Jap engine dating
In wartime Air Ministry documents, the Alco Featherweight engine is referred to as a 'J. This hole provides the necessary clearance for a BTH mag's longer body (see picture above).
Despite that, the vast majority of these engines actually left the factory with the more compact Wico mag - hence the characteristic gaping hole at the rear.
In fact they look rather like a big JAP bike engine that's been shrunk down, or built as a half-size scale model.
They certainly show their road-engine heritage in a way that no other JAP stationary engine does.
They also went all over the world with the various forces and can therefore turn up anywhere.
Fastenings are an odd mixture of Whitworth/BSF and AF - perhaps a consequence of multiple standards after the Americans came into the war.
The two 129cc, OHV engines shown below are branded 'ALCO' and were marketed by Arthur Lyon & Co. They were coupled with various items of equipment as power units for use by British forces - principally battery chargers and fuel pumps.
Ex-charger engines show evidence of four studs fitted in the rear cowl to which the charger's dynamo flange was bolted with butterfly nuts.
I'll add any info I can find to this page as things progress, so hopefully it should become a useful resource for other owners.
Note that this version of the JAP OHV Model 3 was replaced by a totally different 150cc side-valve Model 3 soon after the end of the war (see below), which can cause confusion when the engine is being discussed or spare parts searched for.
The first engine on the left is an ex-generator power unit and that on the right was fitted with a flat belt pulley as original equipment - probably mounted with a pump alongside as part of a mobile refueling rig on an RAF base.
Both engines have all-alloy cases and cowls and both have patches of khaki paint present as clues to their original owners.
The JAP Model 3 and the war The JAP Model 3 was clearly a wartime concept, designed down to a very simple spec and budget, using light alloy wherever possible for low weight and portability, but also capable of being manufactured from whatever metal was available at different times during the war. Notice also the captive, folding starting handle - so it won't get lost when the unit is moved around a site or thrown in the back of a truck.