Road Test

LIKE MANY ANOTHER old-line firearms manufacturer, Birmingham Small Arms, or BSA, has found a profitable diversion in the design and construction of motorcycles. Indeed, the diversion has become the main order of business, and we motorcyclists are much the richer for its having done so. After all, (with apologies to someone or other) a gun is only a small bang, while a good motorcycle is truly a blast. And, BSA Motor Cycles Ltd. is currently producing a whole series of such blasts, ranging in size from I25cc alt the way to 650cc, and our test is concerned with the newest offering in the latter category-: the very advanced A65 Royal Star 650.

Of central interest in the new BSA is its engine, which is an all-new design that will ultimately, we arc sure, replace (in one form or another) all of the existing big-twin BSA engines. It is, at its very heart, a much more modern engine than the others in the line (although there certainly is not anything wrong with those others) by virtue of the nearly I: I bore/stroke ratio, and because it is all gathered into a unit, with the clutch and transmission. The various mechanical elements, instead of being bolted up into an untidy and oil-leaking clump, are all inside a single housing.

The effort to limit the number of potentially leaky joints starts up at the top of the cylindcrhead. where all of the valve gear is collected into a single, cast-on chest, with a onc-piccc cover secured by six healthy-sized studs. The valve-actuation originates down at a single camshaft, and comes up via radius-faced light-weight tappets and pushrods between the cylinders to the center of the cylindcrhcad. AH of the pushrod passages arc cast into the cylindcrblock (which is of cast alloy iron) and the cylinderhcad (of aluminum.) It is all very neat, and very, very oil-tight.
Apart from being oil-tight, the cylinderhcad has a couple of other important features. The ports arc large, and without flow restricting obstacles of any sort, and the exhaust ports are splayed outward to a marked extent-This is partly to enable the exhaust pipes to clear the frame, but more important, it leaves the forward part of the cylindcrhcad open so that air can get to the area around the exhaust valve scats. The valve chest helps to channel the air through the center of the head, and the finning there is arranged so that (he air is led out past the spark plugs. Of course, the power obtained from this engine is nothing remarkable, but one should realize that the relatively small single carburetor is the limiting factor here; not the valves or porting. Anytime BSA. or anyone, wants more power from this new engine, all they have to do is change the valve-timing and compression ratio (both rather mild at present), add another carburetor, and there should be another 10 bhp in the engine without making it over-tuned.

While on the subject of power output, it is worth mentioning that BSA's American distributors, in common with a few others, do not release any power figures for their machines. To make an accurate statement of output would place them at a sales disadvantage, and to boost the claim would be dishonest, so they have simply withdrawn from the whole silly business. However, we have figures on this engine, from England, and we will tell you that it has a real, honest-to-goodncss 38 bhp. The honesty of this figure is confirmed by the bike's performance, which is embarrassingly near being equal to that of others having much higher advertised horsepower. The truth will out.

At its lower end. the BSA engine is much like those that have gone before it, with plain-bearing connecting
rods and timing-side main; the heavily-loaded output end of the shaft has a ball-bearing. On the timing end of the shaft is the skew-gear oil-pump drive, and the three-gear drive for the camshaft. The center, idler, gear in this set also drives the ignition breaker (which is. incidentally, housed inside the crankcasc end cover, with access provided by a small, round inspection plate.)

The output end of the crankshaft carries a three-row sprocket for the triplex primary chain, and outboard of the sprocket is an alternator. This alternator charges the battery, after a rectifier changes its output from AC to DC. and there is an emergency circuit for feeding the output direct to the ignition system so that the bike can be kick-started when the battery is down.
The triplex primary drive is absolutely lash-free. A blade-type tensioner takes up any slack in the chain and the clutch hub incorporates u synthetic-rubber cushion to take out any snatch or pounding that gets past the tensioner (or just any drive vibrations, period.) The clutch itself has bonded linings, and is completely conventional and completely satisfactory.
The transmission gears are all contained in a compartment cast on the back of the crankcase, and here again everything is very conventional and very satisfactory. The shift mechanism gives a light action, and while it had a tendency to bounce back, instead of dropping into engagement, when being speed-shifted, it was otherwise very good.
This package, the engine and transmission, are set into a two down-tube frame that owes at least as much to the mass of mctalinvolved as it does to efficient placement of tubes, but which docs the job asked of it. The engine mounting has. we understand, been modified in all of the machines produced after our test bike (which was one of the very first off the production line) to improve smoothness. This leaves us somewhat at a loss, because we had already decided that the BSA was just about the smoothest bike we had ever ridden, and that was with the old "rough" mounting.

The riding position offered by the placement of the BSA's saddle, handlebars and foot-pegs was nearly all that anyone could ask of a touring bike. The chin-down, feet-up, monkcy-on-a-stick position featured by some semi-racing machines is nice for an hour or so of afternoon sport, but it is by no means as comfortable for touring as the sit-up BSA arrangement. We would have preferred that the handlebars be a trifle lower and straighter for high-speed touring, as the "western" bars supplied with the bike hold the rider a little too upright and splitting the breeze. It was, on the other hand, just the thing for about-town travels.

Out on the open road, the Royal Star really lives. The comparatively tall gearing gives a high cruising speed
with a minimum of engine churning and this, coupled with the excellent ride, makes this bike exceedingly smooth. The new BSA would flit along at 70 mph, with a lack of strain that should be the envy and despair of a host of lesser machines.
High speed work and acceleration trials were a great pleasure. The Royal Star has terrific stability (so good, in fact, that we never found it necessary to tighten the steering damper more than just enough to keep it from rattling around loose) and the engine is not the least bit fussy about anything. Even though the engine's power peak is at 5800 rpm. it will continue to wind-on up to 6400 rpm before the power fades away appreciably. And, of course, the engine is so mildly tuned that the power does not come in only at the tap end; it is there almost from an idle, and it made standing-start acceleration runs a snap. With so much low-end torque, the BSA comes away from the mark like it was shot from a bow. Naturally, the torque is very useful in touring, too: the rider can, without bothering to drop down a gear, or anything, simply turn on the power faucet and go flying away. This kind of torque is the next thing to an automatic transmission. i
The low end performance is matched by the top speed, too. Indeed, the respectable 106 mph top could be still further increased by a small change in overall gearing. At the top end, the Royal Star has climbed past the engine's peaking speed and it would go a bit faster, probably a bit over 110, with a lower overall ratio. Conversely, the lower end performance would suffer, and for the vast majority of riders, the stock gearing would be perfect.

Our test machine was loaned to us by "Mr. BSAVAub LeBard. of LcBard 4 Underwood in Los Angeles.
All things considered, the BSA Royal Star 650 must be rated as absolutely top flight. Without being fussy, it gives extremely brisk performance and economy of operation that is not bettered by much else near its size. In addition, it has a solid feel that indicates great reliability, and the overall appearance — contributed to by both its finish and the tidy enclosure of the machinery — is of the highest order. And, oh yes, it has big. soft-action brakes that balance nicely its speed and weight. In short, this newest BSA is in all ways a really first rate motorcycle; we recommend it most highly. •

Source Cycle World