Jase, Happy to run through what I have done, in various stages.
I have had the bike 14 years. It was on +40s with the part number of old (which i've forgotten, but whatever was the norm back then, Swarfy etc know these things!).
After about 30,000m with me - and dunno how many if any before - I had the engine down, to deal with an end float increase on the crank.
While I was there - or at least I think it was the same visit, I only make very rare ones inside the A! - I replaced the rings, which were showing wear (oh, and exhaust valves and guides while I was on). I also replaced the big end shells while the crank was out - no wear at all there, nor on the timing side journal / bush which showed 1.5 thou clearance and was therefore good. But new shells, why not?
The cylinders themselves were also excellent still, but the pistons were showing some signs, with skirt clearances getting towards the end. No scuffs, no nasties, just a bit of wear. Wanting to get every usable mile out of what were a good pair (because I'm a mean swine and also like bits that have run togeher to keep doing it as long as possible), I decided on 'rings only' for the time being.
After another 15K the engine was starting to get a tad noisy hot. Oil consumption modest - noticeable yes, but no smoke. Inlet valves had been excellent when checked, so I assumed probably 'Nothing to See There' then.
So, knowing the pistons were tired last time in, after 5000 more miles I decided to see what was what. Most noise seemed to be coming from the timing cover, but all the usual suspects in there were in correct shape, and I'm belt drive on the dyn. No flop on breather, good ATD. Some possible wear on intermediate gear / cam pinion / whatever due to mileage, but nothing bad and nothing I could compare it to as I only have the one A10.
In discussing matters with Beezermacc, who knows a thing or two and does some of the same things I do, he reckoned that although the noise might mostly seem to be coming from the timing cover, the odds were that the pistons were starting to clack about after such a mileage, and that iron head engines can apparently refer noise from pistons all over the place. Which of course tallied with where I was myself.
So apart it came.
Bores still excellent with a max wear of under 3 thou, and mostly at between 1.5 and 2, which I'm perfectly OK with. No ridge at top, no marks or funnies. As I don't want a rebore unless and until I really have to go to +60, I'd have put up with a couple of thou worse if I'd had to probably! But the pistons were now down 8 thou on skirt diameters, using the excellent data available on here for them. That was 3 thou worse than when I'd decided to keep them for the time being, so on a downhill slope, and probably accelerating towards the buffers..
The conrod eyes remained spot on for size, parallelism etc, no problems there. Head bits all still good. Even the sparking plugs, the same pair have done nearly every one of the miles I have done - B6HS NGKs - looking good for a few more years.
So it was clearly a case of 'just pistons' and nothing else.
IMDs had been recommended on here by several people, and are easily available at 7.25:1 . . . so that's what I got. +40s again.
They fitted with good skirt clearance, both cylinders, thrust faces and other sides, and no rock at tdc. Rings pre-fitted, and no need to check them, the makers' tell us. Modern oil ring looks the business.
Didn't even attack the bores with a hone, as I'm not convinced about that stuff unless things are obviously heavily glazed. New pins were a correct fit in the rods - bit of warmth, usual thing, to get everything in place - and then the only hassle: the bloody awful circlip design, with no eyes or tangs to grab, and powerful little sods they are to squeeze too. Anyway, sorted with cursing.
Bike started first go, no smoke. Most noise gone when hot, silent cold pretty well. Oil consumption back down to 'norralot if anything' from 'bit more than I like'. Still running it gently, although without a rebore no need to be too careful I suppose. Solid copper head gasket. Checked torque (I go 34ft lbs on iron) after 200 miles, and nothing had moved at all. Brian from Oz told me they wouldn't have moved, but paranoia ruled! Rockerbox needed a tad more spannering on the four downward facing studs at the corners. Oil feed pipe banjos not leaking.
On the road, slight vibes in the 45-50mph area in top which used to be elsewhere, but not a nuisance. When I've done a few more miles it'll be back to 55-65mph at all times, where it's always been happy. And here's hoping the IMDs do as well as the old jobs, on a bike that has really been ridiculously reliable on a diet of fairly modest maintenance. I have been very lucky! Or maybe, you just can't beat the combination of LJ crank, thick-flange barrels, low compression and an iron head with the larger inlet and a 389 carb. It's supposed to be an SR according to the paperwork, but it very isn't, obviously.