577,207. Two-stroke engines; valves. POTTON, J. C., PARKER, P. J., and HUNT, R. J. Nov. 6, 1944, No. 19331/43. [Classes 7 (ii) and 7 (vi)] In a two-stroke internal-combustion engine gas or air compressed by the underside of the piston is transferred to a chamber 17b within the piston and conveyed to the combustion end of the cylinder where it is transferred to the combustion chamber through passages in an annular ring 19 controlled by a short sleeve valve 9. In one form, a horizontally opposed twin cylinder engine, Fig. 3, comprises two similar crank-case sections bolted together at flanges 27a and provided also with lugs 27b which may be bolted to a base. The main shaft 31 and shaft 45 driving auxiliaries are mounted in roller-bearings 42 and ball-bearings 44 respectively and carry fly-wheel portions 30, 29, the crank-pin being integral with the part 29 and secured by a nut 46 to part 30. The pin runs in a block 28 moving in a slot in the common piston rod 24. Cams 43 on the main shaft act through push-rods to reciprocate the sleeve valve 9. Each cylinder 17 secured to the crank case is fitted with a two part-head comprising an inner portion 1 and an outer portion 8 enclosing the valve 9 and provided with ports 8b leading to an exhaust space enclosed by a short tube 10 and leading to a manifold 11. The upper end of the cylinder receives a charge transfer ring 19 which has a V-shaped top edge adapted to coact with a corresponding formation on the member 9. The ring 19 has a peripheral groove and a number of radial holes 19d. A number of holes 19a connect the upper V- edge of the ring 19 with the peripheral groove. The inner part of the head has water spaces 1a and is fitted with a part 2 which provides a concave topped combustion chamber and is screwed to receive the spark plug 3. The piston comprises an upper portion 12 secured with limited float by means of a headed member 13 to the piston rod 24. A second piston portion 22 can reciprocate freely on the piston-rod between limits determined by the upper piston and by a washer 23, providing a space 17b of variable volume between the pistons. The portion 22 is fitted with a disc valve 14 which closes ports 23 leading to the space 17a. The lower end of the cylinder is seated in a member 26 fitted with the piston-rod bush 32 and with a disc valve 18 leading to an inlet passage 27h to which the carburetter is attached. In operation, considering first the space beneath the pistons on the upward stroke a charge is drawn in past the disc valve 18. On the succeeding down stroke the valve 18 is closed but the piston portion 22 is free to slide upwards and reduce the space 17b which by the opening of valve 14 will be charged at the same pressure as that in the space 17b. As the pistons approach bottom dead centre the inertia of piston 22 causes the space 17b to be increased again and most of the compressed charge passes into this space. On the next upward stroke the charge is carried in the space 17b which is further reduced in volume by the inertia of the part 22 near the top dead centre. At this point the charge is transferred to the combustion chamber through ports 19a. Meanwhile another charge has been drawn into space 17a for transfer to space 17b on the next downward stroke. The transferred charge is fired by the plug 3 near top dead centre after closing of the inlet ports 19a thus producing the power stroke. Near the bottom of the stroke the valve 9 is raised to open the exhaust passages 8b, these passages remaining open until just before the next charge is admitted from the chamber 17b. In a modification, Fig. 9, for diesel operation the spark plug is replaced by a fuel injector 52 and the exhaust transfer valve is operated by rods 57 through a Y-shaped overhead rocker and an external push rod. The inner cylinder head is recessed to form a combustion chamber 53b which is entered by a piston extension 61 which screws into the piston-rod and retains the main piston 62 without preventing a limited amount of float of the main piston on its rod. A second piston part 64 is movable on the main piston to an extent limited'by a ring 83 and has apertures 64a closable by a valve disc 65. The compressed air between the piston portions is transferred to the combustion chamber by way of ports 64b, 62a and passages in the insert 84. The cylinder and outer head portion are integral. The disc valve 78 controlling air supply to the cylinder is mechanically operated by cams which may be attached to the peripheries of the fly wheels 81, 82. In this form following the transfer of air to the combustion space the piston portion 61 enters chamber 53b to increase the compression and ignite the injected fuel. In another modification, air compressed beneath the piston passes through a valve to a compressed air reservoir, from which a charge of air mixed with fuel may be passed to an injector and into the combustion chamber.