Royal Enfield Motorcycles

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Royal Enfield 1916

Royal Enfield 1916 3 1/2hp

(L) Valve side, showing auxiliary petrol tank connection to starting jet in induction pipe, the latter being lagged.
(R) Note the hot air intake and petrol pipe bearing against back cylinder. This view also shows the stop for kick starter.

Royal Enfield 1916 3 1/2hp

Forcing grease into the Enfield gear by the use of a grease gun. This is a more permanent way of oiling than the usual method.

Road Experiences with a 3 h.p. Enfield.

A Commentary embodying some Valuable Riding Hints by a Practical Owner.

FOR some weeks past I have ridden, almost daily, a latest model 3 h.p. twin Enfield, and as this machine belongs to a class which may be regarded as very desirable from the point of view of the solo rider, a few notes regarding its running will probably be of interest.

In these days of all-round perfection, it is often very difficult to decide whether a small twin, on the lines of the Enfield, or a 31/2 h.p. "single," is the better adapted to one's requirements. On the one side we have vibrationless running, speed on the level, and extreme economy; on the other side we have a wonderfully docile engine, power on hills, and a machine which requires an absolute minimum of attention. The tendency of design with small twin cylinders today is to produce an engine that will "rev" indefinitely, and one of the great secrets in handling such an engine lies in "keeping up the revs " - particularly when using a heavy fuel. The charm of a perfectly even torque, smooth and rapid acceleration, a silent exhaust, and vibrationless running must be experienced to be appreciated.

Speed and Economy.

The Enfield possesses three excellent features. The first is its remarkable economy, the second its smooth running at all speeds, the third the extraordinary speeds the engine is capable of attaining and maintaining.

As regards economy, I have not tried to achieve anything unusual in fuel consumption. Riding in a mountainous district the consumption averages out at 88 m.p.g., but I have not the least doubt that, at a slight sacrifice of power, one could obtain 110-120 m.p.g. as a regular thing. I have ridden Enfields that do 140 m.p.g., but they were not remarkable for vitality. Economy in tyres and transmission interests me much more than m.p.g., for the former rests with the designer, while the latter rests chiefly with the rider or tuner. The rear tyre on my machine is very little worn after 3,000 miles. It should do 5,000 on the back and 2,000 on the front without risk - barring cuts. The front tyre would almost sell as new, and the chains are perfect.

The Enfield transmission system is really excellent. I have locked up the slipping ring device, yet there is not the faintest suggestion of snag till the engine absolutely konks out. Even when the machine jogs along on one cylinder for a few yards - as it often does with a heavy fuel - no suggestion of solidity in the drive is conveyed to the rider.

This accounts, of course, for the unusual tyre wear, while it has not a little to do with the vibrationless running. The machine "zips" along at 37 m.p.h. without a tremor, and is good for an occasional burst of 50 m.p.h. with no danger of overheating. Riding between London and Leeds, it is 3 m.p.h. faster than my last 3½ h.p. single, and that single was no sluggard.

All things considered, the Enfield is quite a cheerful little beast. One can drive out all day without touching one's pocket or a spanner. It purrs up our interminable mountain slopes at 22 m.p.h. on low gear, taking top without a murmur immediately the gradient slackens, and withal it is absurdly cheap to run! But it requires more attention than, say, anything so monotonously reliable as a Triumph or P. and M.

Heavy Fuels - An Unsolved Problem.

The running of the machine was perfect in every way till, from stern business necessity, heavy fuels became the daily order. Then the band began to play. For a week or so the engine runs as well on the heaviest of mixtures as it does on petrol, but at the end of the week irregular and faulty running sets in. The engine never lacks power; it merely cuts out on one cylinder or fires irregularly. The most careful search has been made for air leaks, the ignition system thoroughly overhauled, and carburetter minutely examined. The fault is never cured; it merely cures itself.

Certain fittings were, of course, necessary ere the machine could be run with safety and satisfaction on heavy mixtures. With the Enfield it is particularly necessary to guard against bad carburation, for the oil is circulated through the engine by means of pumps, the surplus being returned to the oil tank. Neglect of obvious rules would lead to the oil becoming thinned, with resultant worn bearings, and probably a seized piston. The obvious rules are: Fit an efficient hot air intake; if the induction pipe is of any length, lag it to prevent the escape of heat; if possible, warm the fuel before it reaches the float chamber, and keep it warm while it rests in the float chamber.

The hot air intake was made out of the bend of an old double twist horn. Nothing better could have been arrived at, the bend being wider at one end than at the other, so that the hot air is drawn from an ample surface. The end of the pipe which 6ts up against the cylinder is deeply grooved, so that it draws air actually from between the fins. The bend is lagged with insulation tape, it being made of such thin stuff that it is not capable of retaining heat. This arrangement, I find, is quite sufficient to warm the whole carburetter, and it may be " added that the function of a hot air intake is not merely to supply warm air, but to warm up the whole of the carburetter body. Unless it does this it cannot be regarded as efficient, as the carburetter is a massive piece of metal, which will absorb the warmth of the vaporised fuel if the metal be at atmospheric temperature or below.

Royal Enfield 1916 3 1/2hp

Copper clip for warming float chamber.

Warming the Float Chamber. The fuel pipe from the tank was next shaped so that it bore hard against the back cylinder for the greater part of its length, and by this means the fuel is brought well above atmospheric temperature ere it reaches the float chamber. It remains there, however, quite long enough to cool down, and the next problem was to warm the float chamber by some means. To effect this a copper clip was made to fasten round the float chamber as shown in the sketch, its ends bearing hard against the back cylinder. Normally, the clip is too hot to hold at A, and quite perceptibly above the temperature of one's hand at B. When the machine is stationary, or after much low gear work, it is quite hot at C, and thus it cannot be doubted that it imparts an appreciable degree of warmth to the float chamber.

With these fitments the machine was subjected to a practical road test on a fuel a good deal heavier than it was ever intended to use, but there were distinct symptoms of imperfect carburation. It was then pretty clear that bad carburation was not the fault; condensation was the culprit, and accordingly the induction pipe was heavily lagged with asbestos twine, wrapped over with insulation tape. This made all the difference in the world, and, except for the occasional fits already alluded to, the heavy fuel problem is mastered. That the heavy fuel does have some effect upon the lubricating oil is proved by the rapid discolouration of the oil when a heavy fuel is used. After circulating a few times it becomes a deep brown - almost black - whereas, with petrol as the fuel, the oil in the tank retains its greenish tinge till the tank is drained. But there are no indications that wear in the engine is taking place.

Enfield Lubrication System.

Many riders of Enfield machines have hesitated to adopt heavy fuels on account of the lubricating system. If bad carburation occurred the fuel would escape past the piston rings and gain the oil in the crank case, and, since the oil is constantly circulating, it would absorb more and more of the fuel, thus becoming dangerously thinned. Perfect carburation is, of course, the only safeguard against this, and if the fitments described be adopted, I do not think there is the least danger in using heavy fuels on the machine under review. So far as starting goes, an injection of petrol is all that is required, but to avoid the nuisance of carrying an injector, which is apt to run dry, I have fitted my machine with a small petrol tank, which is connected up to a pilot jet fitted into the induction pipe. By turning on the tap under the small tank it is thus possible to flood the induction pipe with petrol, and a very easy start is made.

Returning to the lubricating system, this is much preferable to the ordinary drip feed, as it is economical and requires no attention while on the road. But just as in the case of the drip feed the absent-minded rider forgets to push down the plunger and thus starves his engine, so, in the case of the Enfield system, he forgets to turn off the oil on reaching his garage, and next morning the contents of his oil tank have percolated through into the engine. The engine then remains filthy externally till next cleaned, though, when started up, the pump returns the oil to the tank in a few seconds. Still the system would be much improved if it were not necessary to turn off the oil when garaging the machine.

The gravity feed to the wall of the front cylinder is a necessity, and I find that if I omit to turn this on, the top. piston ring of the front cylinder gums up in 500 miles. I have removed the bottom ring from the front piston, and this has also helped to cure the sticking of the top ring.

Ignition System.

The Thomson-Bennett magneto is a well designed and remarkably accessible little instrument which any novice can take to pieces and replace without difficulty; but the one on my machine possesses one fault. It is not waterproof.

With the usual thoroughness of workmanship manifest throughout the design of the instrument, thin packings are inset round the edges of the aluminium end plates, which draw up against the magnets at either end, but there is evidently just enough spring in the aluminium plates to cause the joints to gape open at the top. This I have cured by fitting a simple clip, which serves to draw the joints well home. There should, of course, be no necessity for such gadgets, but before the addition of the clip I was troubled by water getting in and rusting the armature and magnets.

It has often occurred to me how much more handy it would be if hexagon-headed setscrews were used throughout in magneto construction instead of the counter-sunk screws, which require the use of a screwdriver, the latter being quite an inadequate instrument when a screw has become rusted in. If this were done the key provided for contact breaker adjustment would be the only tool required to take the magneto apart.

Two-speed Gear.

At first I was not. particularly in love with the gear, though I found it a vast improvement on the simple dog-clutch mechanism of my last semi-lightweight. It has, however, improved immensely with running, and now leaves nothing to be desired - unless possibly a combination (hand and foot) control. I can start off with perfect smoothness on a 1 in 5 gradient, and such feats were impossible when the gear was new.

I have ceased using oil for this gear and now use vaseline or gear grease, which is forced in by the use of a grease pump having a screw-down plunger. I find this way of lubricating far more permanent than the usual method.


The kick-starter is rather apt to stick, automatically releasing itself at the exact moment when one's left shin is in its direct line of travel. I have improved it very considerably by fitting a stop. This prevents the crank from attaining a position from which the necessary push forward can be given only after manoeuvring the crank over dead centre.

All things considered, the 3 h.p. Enfield is a very desirable solo mount. It is cheaper to run and less tiring to ride than most 31/2 h.p. singles I have possessed, and for speed it is distinctly superior to the average "big single." That it periodically objects to heavy fuels is no criticism of the machine, itself, as any aristocratic mount would object to some of the obnoxious mixtures today sold as motor fuel.


The Motor Cycle November 30th, 1916. Page 472

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