The Service Department
THE SERVICE DEPARTMENT
GORDON H. JENNINGS
ENGINE SWAPS
I have a 1961 MZ 125cc motorcycle and I would like to know if I could put a two-cylinder engine in its frame?
If so, what make and displacement would you recommend?
Eddie Foster Oak Lawn, Illinois
We have been getting a lot of letters from people who want to know about installing bigger engines in their motorcycles, so it would seem that this is a good time to make a general statement of policy in that regard. That policy is: "don't do it!"
Broadly speaking, you can get any engine into any frame, provided you are willing to do a bit of cutting and piecing, but just because you get it bolted in and chained to the rear wheel does not mean that your troubles are over. Chain pull goes up with horsepower, and you may find that the increased power will actually pull the rear wheel out of alignment every time full throttle is used. At best this will make the bike handle very peculiarly; at worst it will create a problem with thrown chains and/or abnormally high chain and sprocket wear.
Then, if you get enough extra bracing and gusseting to hold the power, you are likely to find that a larger rear tire is needed to get the power to the ground. And, with the added weight and speed, the brakes will probably no longer be adequate for the job they are asked to do.
Add to these possible problems all of the difficulties of designing and fabricating new engine and transmission mounts, and you have a long, uphill struggle ahead before the bike will be performing properly. In all but a few rare instances, the results really do not justify the struggle. Fewer problems will be encountered when switching engines of bikes having approximately equal displacements, but even then there is some doubt if the end product is adequate compensation for all of the time and money that will have been spent. In the end, one's time would be better rewarded if spent in a part time job — the pay being saved for a new motorcycle that more nearly meets one's requirements.
THE METRIC SYSTEM
I own a Yamaha TD1, and I am looking for a metric dial gauge for checking engine time. So far I have not had any luck and would appreciate it very much if you can help me.
Peter De Jong
Regina, Saskatchewan, Canada
Probably the only way to get a dialindicating micrometer calibrated in millimeters is to order the instrument from Europe. Neither Canada nor the U.S.A. has, as yet, seen fit to adopt the excellent metric system, and appropriately calibrated measuring devices are comparatively rare.
However, it is really not necessary to go to all that trouble. You can use conversion factors to change metric specifications into inches, feet, etc.
One meter is 39.37 inches; a centimeter is one hundredth of that, or .3937"; and a millimeter is one thousandth of a meter, or .03937". To convert, for example, 10 millimeters into an inch equivalent, multiply by .03937, the result being .3937".
All metric system units break down into tens, hundreds, thousands, etc. The meter is the unit of distance; the liter is the unit of volume, and one liter is 1000 cubic centimeters — one cubic centimeter being the equivalént of .061 cubic inch. Or, to put it in the most convenient and useful terms, one liter (lOOOcc) is equal to 61.02 cubic inches.
Similar conversion factors (with more detailed explanations) can be found in any reference library, and by means of these all metric system values can be converted into our familiar, if hideously illogical, patchwork system of inches, feet, gallons, yards, rods, miles and the rest. Perhaps the day will come when we too will adopt the more rational metric system and all this converting will be unnecessary.
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MISSED SHIFTS
I have a 1959 Triumph Bonneville with transmission trouble. My problem is that the transmission sometimes misses a gear and finds a neutral when shifting from 1st to 2nd. It is more evident when shifting at high rpm. When rounding a corner it will always miss the shift.
The bike has been completely rebuilt, and at that time I installed a new cam plate in the transmission. This seemed to help some, but did not completely cure the trouble, which is even worse now. At one time the brass bushing the cam plate rides in came loose. Since then the transmission has shifted worse than ever. Now it sometimes drops out of 4th, and finds the neutral between 3rd and 4th. The transmission has always had plenty of oil.
No one can seem to help me with this problem; I would be very grateful if you people can.
Marvin L. Beekman
Oklahoma City, Oklahoma
All progressive shift transmissions have a tendency to "overshoot" a gear and stop in the next neutral, and that would account for a part of your difficulties. It is a characteristic of motorcycle transmissions in general.
However, I would guess that your particular problem comes from having a wellworn transmission. A little wear on the faces of the shifting forks, multiplied by a little more wear between the forks and the cam plate, by a little more wear in the mechanism that ratchets the cam plate, and you have an accumulated wear in the overall shifting mechanism that will prevent the gear engagement dogs from sliding completely "home." Then, if the dogs themselves are a bit worn, and if wear is sufficient to allow a bit of endplay in the entire gear set, the transmission will fail to catch gears as it should, or will occasionally kick out of engagement, or both. A little wear in the detent that drops into the notches in the cam plate to hold the gears engaged will also cause trouble. And, it is even possible that the spring behind the detent has lost some of its tension.
The solution to this type of problem is obvious, and it is expensive. But, there is little else that will affect a permanent cure. Simply replacing one part in the long series of parts that takes the motion from the shift lever to the gears will make only a slight, and short-lived improvement.
The shifting action of new transmissions can sometimes be improved upon by lightening the cam plate. The inertia of the cam plate, shifting forks, and the sliding gears will always tend to carry the transmission right through the gear the rider is trying to select and into the following neutral — or even the next gear. It is the function of the cam plate detent to halt the process when the appropriate gear is fully engaged, and lightening the cam plate will give the detent less mass to stop. Lightening all of the moving parts would be desirable, but it is both dangerous (from the standpoint of reliability) and difficult to trim any metal from the sliding gears. Some lightening can often be done on the shifting forks, but this must be done with extreme care if weakening of the forks is to be avoided.
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In some transmissions, an improvement may also be made by grinding back the end of every other tooth on the engagement dogs. This gives, in effect, a wider gap between meshing teeth, and the dogs are more likely to slide into mesh when there is a great speed differential between them. In many transmissions this is a design feature; in a few others there is an odd number of teeth on the dogs, and it is not advisable to grind any of the teeth, as that would leave either two long or two short dogs together.
SUPER ZAP-FIRE PLUGS
I would like to know if anyone has tried a new type of plug called the "Fireplug?" This used to be advertised á lot, but I don't see it any more so I suppose the big ones have eaten the company up.
If those Fireplugs were good enough to fire jet engines and for the army to use in trucks, they might be good for cycles. Le Roy J. Nessen Nashville, Tennessee
For a time, which now seems to have passed, there was a whole rash of offbeat spark plugs offered for sale; most of them with names like "Fireplug," or "Super Zap-Fire." All of these were supposed to have been used in jet engines, and all were supposed to make old engines perform like new —and new engines develop 50% more power. Great claims were also made for increased fuel economy and there was usually some reference to a "last forever" guarantee.
It would be nice if all this were true; unfortunately it isn't. In the first place, a jet engine igniter has a completely different, and much less difficult job to perform than a plug for a motorcycle engine, and the igniter would be utterly useless for our purposes.
Secondly, there is no spark plug in the world that will make an engine deliver more power or economy unless the engine in question was already suffering from misfiring due to fouled plugs. If the plug fires the mixture at all, then a bigger spark will have no effect whatever.
Finally, competition between the major manufacturers of spark plugs is keen enough to insure that we, the customers, will always get the best plugs possible at the existing level of our overall technology. In virtually every instance, the man who is having plug troubles has simply not found ¿he proper plug heat range for his bike's engine. When the right plug is found (and the plug will be available in the conventional pattern), plug performance will be satisfactory.
There are a few special types of plugs being made today. An example is the surface-fire plug specified for some Saab (a Swedish automobile) two-stroke engines. In these surface-fire plugs, the nose of the plug is entirely filled with ceramic, and the spark fires across the ceramic between the electrode and the outer plug body. The plug will not "whisker" (for a variety of reasons), and it does not oilfoul — which makes it particularly well suited to two-stroke engines. However, this plug will only work when used in conjunction with a special ignition system, and its only advantage is that it does not foul. The power output of the Saab engine will be the same with the surface fire plug, or with a clean plug of the conventional pattern.
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STRAIGHT PIPES
I have a 125cc Ducati Bronco. During weekends I sometimes take it up in the woods to do some trail riding.
Since my muffler is so close to the ground and is easily dented, I removed it for trail riding.
Is the removal of the muffler hard oh my motorcycle?
Richard C. Ferguson Tacoma, Washington
Strictly speaking, removing the muffler, without making any change in carburetor jetting, has a bad effect on an engine. With the muffler removed, exhaust pulses have a tendency to over-scavenge the cylinder at some engine speeds, and the mixture may go "lean," just as it does when a megaphone is added to a straight pipe. However, in a relatively mildly-tuned engine, such as yours, the leaning of the mixture will not be of enough consequence to harm the engine. This is especially true if the engine is not run at full throttle too much.
If you do plan to do much full-throttle running with the muffler removed, I would suggest that you obtain a jet about one stage richer than the one that is correct with the muffler in place. Then, when you pull off the muffler, you can just pop in the richer main jet and all doubt will be removed. The engine may last longer — and I am sure that you will feel better about the situation. •
