After much fiddling with the fuel and ignition system of my non-running ATCO 22" (there's a great spark that stays lit under compression, and somewhere near the right amount of fuel getting into the cylinder), I decided there was nothing for it but to take a peek inside the engine as while the was a reasonable amount of compression, it wasn't the best I've ever felt. After pulling the cylinder off (with the aid of a wooden dowel down the plug hole to gently persuade the piston out!) It's as I'd suspected, a partially stuck ring, and the grooves were pretty packed-in with coal-like deposits. which made getting the rings past the bottom of the cylinder require the dowel treatment! nothing harmed or broken, and i'm confident i can get her to make some compression again! It's the bottom-end that worries me!
There was enough slack in the conrod (both ends) to warrant splitting the crank for a proper inspection, it seems that the Little-end bush was installed incorrectly with the oil-hole misaligned (or maybe it spun in service?) but I'm happy to make one of those up and take up any wear, at least the gudgeon-pin is unworn!
The Big-end is the problem though, there's some nasty wash-boarding on both the crank-pin and conrod, the crank-pin being the worse of the two. It looks like I may have to regrind my crank-pin and hone out the conrod to suit some oversize rollers (hopefully i can find something suitable). Alternatively, Steve at VS stocks a 2 thou oversize crankpin but that would not solve the problem with the rod.
Does anybody have any other recommendations? I'm a reasonably competent machininst that's not afraid of a challenge!