Hi, It's been quite a while since I visited here and even longer since posting. When I saw the word 'Hallam' I was intrigued having posted on that subject in the past..
PJ – I went to find that original posting by Alan Worland but see you have already found it so you will have seen not only his engine but the one I experimented with also and realised that it is not the same design as yours.
Looking at your engine I would hazard a guess this is a much earlier design though how much I'm not sure as I have little knowlege of the types produced. The split crank case and those single bolt mounting lugs signal an earlier engine but that's a calculated guess. The head design is typical Hallam however. If you can remove the head and measure the bore and stroke it will give you an idea of the capacity. Alan's engine and 'mine' are definitely the 9cc versions. It's been quite a while since doing anything with it but if I remember correctly the 9cc version was available both as a set of castings for home machining and a finished engine around 1947-9. I think you will find they were primarily aimed at the model aircraft and tethered car side of things which were very popular at the time.
Air cooled engines can and indeed were used in boats usually with the engine exposed to the elements – so It does not neccessarily mean your engine was not used as such. I agree with the opinion though that the cracnkshaft has been shortened – or the flywheel is too wide for the length of shaft .
Hallam engines were – apparently – not well known for their running properties, something Alan and I found.
I was kindly sent an original drawing of the 9cc version and though I can't remember exactly what it was I do remember finding something slightly awry with the timing as drawn. It was my intention to build one from solid to try to improve it's running qualities as I have yet to make a spark ignition engine but other engines have got in the way so far. All the parts are still here on permanent loan though so maybe some time soon.
Whatever plans you have for yours – I hope it runs okay fo you
One last thing – if you go on the web site 'On The Wire' you may, via that, be able to contact a Hugh Blowers who is very knowlegeable about Hallam engines( Hugh was one of the guys I spoke to about Alan's engine) – I'm sure he would like to hear of yours.
Regards – Ramon