The Scott Two-stroke.
Although none of the modifications which will distinguish the 1912 Scott from that which has performed so creditably during the past season are very obvious, they are worthy of note, because they are the outcome of practical riding tests by the designer who has carried an original type to success.
Foremost in interest naturally comes the engine. To start with the bore has been increased 1/8 th of an inch and now measures 2 7/8 in. with a stroke of 2½ in., the cubic capacity of the cylinders being 535 c.c. as against the previous 485 c.c. The cylinders themselves have been completely remodelled, and are now a wonderfully smooth casting from which all dirt catching nooks and crannies have been entirely removed. This is indicated by the first illustration, which shows a pair of cylinders without the water jacketed head, mounted on the aluminium crank chamber. The latter has a rounded front instead of the previous square section, whilst it has been further strengthened by numerous reinforcing webs. Between the upper transfer port, which is on the side of the cylinder, and the lower transfer port, which is in the crank chamber, is a ridge of metal, which is machined to act as a guide for the transfer port covers and gauzes. It is, therefore, impossible to put these latter in any but the right position, and choking of the port following upon their incorrect situation is thereby avoided.
The joint between the cylinder casting and the crank case is formed by machined cups in the last named, into which rings turned on the base of the former register, the packing being made by a narrow linen washer.
An exceedingly clever and thoroughly practical device has been introduced to take the place of the usual holding-down bolt, the use of which necessitated four pockets for the nuts in the side of the easting. Instead of the usual bolt is a shouldered stud, the smaller diameter of which passes through a lug on the side of the crank chamber, and is threaded for its bolt in the ordinary way. The larger cylindrical shoulder lies inside a blind hole drilled in the water-jacket casting, where it is held in position by a knob-headed pin. In order to remove the cylinders all that it is necessary is to slacken the underneath nuts to a slight extent, when the securing pins are withdrawn and the cylinders free to be lifted clear.
The carburetter has been remodelled. The second illustration indicates that the arrangement remains the same. All the air for the mixture is taken past the jet (except that which may in special circumstances be allowed to enter through the jet cover), and it all comes from the space between the crank chamber walls, where it is not only warmed but free from dust. An automatic valve with an air cylinder dashpot controls the main air admission, and to allow for additional air adjustment the whole of this valve with its circular brass seating can be lifted to a certain extent above a second seating, this movement being accomplished by a screw action and operated by the lever shown on the right of the sketch. The spring against which this level works is contained within a closed brass cylinder, fixed on the near side of the air valve drum, which effectively shields it from dust, dirt, and water. A similar cover is used for the throttle sleeve.
The throttle valve consists of two concentric sleeves moving in opposite directions and giving a central cut-off immediately behind the jet. The moment the throttle is closed two air ports come into register and deliver fresh uncarburetted air to the inlet pipe. This air is also drawn from the crank chamber, the ports (the top of which can be distinguished in the sketch) opening out into a cast-in duct which leads thereto. The sleeve and handle controlling the jet cover have been strengthened as shown.
Not only has the appearance of the engine been made neater* by the hiding of the carburetter control springs, but a further effect in the same direction has been gained by having the control cranks pointing downwards, the Bowden wire to which they are attached being anchored in special lugs cast on the crank chamber (see sketch on previous page). The extra air valve and its seating can readily be removed by slackening the nut on the side of the drum which is partially split for locking purposes.
Turning now to the two-speed gear, this has been entirely re-designed and now runs on four large diameter ball races with 9-32in. diameter balls. Apart from this point, however, the wedge action, much is used to expand the hardened steel clutches, has been considerably improved, and is now so easy to operate that either gear can be put in (and will remain in) with the pressure of a finger. The sketch on the previous page illustrates half of the gear, showing the wedge action. The ends of the expanding rings are inclined towards one another, and into this converging gap are thrust a couple of hardened steel rollers supported in a cage. The peripheries of these rollers bear together, and as they roil upon one another the friction in producing the expanding action is very slight indeed. Their housing is carried by a sliding ring keyed to the centre spindle and operated by an internal push rod. The drive between the spindle and the expanding ring is, however, not taken through the wedging rollers but through a tongue made integral with the sliding ring, which engages with a key slot in the expanding ring. (In the sketch this tongue and slot are shown at the bottom of the clutch and the roller-wedge at the top.) The expanding clutches are fitted with specially hardened end pieces, and arc ground perfectly cylindrical, so that their pressure of contact with the outer drum is uniform around their periphery.
Sidecar attachment lugs are brazed to the frame at the steering head and also immediately in front of the back axle slots. The down tube, which forms the oil tank, has been increased in diameter, and the filler placed lower down, so that spilling out of the back tube is impossible.
An excellent point is that the spring footboards are now made completely and almost instantaneously removable (see sketch). In the rear the footboard is supported upon a sprung D tube, to which it is secured by a spring latch and a couple of claws on a brass lug. In front it is supported and also suspended by a single leaf spring which slips on to the end of the cross tube. It will be seen that, although the boards are detachable - a very handy thing in cleaning or adjusting - the machine can be safely leant upon them, as they cannot shift in an upward direction.
Amongst other minor improvements are : Petrol tank increased to two gallons capacity; adjustment of automatic oil-feed made quicker and self-locking; recessed pannier tool-bags in carrier; side wings of curved-form, die-stamped, and therefore quite rigid (these protect the front of the engine completely and are fitted with a bright stout aluminium beading which will stand any amount of scraping, etc., and look little the worse for it); larger diameter back wheel bearings, stronger spokes, and heavier rims; chain guard covers entire upper part of chain; enclosed magneto; shorter wheelbase (this is now 54½ in.); kick starter put forward of back axle, so as to he independent of driving chain adjustment.
Altogether the 1912 Scott will be in general considerably nearer perfection than the 1911 model, and this is high praise indeed. We are informed that the past somewhat restricted output is to doubled next year.
1911 Olympia Show - The Motor Cycle November 16th, 1911. Page 1220A
SCOTT, No. 125.
The Scott Engineering Co., Ltd., Mornington Works, Bradford. – As the Scott 1912 improvements were very completely dealt with in our last issue, it is unnecessary to do more than touch upon the more salient points. The first of these is the re-designing of the engine, making the cylinders and crank chamber much neater. A very ingenious device has been introduced for allowing the quick detachability of the cylinders, it being clever method of only necessary now to securing the Scott. Slack off the four cylinders to the crank security bolts and withdraw four pins, when the cylinders come away clear. The bore of the engine has been slightly increased. The two-speed counter-shaft gear has been improved in detail, and is now furnished throughout with ball bearings, even the wedge bar operating the clutches being also fitted with roller thrust blocks. The mudguarding on this machine leaves little to be desired. The side flaps on the front guard are utilised as number plates. This part of the guard is also detachable to allow the front tyre to be easily got at. The carburetter has been refined in several details, the springs for the return of the air and throttle valves being now housed in tubular brass cases.
The standard colour of Scott machines is a very pleasing shade of purple, and it need hardly be said that they represent some of the finest workmanship to be seen at Olympia. It will be difficult to get a Scott next year, judging by the order list we have seen.
1911 Olympia Show - The Motor Cycle November 23rd, 1911. Page 1275
