As you stated earlier, if the vendor is not publishing withstand temperatures, how would I know (scientifically) that I have surpassed said temperature? What I can tell you, TT, is that recently I have been experiencing some clunky shifting and difficulty finding neutral when the bike is hot.
If you cannot adjust out the dragging clutch, then I'd say to try a different oil. Clunky shifting and extra wear on the shifter parts trying to find neutral and shift gears WILL wear the machine's shift mechanism out faster.
I have attributed this issue to the oil pump, where I believe my small oil leak is coming from (still inconclusive, but very likely).
A small oil leak is not going effect pressures in the system or hinder circulation.
Jezz, I hate to sound like an oil salesman. But, why don't you give Honda's HP4 without moly in 10w40 a try? It certainly won't hurt the engine. And I've experienced at least 4 Cb550 Hondas, stop or severely reduce dragging the clutch and make shifting much easier. At worst, you just spent an extra $10-20 on an experiment. At best, it'll make you a happy rider. If it weren't for the cost, I'd go to full synthetic all the time. But, I don't believe the oil change interval can be extended in these motorcycles.
It is not very often that I ride in the city as I do not find the stop-and-go to be enjoyable. Therefore, based on your earlier post, I assume oil can be spoiled on one ride if the temperature of the bike and environment are hot enough. This is all quite fascinating to me and I really appreciate you taking the time to school me.
Yes, it only takes one excursion into high temps to damage oil. It can be a death spiral is some instances. Heat damages oil, oil stops lubricating, parts get hotter, cooking oil more, etc., leading to a cooked engine.
Cheers,
