MORE than once criticisms have been heard owing to the fact that the makers of the A.J.S have repeatedly won the Tourist Trophy Race with an overhead valve model which was not available on the open market.
Nevertheless the manufacturers acted wisely, for they felt that until the experimental machines had been reduced to a form in which they were safe in the hands of the public it was better not to sell them broadcast. Now, however, the latest developments render the o.h.v. model as available as the popular side valve type.
At the forthcoming Olympia Show there will be staged a super sports model with an engine based on the T.T. A.J.S. machine. The overhead valve mechanism will be almost exactly similar, except for the fact that somewhat longer valve guides are employed so as to reduce wear at this vital point. These valves give a clear port opening equivalent to l^in. and a lift of -fein. They are operated through hollow push rods with an independent return spring for the rocker gear. Recent modifications include an increased head cooling area with vertical fins arranged to lie in the same direction as t he main air current. The detachable head is held down by a round section steel strap semi-circular in form. As might be expected, the head and cylinder joint are formed on the patented A.J.S. lines
Another innovation since the Tourist Trophy races takes the form of an aluminium piston, though the four very narrow rings above the gudgeon pin are retained. A hollow gudgeon pin is fixed in the piston bosses by means of a split pin. a bronze bush being fitted to the small end of the connecting rod; the connecting rod itself is a nickel chrome forging, heat treated and machined all over. The section of the road is extraordinarily light, being no more than il6-in. thick in the web; in spite of this, no trouble has ever been experienced with it. Two rows of ?ftin. rollers aro employed for the big end, an outer race iieing pressed into the rod. The boro and stroke remain as before, 74x81 mm. (349 c.c.).
Plain splash lubrication is relied upon for tho bronze main bearings. On tho driving side of tho crankshaft a standard spring loaded cam type of shock absorber is fitted, transmission following standard A.J.S. lines through a close ratio gear box, tho ratios supplied being 5 to 1, 6.1 to 1, and 9.4 to 1.
For the benefit of sporting riders who desire to enter speed events and liill-climbs, the rear mudguard and carrier have been made in a quickly detachable form. There is also a stay from the saddle tube to the rear of the cylinder head.
This overhead valve model does not replace the standard side-by-side valve machine, which will be listed as before, but with 650 x 65 mm. tyres, modified handle-bars and a much improved front mudguard which, in addition to being splayed at the rear, is formed with inud-trapping channels round the edge of the valances, and a shield at the front to prevent the ingress of air, which usually blows back mud spray on to the rider.
An aluminium piston is also fitted to this model.
Such features as the adjustable footrests, neat knee grips fixed direct to the lank, the spring loaded hand oil pump, are of course retained, and the machine is finished as well as ever.
Modifications to the 799 c.c. A.J.S. passenger outfit consist of aluminium pistons, a similar but enlarged type of mudguard to that employed on the standard 349 c.c: model, the fitting of Lucas Magdyno and lamps as standard, and the arrangement of the change speed lever and switchbox further forward on the tank, so that they clear the rider's knee with comfort.