Reckon it started life with a big journal crank but see my other post today and I'm maybe not 100% sure.
Service Sheet 207 covers cranks up to 1965, giving regrind specs for main and big end undersizes.
Whatever crank you consider, all will need attention to the oilway between the big ends, the so called sludge trap. Also look for worn splines on the drive side, and if possible the condition of the crank web behind the roller main bearing, this area where the inner race abuts can become hollowed out if the race moves relative to the crank, destroys the shims then starts on the crank.
Timing side left hand thread is fragile, look here for damage by hooligans smacking the end of the thread to drive the crank through the case to remove the timing gear. Wear to the timing side journal is annoying if worn below commercially available replacement bush size, but can be overcome by grinding enough to clean up, then fitting a custom bronze bush, line bored to fit the crank.
Big ends journals can be metal sprayed and reground, but all this costs more than a good used crank. Big journal crank is favoured, but again commands a premium.
Small journal A7 and A10 cranks are similar, (and easily distinguished from the big journal type with its 3 radial bolts). Some sellers don't know what they've got, measuring the stroke tells all as otherwise they are dimensionally identical which has come as a surprise to some buyers.
Smallest undersize NOS shells for small journal that I have come across is 40 thou down. No point in buying one already ground on the lower limit, odd a couple of thou ovality and you're back where you started. Rusty examples are sometimes a better bet, standard size discarded back in the day and emerging 50 years later. As always, you take your chance with ebay...
But before you spend on anything, get a second opinion on how bad the damage is. All cranks are worth saving, and even as it is, there is value for someone.
Swarfy
