SPORTING MACHINES ON TEST. THE MODEL 90 SUNBEAM. BY THE ASSISTANT EDITOR.
I T has been our duty to ride many sports models, and our pleasure to ride a few. The 493 c.c. Sunbeam definitely falls in the latter category.
The impression we had on first getting astride the machine was one of complete controlability, the saddle position being extremely low and comfortable. For a machine of considerable weight, the feeling is one of great compactness.
The machine we took over was actually a T.T. reserve, and as such, we expected a certain amount of intractability. The compression ratio of the two-port engine was in the neighbourhood of seven to one, while the low gear was about eight to one, factors which do not make for extreme docility at low speeds. In addition a further embarrassment was the twist grip control, a method we had hitherto never tried.
Despite all this, however, we were able to start the engine at Euston Station and drive it out of Town to our home in the country twenty-five miles away, with perfect ease. In traffic certainly, a certain amount of dexterity is required to keep the engine revving, as the machine is liable to spit and bang at low engine speeds. This, however, is probably due to the carburetter setting, and could be cured by adjustment.
On the open road, however, the machine came into its own. Our way lay over one of the new bye-pass roads, and here we opened out a little, to get the feel of the machine at reasonable speeds. The piston, which slaps steadily up to about fifty or sixty miles an hour, grew silent, the deep exhaust note rose slightly, and the road began to fly from under our wheels. At half throttle we seemed to be doing a
gentle seventy or so, the machine rock-steady under us.
Further on, an open stretch of bye-pass tenipted us yet further, and we opened flat out. A speedometer was not fitted to this machine, but the acceleration from seventy onwards was tremendous, and far in advance of any other sports model we have ever tried, except a certain big twin. The engine appeared to be accelerating from twenty miles an hour, so terrific was the increase in speed. We must have been travelling around eighty-five, when we shot on to a section of road which had recently been I up: We had not tightened either the steering damper or shock absorbers, and with the extreme springiness of the Terry saddle, we leapt and Charlestoned about a hundred yards, before regaining equanimity and equilibrium
. Throughout this little exhibition of what not to do, the machine had complete control, we simply hung on with our hands, having lost the footrests. But with the machine controlling us, all was well, and we were never in any danger of crashing. There was nothing like a wobble, but simply a pitching and tossing fore and aft motion, and this would probably not have happened, if we had made intelligent use of the damper and shock absorbers.
The steering damper is of interest, as it can be adjusted while in motion with one finger, so gentle is the action required. The front fork shock absorbers are also provided with a finger nut for adjustment from the saddle, very useful items on a fast machine.
We next rode the machine across country in pouring rain and over rain sodden lanes, deep with the fallen leaves and thick mud of Autumn. Despite these coneitions, we were able to proceed at speed, without the slightest suspicion of a skid.
Only once indeed, did we have this, and that was owning to forgetfulness and a sudden jerk open of the throttle. Although in top gear, the rear wheel waltzed in a thrilling manner, but we successfully retained our seat.
Having an appointment at Brooklands next day, we decided to use the Sunbeam to keep it, and set off over treacherous roads amid a drizzle of rain.
Already confident in the road holding qualities of the Sunbeam, we were able to maintain a high average, and by judicious use of steering damper and shock absorbers, successfully negotiated some roads notorious for their badness, notably the road from Richmansworth to Denham, and across the Uxbridge-Slough road to Colnbrook.
On this latter section, again neglecting the shock absorbers, we succeeded in denting the front mudguard with the bottom of the forks, while striking a pot-hole two inches deep at about forty miles an hour. The shock, which would have sent us over the handle bars of some machines we could mention, did not disturb the steering in the least.
We arrived at the Track very wet, for the model 90 was equipped with T.T. mudguards as well as a T.T. engine. After transacting our business, we took a run round the track, and then essayed a climb of the test bill.
We changed from bottom to middle as we crossed the line at the foot, and despite this, the machine accelerzted all the way to the top, to such purpose indeed, that we executed a hair raising leap into the air, at the summit moving at about forty miles an hour.
We landed in complete safety again, a good bit further on, thus • demonstrating again, the extremely excellent steering of the machine.
On the track itself, we were unable to get the best out of the engine, owing to shocking weather conditions, with rain and a high, gusty wind blowing. Knee grips were not fitted to this particular machine, and we felt their lack on the bumps of the track, which any who knows Brooklands will appreciate.
From what we saw of the machine, we should judge ninety miles an hour quite within the scope of the engine. Seventy and eighty are comparatively easy of attainment on any open bit of road, and at these speeds the engine is perfectly happy, more so indeed than at fifteen or twenty.
One adjustment we made, and this was to the footrests. These we moved to a higher position, owing to the excellent shocks we sustained from our very wet trench coat making contact with the plug top ! The finish of Sunbeam products is world famous, and needs no comment beyond saying that it is superlative. Thought in design is obvious in the most cursory glance. Instant adjustment by milled wheels is provided for both front and rear brakes. The front brake, by the
way, was the most efficient we have ever known, the slightest touch to the inverted lever alone being necessary, a welcome change after the frenzied clutch necessary to feel the front brake at all on many machines.
The valve gear was reasonably quiet, an item of interest being .the ” grass-hopper” valve springs employed. Lubrication is effected by sky sump, an oil tank being situated under the saddle, and provided with an auxiliary pump actuated by a lever on the handle-bar.
In the production model cable mechanism is employed for the rear brake, and a rod for the front, and a stand is provided for the front wheel.
Twin silencers are very effective and give a very deep, mellow note, which could not in any way be termed noisy.
Altogether, the machine approximates to the sportsman’s ideal, being very fast, with tremendous acceleration, very stable at speed, yet controllable at slow speeds. A few points of criticism, all of them trivial. The fuel consumption is on the high side, although this is of course to be expected with an ultra-efficient engine of this sort, driven as fast as this one was. The consumption
and slow running could both be greatly improved by a little judicious carburetter tuning.
Oil consumption, owing to the dry sump system, appeared to be practically nil.
The only breakages we suffered were the bolt anchoring the shock absorber, which snapped on hitting the king of all pot-holes at speed, and the fracture of the nipple between the float chamber and petrol pipe.
As these breakages were both due to excessive speed and excessive road surface, they may be dismissed as negligible.
Apart from these points the Model 90 presents a remarkable machine capable of displaying a rear number plate to almost anything on the road to-day. There is certainly no car in existence, and one or two motor cycles only, which could equal the Sunbeam’s performance over any distance. The Model 90 has to be ridden to be believed. It is almost incredible.
The price of this wondeiful machine with 1928 improvements will be 100 guineas.
Engine : 8 cylinders, 86 mm. bore, 108 mm. stroke, capacity 4,982 c.c. R.A.C. Rating 36.9 h.p. Overhead valves, push-rod operated. Coil ignition. Double vertical carburettor. Clutch-engaged Roots supercharger. Gear-box…
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