I was actually referring to the S under the engine number as I have only seen numbers previously eg 0 , 1 , 2 , 3 etc. So what does this engine belong to ?
The significance of the single numeral/letter on the bottom crankcase half isn't known, and it's unlikely we'll ever find that out.
That letter prefix serial number belongs to the Model 5 Series 2 as far as can be worked out, so probably 1958-9 era.
