difficulty, it would seem, is in design of the starter mechanism. It just isn't strong enough to handle a large displacement single, especially a temperamental one that kicks back every time you look at it the wrong way.
It has been claimed that much of the wear received by the ratchet pawl was the result of too weak a kick starter return spring. Insufficient pressure against the starter assembly would allow the ratchet to engage when the motorcycle was in use. A stronger replacement spring is available and certainly worth a try.
Assuming there is some engine kickback, it won't do the starter pawl much good. Especially when you consider the energy developed by the powerplant's insides is traveling in the wrong direction while, say, 150 lbs. + is standing on the starter pedal. Should a kickback problem exist, an attempt to minimize this condition, either through closer attention to ignition timing or some experimentation with the spark control lever, may greatly reduce the kick starter failure you have been experiencing.
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TIRED OF GOING SLOW
I have had my Cushman motorscooter for about two years now and I am getting tired of going slow. I'm wondering if there is any way at all I can speed it up 10 or 20 mph without boring it? If so, how much would it cost and would it be safe for the engine?
Jim Dunn Lame sa, Texas
The financial investment involved in increasing the performance of your Cushman would, I am afraid, greatly outweigh whatever speed there is to he gained by such a venture. Since the Cushman powerplant was not intended for other than cheap, dependable transportation, it does not take readily to hopping-up.
This does not mean the engine itself isn't strong enough, but rather that the design is too limited. The basic area in which this engine suffers the most is its breathing characteristics. Naturally, a more efficient camshaft would be the answer, or so it would seem. This doesn't solve much, however, for a high performance camshaft is wasted without increasing the valve area, induction and exhaust systems. You see, one change leads to another. This in turn means a greater outlay of money. More often than not, what is gained in speed must be considered insignificant.
There are other aspects to this problem. Basic experience and understanding of the internal combustion engine can be acquired by working on one's own machine. If you choose to attempt a power increase, I would suggest getting a cony of P.E. Irving's "Tuning for Speed," Fourth Edition; a motorcycle dealer in your area should be able to get it for you.
One last point should be mentioned, I feel. That is the relation of your Cushman, and its proposed speed increase, to the aspect of safety. Will more speed mean less stability? What about brake efficiency? One final question: would it not seem better to progress to a motorcycle where braking, handling and speed are more closely bound together?
NO TEETH
/ have a hot 200cc Triumph Cub which 1 can't keep the transmission in. The layshaft and pinion gears keep stripping. 1 have replaced six sets already. Is there a heavier gear to replace them? If not, what can be done to remedy it? 1 also have friends with the same trouble.
Sam Wilson San Pablo, Calif.
A heavier gear set is not available for the 200cc Triumph. The Cub transmission is fairly trouble-free, even in competition. Extreme abuse in one form or another causes the greatest amount of gearbox failure. Chronic shedding of gear teeth, however, suggests an underlying cause which has been overlooked.
A contributing factor to repeated gear breakage can very well be a bad main drive gear ball bearing, or worn and broken layshaft bushings. If the condition of bearings and/or layshaft bushings has deteriorated to the point where either shaft is in misalignment, gear loading becomes excessive.
Frequent engine kickback when starting the machine can also have some effect on transmission gears. Normally a backfire would have little or no effect on a healthy gearbox, but consider how the gear teeth are jammed together when their normal direction is suddenly reversed. A worn layshaft bushing would aggravate crowding of the gear teeth and hasten formation of fractures.
SEATING THE RINGS
J own a 1965 Triumph Bonneville T120-R. Since I got it, it has been burning oil in the left cylinder because the exhaust shows a cloud of blue smoke when revved up. The plug on that side was covered with oil when I pulled it from the engine while cold. Also, oil seems to have settled around the exhaust and between the head and cylinder on that side of the engine.
The smoke only occurs when the engine is started cold and disappears after long running. What do you think is the problem? My dealer says the rings haven't seated but I know this takes place in the first few miles of running.
John L. Petro Ann Arbor, Michigan
Your problem may be a loose piston in the left cylinder. As the engine warms up the piston expands and takes up some of the excess clearance, which is why the machine smokes when cold. A loose piston should be detectable as knock when the engine is cold (piston slap). It is safe to assume that, unless you have mechanical problems, the rings will be fully seated in 300 miles.
As the machine is new and has done this since you bought it, it should be fixed under the warranty. If you have any further problems I would suggest that you write to the Triumph Corporation, Towson, Baltimore, Md.
