Wiktionary
side valve
n. (context automotive English) A type of internal combustion engine design which has the inlet and exhaust valves in the cylinder block beside the piston. The cylinder head is then a simple dome extending across the valves and piston.
Usage examples of "side valve".
A large horn, longer than Roger was tall, had been laid upon the walls, obviously in preparation for this moment, and the Gastan first blew into a side valve.