As a Ken I felt obliged to respond. Not being a reader of Porn I have not read this from Ken Follet.... by searching the web found this on the car.
https://nationalmotormuseum.org.uk/vehicle-collection/morris-cowley-bullnose/https://classicandsportscar.ltd.uk/...-2-seater-with-dickey/classic-cars-sold/62365The Side-valve engine was the precursor of the Overhead valve engine. - The configuration used mostly today.
Overhead valve engines use valves mounted in the cylinder head, along with the ports for inlet and exhaust and valve gear to operate the valves, This needs a mechanical drive from crankshaft to cylinder head to operate the valve gear.
Earlier engines were much simpler.
The valves were on the side of the engine cylinders. Hence Side Valve.
https://en.m.wikipedia.org/wiki/File:Side-valve_engine_with_Ricardo's_turbulent_head_01.pngView attachment 150389
The camshaft was at the bottom of the engine, next to the crankshaft, and drove valves that were mounted in the cylinder block directly. The inlet and exhaust ports were in the cylinder block. The passages from valves to cylinder were shaped from the cylinder head and face of cylinder block. The combustion chamber was inevitably a flat thing, not unlike your hand placed flat on a table top with a Vee-formed between your middle fingers. 2 fingers were the passage for inlet, 2 for exhaust.
https://www.google.com/search?q=sid...ient=gws-wiz-serp#vhid=hM6Kmm6w6teLMM&vssid=lThis was a very poor combustion chamber by comparison with the more complicated overhead valve engine.
https://www.google.com/search?q=ove...CBgeGA3iAwQYACBBiAYBkAYI&sclient=gws-wiz-serpAn ideal combustion chamber would be spherical at bottom dead centre. - But almost impossible to make!
Hope this helps?
K2