Hello LewisS...The Royal Aircraft Factory air pump (compressor) opperates on the same basic princaples as the " Rotherham " pump fitted to Sopwiths etc ., and I guess you could quite rightly describe them as looking like a model engine ...after all , they have many similar functioning parts .
The RAF type is made with a Gunmetal (bronze ) cast main body , ie. crankcase and integral cylinder , ..this includes the two lugs on either side that you see in the photo .
The forward projecting crankshaft is carried in ball bearings on a steel nose piece...In the photo you can see that the front end of this nose piece supports the front portion of the aluminium fairing .
A bottom plate acts as a removeable sump and is screwed on with 4 set screws ...Between these are the 2 mounting bolt holes , which attach it to the tube support frame , hanging down from the nacelle .
At the " cylinderhead" position , the union for connection to the delivery pipe can be seen as it projects out beyond the top of the ally' fairing .
It is emfersized that the alluminium parts are in the nature of fairing pieces for streamlining purpose only , and serve no function as far as the opperation of the air pump is concerned .
I cannot scan the drawings of the part as they far outsize my A4 scanner , and unfortunately , I have no photos at all of the pump before the fairings were fitted , lacking a decent camera at that time .
( I may be able to do a sketch later , time permitting . )
Regards..John .