Sure is an expensive hobby for some of these bikes with limited parts resources, Although super cool you can still source OEM/NOS parts. 650 Triumph, unit BSA 650 and some others are a fraction of that cost. It aint cheap on some of these less common machines.
I noticed that some of my pistons as well as those in the links above are slotted. In NOTRUN world every resource I know of strongly condemns this design and pistons known to break across that part. Certainly a 500cc preunit BSA twin does not stress the pistons as much as Norton/Notrun twin but I wonder if that happens with many BSAs?? Not an issue?
I had a guy over this weekend I was sourcing some parts for and he was complaining about old motorcycle parts prices, He just completed a restoration of a 67 Mustang and was starting a early 1960s Chev V8 hot rod project, in comparison, One of my favorite vendors offers this for $374.99 USD (Economies of scale).
My wife has a 1969 Chevelle project, Virtually every part is made new reproduction and multiple vendor choices..Ongoing project but wife says I need to sell some more motorcycles, The Mrs wants to order parts..
See:
http://www.northernautoparts.com/ProductDetail.cfm?ProductId=2921" Chevy 350 Complete Street Performance Engine Kits
Master Kit Includes:
Speed Pro Performance Camshaft
Speed Pro Lifters
Cloyess Performance Timing set
Speed Pro Pistons
Moly Piston Rings
Clevite 77 Rod Bearings
Clevite 77 Main Bearings
Clevite Cam Bearings
Melling Hi volume Oil Pump
Steel Frost Plugs
Fel Pro Gasket Set"
SBC CAST pistons are super cheap and typically start at $11.00 each,,
But even Performance regulars are pretty inexpensive,,
See:
http://www.northernautoparts.com/ProductDetail.cfm?ProductId=2126" Speed Pro Pistons DUROSHIELD® skirt coating dramatically reduces friction and related scuffing without the need to adjust wall clearance. The result is enhanced ring seal, increased horsepower and extended piston life.
Speed-Pro’s hypereutectic pistons operate perfectly with standard ring end gaps and have conventional ring land locations. When compared to traditional cast pistons, which are not designed for performance use, the hypereutectics are significantly stronger, particularly in the highly loaded ring land, skirt and pin bore areas. Speed-Pro’s FM244 Alloy contains 16.5 percent silicon and has excellent tensile and fatigue strength. This material’s improved thermal characteristics, its greater hardness and the increased resistance to scuffing permit tight bore clearances which help minimize noise on cold engine start up. This quiet operation, along with a lower cost are the primary advantages over a comparable forged piston. These pistons are an excellent choice for street performance, “claimer” oval track engines and bracket racing use. Speed Pro pistons will also work well in moderate supercharged applications and are suitable for towing and marine use"
Ford and Chrysler applications are much higher costs which is why SBC are the most common choice for hot rods...
Some piston applications you can find a auto or other Motorcycle application that can be adapted which is common in 2 strokes, but I dont think you can find any application for a A7..
Sorry to hijack your thread, just musing on the relative issues of cost between projects.