Hum, Tony, the earlier bikes needed much more maintenance to clean the engine's internal often.
And this is a PITA.
i am not sure I understand what general maintenance requirements you think applied to a /5 or a /6 that do not apply equally to a /7 or a R65. In any event, the oil technology changes over the period of time from a /5 to now would well and properly level that playing field.
To explain, my friend Bill bought a basket case Norton Atlas (750 precursor to the Commando in a Featherbed frame) in about 1985 and then over a period of several years restored it.
In 1989 Bill announced that he was going to ride the Norton to Phillip Is to watch the races. now Bill is a 1st class and very clever mechanic, but I'd watched him screw that Norton engine back together and I knew that nothing particularly special went into it. i also knew that back in the day (circa 1968), no Norton Atlas ever went much more than 3,000 miles without going "bang", there were simply fundamental design flaws in the oiling system for a start. i also knew that Bill's engine had not been apart in the previous years that he had been riding it post restoration so I very confidently bet him that he had no chance of getting to Phillip Is, much less getting there and back.
The parameters of the bet were that normal services work was OK, but anything deeper than that, meant he lost.
I rode with him to mid NSW, a distance of about 2500lm or thereabouts (and a little over half way to Phillip Is) but had to return for work purposes.
To my annoyance I kept getting phone calls from Bill telling me he was in Sydney, then further south and finally at PI. When the races finished he set sail back to Townsville arriving just on 4 days later, the Norton running like a Waterbury watch.
when it came time to settle up I begged him to tell me what magic he had performed that the Norton factory couldn't master 30 years previously. Bill asked me - "what is the single area of internal combustion technology that has had the greatest advance in the past 30 years?"
The penny dropped - OIL. That was why the Atlas engine could live in 1989 and could not in 1968, modern engine oil, detergent additives, chemical packs to allow the oil to absorb and carry chemical combustion by-products, friction modifiers and viscosity stability said it all.
For that reason alone I am confident that an R50 or an R60 in the here and now would prove a better long distance tourer than the R65 - now that is not a criticism of the R65 but the r50 and R60s were designed to comfortably cover long distances, heavily loaded over indifferent roads. With the greatest of respect to you, the r65 was not.
As a further comment - improved oil is the reason my R100RS has lived so long, i never got around to fitting it with an oil cooler, but I do have a oil thermometer dipstick. Traveling around the northern part of Australia i have frequently seen long term oil temps exceeding 130 degrees Celsius. I suggest to you that conventional 50/60/70s wisdom says that engine oil begins to break down and fail at sustained temperatures in excess of 120 degrees Celsius. Now I have always run good quality oil and changed the oil when due and run 20W60 in summer and 15W50 during what passes for our winter, but I do think that had the oil not been vastly superior to what was around when /5/6/7s were new it would not still be running almost 40 years after it was manufactured.
