Having recently re-discovered the delights of small diesel engines, after an interval of 45+ years, I wanted to acquire (among others !) a Mills .75, being my first love, to see perhaps if, this time around, I could actually get something to fly reliably (with r/c?) under it's power (I use the term loosely). I actually ended up with two examples, both as yet new and un-run. I firstly acquired an original Mills but being an absolutely mint example, still in it's original box, etc, I decided at this stage, that it was too precious to use in a model. So, I kept my eyes open for, and duly acquired, an Irvine replica, which I'm told are very practical for 'everyday' use.
Now to my question: Does anyone here have knowledge of the serial numbering used on these engines? My original Mills is numbered 67700 (67 on one lug and 700 on the other, written as 67700 on the factory inspection certificate and guarantee). The Irvine replica has the serial number 02537. Can anyone tell me whether the date of manufacture can be deduced from either serial number, and is my original engine a series 1 or 2 ? - I believe I am right in thinking there were two series but have no idea of the difference between them - perhaps somebody can enlighten me on this as well. Thanks, Alan

Hello; I just checked my Mills. It si an original English version. The serial number is on the inspection certificate, it is 13157. I think it is from '42, at least I have been told that it is.

I don't know if there is any significance to the number.

The Mills 75 Mk1 was introduced in 1948. The crankcase was manufactured from solid and has the angular look that you see in the first photo below. This version is extremely rare to find today.

The Mills 75 Mk2 came onto the market a year or so later and has the cast, more rounded crankcase, like the Irvine replica that you see in the second photo below.

The vast majority of the Irvine Mills 75 replicas are of the later, cast version.
Irvine did also produce a small run of Mills 75 MkI replicas – to confuse matters Irvine calls these engines the Irvine Mills 75 Mk2…..
The last of these had gold anodized heads, see photo 3, below.

The Mills serial numbers are confusing. I have seen them explained somewhere in an article, by P.G.F. Chinn I think it was. Maybe someone else out there can find the reference?

Tomas H.

Many thanks, at least I have the Mk1 / Mk2 question answered. It seems that one could have a significant numbers of engines, not to mention a significant financial investment, by just collecting Mill's .75 variants - but it's not hard to see why this endearing little engine remains so popular.