Abstract: A chain-type door lock comprising a wall bracket, door bracket and a connecting linkage is disclosed. The wall bracket comprises an L-shaped mounting plate which can be secured to the side face of a door jamb by screws and a cover plate which is mountable over the mounting plate to block access to the screws. The connecting linkage is preferably a chain which is attached at one end to one of the door or wall brackets and which has a key at its other end for engaging a slot in the other of the door or wall brackets. The slot may be vertical or horizontal.

Abstract: An air control valve (20, 21) is coupled to the minimum volume region of each cylinder (11, 12) in an internal combustion engine. The open interval of the valves during each engine cycle is controlled responsive to the throttle (FIG. 2) to equalize the air-fuel ratio. The clearance of the pistons is also adjusted responsive to the throttle (FIGS. 3A and 4A) to equalize the compression pressure during engine operation. Specifically, in an engine with two cylinders each having opposing pistons, the coupling systems between the piston rods and the crankshaft exhibit diagonal symmetry (FIG. 1).