I think you've given those of us with more than one marque a great opportunity to unload all sorts of thoughts! So thanks, I will! And Hat Off to you by the way for keeping your machines running in a very difficult part of the world, everything I ever heard has said it is very hard to do.
Never owned a Triumph, so can't comment too much there, although I've done a few engines of the 5T / 6T 1950s sort for friends. Yup, can be a bit leaky, and sometimes noisy - but not sure it's the two cams that cause it. Nice to play with, although the ones with white metal big ends need to be sent somewhere good to be sorted - and there aren't that many places . . . I think they can be converted to shell bearings maybe, but never had to go there. Same old question of plain bush on the timing side on period Triumphs as on Beesas - but I have never seen too much trouble arising from that, and my own A10 has lasted very well in that area.
Norton twins I know a bit more about, but 60s not 50s in my case. Quite like them, but hard to work on the top end with the engine in the frame of a Featherbed - horrible horrible job getting the head on and off with the pushrods having to be stuffed right up inside it past the rockers to get enough room to drop them down the barrel. Makes an A10 rocker box a pleasure! Chains for cam and sparks are OK I think, and I like the outrigger bush in the timing case, even if it makes assembly a fraction harder. The thinnzer rear chain on many models doesn't seem to have been a big issue either. In 650cc form, they are pretty long stroke for a supposedly sporty bike though - 68mm bores on a 650 is a bit vintage I reckon, what with an 89mm stroke! Even the A10 managed 70mm on what's not a very sporty design, and the Thunderbird was 71mm from memory. The Atlas got to 73mm with the 89mm stroke, which ought to have been more like but actually vibrated a lot due to being at the limit of the design I suppose. Post-1950s though, so doesn't count!
You can see from this I prefer squarer engines, which is maybe why I like another make - the Matchless / AJS twins, which run 72mm with a 79mm stroke at 650. and 72x73mm at 600 - far more like! I also like engines where oil delivery is contrived to be equal in flow and pressure at the two big end journals, and I don't like having to shim crankshafts for lateral movement very much. Another reason I like the AMCs, where that is controlled by standard thrust washers next to the central plain, 3rd, main bearing. And no, they don't break crankshafts every 5 minutes, despite bar room myths to the contrary! No external oil pipe plumbing AT ALL on them either, except from tank to engine. Two cams, pushrods that operate vertically like Triumph, but without leaky tubes . . . Neat design, only marred maybe, like on Royal Oilfields, by the fact that the heads and barrels are separate, which can cause some dribbling on the larger capacity models from round the cylinder base. Through-studs though, from crankcase to head, as per Sunbeams of the vintage area and a lot of other well-designed engines.
You say Nortons love the bendy bits - and they do. But the swing-arm Beesas aren't far behind I don't think, except perhaps in the fork department. I can't do much on my Dominator I can't do on my A10 - and both are more fun on bends than any period Triumph, AMC or Oilfield twin.
As to what sounds best . . . have to be careful here, as noise isn't everyone's cup of tea. But any A on correct silencers sounds good I think (I have pattern Goldies on mine these days though - not bad I'd say), a Norton on the correct cigar-like Campbell silencers is very pleasant to my ear, and I have to be fair and say I have always liked the sound of most Triumphs. The original style correct megaphones always fitted on Matchless twins make a throaty, not excessive noise too, so do the Burgess silencers used by AJS models in the 50s. Many pattern jobs are a bit tinny compared to the real things, which is why I'd rather see a tatty original set up than a highly polished replacement.
If you ask me 'Which is your favourite machine' - the answer is 'The one I'm on'! They've all got their ups and downs, but as a general breed, just got to love them all. (Well, most of them, anyway . . .)
