Hi Henry,
I was 12/13 when I decided that I wanted to advance from a mamod into the rally sizes. I did a lot of research which eventually came up trumps.
I would fully advise that you go part built if you have access to workshops and are willing to learn a fresh set of skills. If you go part built or do a restoration, you're indefinitely going to lean about the principles of steam engines and you'll learn how a traction engine works as well as learn new engineering skills such as metal working, measuring, machining, fabrication, interpreting drawings and fitting etc. All very adaptable skills that you can take into the workplace if you are interested in entering engineering as an eventual employment option. Also, if you go part built or do a restoration, the things you learn during the project will help with the maintenance and upkeep of the engine when it's finished.
I was 13 when I got my first engine. It was a part built 3" Burrell traction engine bought from Station Road Steam. My grandfather bought it initially as the chances of a 13 year old having enough cash to buy a 3" engine are highly unlikely. So I was doing what I could as often as I could to get the engine finished. I was shown how to competently use lathes, milling machines and various hand tools to produce a quality finish.
It took me around a year and a half to get enough money to buy out a 1/4 share in the engine. A sum of £1200.
So before you do anything, you need to find a suitable engine make and scale. As a mere beginner, I suggest you go simple like I did. So you will be looking at a single cylinder agricultural/general purpose engine in a size that is rally worthy but small enough to be easily transported, used by a beginner and cheap enough for a teenager. A 3" scale single cylinder agricultural/general purpose engine is what you want as a basis.
A few engines fitting this description are:
3" Burrell Agricultural traction engine to Plastow's design- Very popular for beginners of all ages and aspects, castings and drawings supplied by bridport foundry (the engine I started off with)
3" Fowler A7 General Purpose traction engine- A little larger than the Plastow Burrell and more powerful. A bit more powerful and a bit more expensive. Generally a highly rated engine however. Road and rally worthy.
3" Marshall agricultural traction engine- A less common engine but a well designed model and aesthetically pleasing engine.
3" Allchin agricultural traction engine- Becoming more common in this scale although most are built to W J Hughes design in 1 1/2" scale. A very nice engine all round in terms of power and looks. Quite a large engine for the scale
3" "Little Sampson" tractor- A very small engine for the scale but still rally worthy. Bit odd with looks in my opinion. A cost effective solution.
3" Aveling and Porter road tractor- Simple and compact in design. A kit engine from Maxitrak. I've heard a lot of different points of view from this type of engine.
In terms of cost, for a relatively new engine, you're looking at £7,000 to £10,000 depending on what you get and the quality of the build and finish.
For a part built engine, you can't price them unless you know what you get and what needs to be done. As is often the case with part built engines for sale, the boiler isn't there, which is the bulk of the cost in an engine. You need to expect that the chances of a part built engine coming up for sale without needing any machining having to be completed is going to be quite unlikely unless it's a kit engine. With this option though, you are much more likely to get better value for money.
Keep an eye on the Station Road Steam website and Steam Engines for Sale.
I hope some of this helps. I'm also in the South West and am only 16 so if you have any questions just ask.
Thanks,
Dan.