Well for what its worth, during the sixties my BSA was an oil spewing, vibrating piece of junk which would start maybe half the time, sported an Frankenstein electrical system and actually used to shed parts as it proceeded down the highway. My Honda and Yamaha were wonders of smooth reliability and never, ever let me down. Somewhere in that scenario superior technology must have played a role.

The BSA had very cool optics, however.

Normw

For what it's worth .Comparing bikes of the same era and similar engine size and type .

My BSA started every time first kick ,did not leak oil , vibrated like a bugger , looked great [it was an Eddy Dow special but the later Lightnings were good lookers too ] ,went well for a 650 twin and sounded lovely [ Dunstall Decibel silencers ], handled good .Brakes poor .It never let me down .

My Yamaha starts every time first kick or lectric , leaks oil [clutch and countershaft seals -soon to be fixed ] ,vibrates above 85 mph ,looks horrible, slow for a 650 twin but goes better now the engine has been modified ,sounds nice [Commando exhausts] ,handles average .Brakes good .Blew the alternator twice last year and once this year .This bike was very well regarded in it's day and had a long production run .

My Norton starts first kick , leaks oil [ primary case and gearchange o rings - soon to be fixed ] , vibration is not felt [ isolastic engine mounts ] , looks great , goes really well for a supposedly 67 hp bike , sounds fantastic [Dunstalls ] ,handles really well .Brakes only average .Has never let me down other than an exhaust nut coming loose although I suspect the zener diode will need replacing with a solid state reg/rect system .

I haven't included any singles, triples or 4 cylinder bikes as I believe it's important to compare " like with like" and only comment in depth on bikes that I am completely familiar with .Also the bikes are in similar mechanical condition .
Technology : I've had all of these bikes apart and am impressed with the roller bearings in the Yam engine ,but the quality of it's castings is poor and the intake and exhaust ports are badly shaped . The Norton has superb gas flowing qualities and a good combustion chamber shape but alas no OHC and roller big end .

The Japanese bike has a robust engine that can be tweaked to get more power - it needs it . The BSA produces the same power as the Yam but is faster [ raced with my mate who had one ] .The BSA could be tweaked to get more power as well but not as far as the Yam . The Norton is probably as highly tuned as you would want to go .
Frame technology , Norton far superior , BSA second , Yamaha a very distant third .

Riding pleasure : Norton first by a long way ,Yam and BSA about the same .

All of the above bikes could be trounced by a four cylinder bike ten years younger but that would hardly be a fair comparison .
But it would be interesting to compare them to a Kawasaki W650 and a New Bonneville .

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