The Service Department
THE SERVICE DEPARTMENT
GORDON H. JENNINGS
BMW SPEED-TUNING
Some time ago, someone wrote to you and said that with some modification the BMW R-69S would be capable of 150 mph.
Since I am currently the owner of an R60 and an R50, I am considering an R69S. I have written to the factory asking how the R69S can be made to go a little better and I have just received an answer. I believe that this information will be of interest to quite a few people. The procedure is as follows:
A) Mill down the cylinders, on the cylinder head face, approximately 1 mm (.039-in.). This will give a compression ratio of 10:1.
B) The ports must be enlarged, and smoothed, big enough to fit the 30mm Dellorto carburetor.
I was informed that the special cam (Rennsport) is not available, but that the stock 69S cam would be sufficient. With the engine modifications outlined, the factory advised me that the power would be increased to 50 bhp at 72000 rpm.
C) The rear end must be modified for a final drive of 2.91:1 (11/32 teeth); stock is 3.13:1 (8/25 teeth).
With these changes, the machine should be able to better 117 mph, taking into consideration the bulk of the rider, etc. For safety reasons, the factory suggests that racing tires be fitted, because the tires standard on the R69S are tested only to 109 mph.
Even after this work is done, there would be no noticeable increase in the time over the quarter, according to the factory.
If anyone is interested in other information, I suggest that he write a letter direct to BMW. The address is:
Bayerische Motoren Werke AG München 13, Leschenauer Strasse 76 Munich, Germany Thank you. Paul Nauck San Bernardino, California And thanks to you, Paul Nauck.
GRIPE, GRIPE, GRIPE!
Whoever wrote the test report of the Velocette Venom Clubman Veeline is sadly out of touch.
To take things as they occur: the name “Clubman” indicates that the model is in production racing trim. Hence, the closeratio gears and sports fairing; wider-ratio gears and a more comprehensive fairing come with touring models. Also, the fairing does not determine the position of the footrests, etc.; the touring model has a fairing and conventional footrest positioning.
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Not only the early version of the MSS, as stated, but the Venom, Viper, and Scrambles models have aluminum barrels, and looking at your photographs, I feel sure they haven’t changed for 1963.
I assume that the BHB Company is the U.S. distributor for the desmodromic kit marketed in England. If so, then their claim of 9000 rpm and a 3 to 5 bhp increase is pure sales talk, as the cam forms are standard and the only benefit is safety.
If starting the Velocette was an annoyance to the tester, I can only suggest he read the rider’s handbook and learn the correct way to start a Velocette; after which he would find it invariably a firstkick starter.
Adjusting the rear spring units in the slots does not adjust the damper action as the tester states; that adjustment is on springing only. Also, I doubt very much if the units have the 3 position cam adjustments in addition to the accurate slots. The units are usually Woodhead Monroe; not Girling.
In conclusion, may I say that if your tester was more familiar with the Velocette he would be aware of the much higher quality than is usual with English ma-
chines, something test figures do not show but which the tester should bring to the notice of the reader. Your article certainly doesn’t flatter the Velocette.
Harry Webster
Mill Valley, California
It is not our intention that the test reports in CYCLE WORLD flatter any motorcycle; we say what we think, and report the facts as we know them, and that is that.
In the first place, we know that there is a Velocette with a fairing somewhat better suited to generaI touring than the one used on the Clubman. However, the Clubman was the machine being tested.
As for the matter of cylinder materials, the motorcycle we tested did in fact have a cast-iron barret. Knowing that the Velocette had featured a light-alloy cylinder, we almost failed to notice that a change had been made, for the cylinder was very prettily painted so that it looked like aluminum. Unfortunately, the cylinder “flunked” our magnet test, which proves that while there is some chance that it might not be cast-iron, it is clearly a ferrous material and not aluminum.
Moving the spring/damper units forward in their slots softens both the springing and damping action_ — and for the same reason: with the units angled forward, a given amount of motion at the wheel produces less telescoping of the unit. Also, we would like to restate the fact that there really was a 3-position adjustment on each unit.
Starting the Velocette was a struggle every time, and we tried every combination of spark, throttle, choke, “tickling” and just plain cursing and prayer known to man. The starter system just does not allow a really rapid run-through, and that is what is required to light-off one of these big singles.
You have a point, of a sort, in the matter of the desmodromic valve gear. Granted, if the valve timing is unchanged, the conversion to positively opened and closed valves will have only a slight effect on power, at best, but this method of valve actuation makes it possible to turn the engine much faster than can be done with the stock setup, and this feature, in conjunction with modified valve timing — even if only the opening and closing rates and not the open and closed periods are changed — will increase the engine’s power output. And, sometimes a bit more power can be obtained with desmodromic valve actuation simply because the valves are following the cams more accurately at high speeds.
Finally, there is the matter of finish which, on the Velocette we had) is neither better nor worse than that of other high price-bracket English machinery. Judged on an absolute basis, the Velocette’s overall finish is, of course, quite good, and if we have failed to give it its due, then for that we are sincerely sorry.
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AND BMW CORNERING
I am a young Mexican motorcycle enthusiast. In my neighborhood, I am a special BMW enthusiast; in theory, because I have never ridden one.
My friends tell me about the “great” BMW disadvantage in cornering because of the low, horizontal cylinders. How big a disadvantage is this? How much does it limit high speed cornering?
Carlos Tejeda Mexico 20, D.F.
Mexico
Insofar as the stock BMW motorcycle is concerned, the protruding cylinders are not particularly disadvantageous. The machine is intended primarily for touring, and is quite softly suspended, and few riders would care to crank it over until the cylinder heads began to scrape. And, on the standard BMW, the engine is mounted high enough in the frame to clear the paving even if it was leaned over very sharply. When at its running height, the BMW can be tilted about 50-degrees, and then it is the foot-pegs that "ground”; not the cylinder heads.
For racing, on the other hand, the extended cylinder heads are a very real disadvantage. A few years ago, they would not have been, but the high-hysteresis (cling-rubber) tire has changed all that. Today’s racing tires provide such a tremendous grip that one may corner faster and lean farther than ever before. A flattwin BMW, all tricked out with racing suspension and these tires, would almost surely be scraping the cylinder heads if it was cornered as fast as the tires would permit.
BIG-INCH TWO-STROKES
Could you give me the names of any motors or motorcycles being manufactured with more than 250cc displacement in a single cylinder? What are some of the largest you know of?
I am riding a Zundapp Super Sabre and a Harley-Davidson 74 currently.
Dan Utke
Enderlin, North Dakota
No, right at the moment I cannot think of any motorcycles having two-stroke engines with unit cylinder displacements of over 250cc. That seems to be just about the limit, and there is a lot of evidence that indicates that a better limit, from the
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standpoint of power, would be just half that: 125cc.
There is a lot of huffing and puffing going on inside the cylinder of a crankcase-scavenged two-stroke engine, and in large cylinders, the intake and exhaust gases have a tendency to get confused about just which way it is that they are supposed to travel. In smaller cylinders, where the gas streams can be held in close proximity to the confines of piston crown, cylinder walls and cylinder head, it is somewhat easier to control the gas flow.
Also, the smaller cylinder is a better proposition from the standpoint of cooling. Piston cooling, particularly, becomes very difficult as the cylinder bore is increased — which is one reason that 250cc two-stroke singles are usually made with relatively long strokes and small bores.
There are some large displacement (per unit cylinder) two-strokes. One is the GMC two-stroke diesel truck engine, which has,
l understand, 71 cubic inches displacement per cylinder. And, there are two-stroke diesels used in ships that have enormous cylinders — I have seen men stand down in these bores looking for wear with a flashlight. However, these big two-strokes are all diesels, and almost all of them use uniflow scavenging, pumping air (from a supercharger) in through a ring of ports at the bottoms of the bores and exhausting through poppet valves in their cylinderheads. Piston cooling is much better when the hot exhaust gases are not blown over the edge of the piston as they leave the cylinder. Even here, though, cooling is a problem and often there are passages leading up into the piston crown, and oil is circulated through the piston to provide adequate cooling. This is, of course, quite out of the question for the small motorcycle engine and for this, and the other reasons outlined, we are not likely to see any big-inch motorcycle two-strokes. •
