Just had a thought. It might be a good idea to build a list of machines and what size tyres they use. This would give a better idea of how common or not each size is and where tyres are interchangeable. To make a start I have listed a couple on the attached.
Have you tried Tyre-Finder or Micheldever Tyre Services? Tyres are one of those parts that can be a real problem to replace on some machines as many are obsolete sizes eg 3.00-6 (12×3) for Monro Tiller and small Barford Atom.
If I remember correctly the chassis number should be on a brass plate attached to the inside face of the chassis on left hand side (when viewed from rear) below and forward of engine.
One of the later gearbox manuals I have has the name Hi-Ton Transmissions on it, I don’t know if they can help.
Another source maybe one of the vintage motorcycle parts suppliers.
Looking in the parts list for the later type it would appear the clutch is on a keyway but I cannot see how it would come off. Plenty of penetrating fluid (not WD40) and some heat maybe the answer. For the clutch to work the outer needs to be able to slide freely on the shaft.
Not sure if early clutch is the same.
What spark plug do have fitted? If you look on the Green Spark Plug Company website and look up your plug it will give you the hex size.
Suitable tyres can be obtained from motorbike tyre suppliers. The original tyres had a unique tread pattern for the Allen Scythe.
Barford trailers, flat bed or tipping are a bit like hens teeth and rocking horse S~*t. A well known online auction site much used by our members is where I got mine from. The dump trailers are prone to rusting out at the bottom as they fill with water if left outside.
The excellent SIMAR website has some information on the M11, see link.
According to the website this model was produced from 5th April 1930 to 28th April 1936 with serial numbers 3001 to 3098. If only 98 were produced then they were never a common machine.
