Le Vack’s Legacy: JAP Overhead Camshaft Engines, 1922-25
While it may, on first appearances, seem to be concentrating on a very narrow period of time, the reviewer sees the just-published Le Vack’s Legacy as appealing to the enthusiast or researcher keen to acquire detailed information on engine design right across the veteran and vintage periods up to the present day. This could include the spectrum of car, motorcycle and aero engines, with the Tottenhambased company of J A Prestwich serving both latter categories. Indeed, it seems to have been the largest supplier of proprietary motorcycle engines in the world in the 1920s.
While the range included hardworking and utilitarian side-valves right from around 1907, the company also had a strong presence in competition, including racing and record-breaking attempts. The company’s designer, Valentine Page, was given free rein to experiment with designing and building a small number of double overhead camshaft single-cylinder units, but less than 20 seem to have been made between 1922 and 1925 and it was never the intention to begin series production. Rather, the objective was to learn about the viability of such pioneering designs and achieve good publicity. But
JAP did allow frame manufacturers, plus rider/tuners, primarily its own Herbert le Vack, to put the engines in bikes and race them. They could – and did – successfully address a variety of speed records with these 245cc and 344cc single-cylinder engines, as is documented in this book. (There was also a single 424cc unit employing a longer stroke.)
Author Brian Thorby makes mention of Page and le Vack studying the legendary 1912
Grand Prix Peugeot car engine, designed by Ernest Henry, and which, employing double overhead camshafts, four valves per cylinder at an included angle of 90 degrees, and hemispherical combustion chambers, turned Grand Prix racing on its head. Inspiration for Page seems to have been taken from this power unit and the 1913-14 Peugeot parallel twin 500cc racing motorbike engine, also designed by Henry and using double overhead camshafts.
There are a few minor criticisms; Roger Maughfling's surname becomes ‘Maughling’ and the author also seems to have described the original Henry 1912 Peugeot car engine design as having parallel valves, when the engine pioneered the classic twin ohc hemi-head design in all of its respects, including a 90-degree relative valve angle. Thorby also appears to lack familiarity with the Royal Automobile Club’s car road tax formula based solely on collective bore diameter and infers that it applied in Britain to motorcycles as well. Motorcycles only ever used one of two consecutive arbitrary systems loosely based upon total capacity. Valentine Page also comes a poor second when it comes to credit, behind le Vack? Of course, the frequently overlooked, tremendously competent and versatile Page went on to design many hugely successful and diverse engines such as the Ariel Red Hunter and derivatives, BSA B-Series singles, and, in the last years of his long career, the radically new Ariel Arrow and Leader two-strokes.
Much of the later part of the book is taken up describing the fate of the engines in their later lives, and is extremely thoroughly researched and well-described, complete with some good pictures.
Brian Thorby himself has built at least one engine to running condition, and most engines appear to have survived.
Despite a few minor niggles, I heartily recommend this book in terms of its engineering emphasis, coverage of previously overlooked material and diligent research. Le Vack’s Legacy is published by Banovallum Books. RRP £40. ISBN 978-1-911658-78-8.