Here's an intriguing little sideport diesel which came to me from an Australian source. It’s pretty clear what this is – someone’s rendition of a Mills sideport model built around an aluminium alloy main casting as opposed to the magnesium original. The crankcase casting was produced from a permanent mold.

This engine follows the basic Mills design in all respects apart from the bore and stroke dimensions, which have been altered quite significantly to bring this engine far closer to "square" internal geometry - the bore has been increased from 8.38 mm to 9.80 mm. while the stroke has been massively reduced from 13.21 mm to 10.00 mm, giving a very slightly increased displacement of 0.754 cc as opposed to the Mills' 0.729 cc. All components appear to have been made by whoever came up with this engine – no Mills components are used anywhere. Despite its somewhat rough exterior, the engine is beautifully finished and fitted where it counts – inside. Whoever made it knew what he was doing! The engine is a one or two-flick starter and runs really well. 

The big question is - who made it? Could it be a prototype of a proposed look-alike series that never got off the ground? The fact that the main casting was produced by gravity casting in a permanent mold certainly suggests an intention to produce a number of these engines – few home-builders would go to the trouble of creating a permanent mold for a one-off. Given the source, I’d guess an Australian or New Zealand origin, but there’s no certainty. Can anyone out there shed any light on this engine’s origin?