OVERHEAD VALVES

King Country Chronicle, Volume XXXIII, Issue 4802, 26 June 1939, Page 6

OVERHEAD VALVES

WHAT EXHIBITIONS SHOW. English motor exhibitions this year did not indicate any notable developments in the way of valve gear, either of unorthodox type or change from overhead to side valves, and vice versa, says a writer in the Motor. This is a state of affairs which will not, I believe, hold good for 1940 models. I think a large number of models for that year will be o.h.v. equipped.

The relative merits of the two designs, it must be admitted, are fairly evenly balanced. One can obtain more power per litre from the overhead valve engine, but its cost per litre is higher. There are many who believe that the cheapest way of purchasing horsepower is to obtain it with the assistance of an L-head, possibly cast in a light alloy. This Is generally infeasable with o.h.v. engines, as one has to make provision for inserted valve guides and valve seats, which is an expensive operation.

The trend to o.h.v. will be accelerated for the essentially practical reason that valve adjustments become a good deal more accessible. This point is appreciated in particular with the modern type of wing structure and forward-mounted engine. Additionally higher r.p.m. is obtained and a greater control over the shape of combustion space without loss of volumetric efficiency.