Clutch switch

[rickm]

Regarding oil, I use bike specific wet clutch fully synthetic without any issues (no clutch slip etc).
I take the line that I want the best most slippery oil I can get to protect my moving parts

Allegedly, I've read tech papers stating if the oil is too SLIPPY, this can damage/wear roller bearings as they can end up sliding, rather then spinning as designed?

Yes, I've seen that too, although it must be difficult to know in a working engine exactly at what point sliding rather than spinning might occur. Guess you'd just have to strip it down and look for abnormal wear?

[warren3200gt]

I would think modern oils are designed for modern engineering tolerances which are a lot tighter now than in the 70's. Those larger 70's gaps need to be filled with something or the fit will be sloppy and wear would be excessive. The viscosity of semi and fully synthetic is thinner than the same grade mineral so, to my mind, wouldn't fill the "gaps" as effectivly or for as long as good ol mineral.
As semi and fully synthetic oils were not around in the 70's our bikes were definately not designed with them in mind so I cant see any reason to use them and have plenty of doubts which makes me not use them.

[Pigford]

Those larger 70's gaps need to be filled with something or the fit will be sloppy and wear would be excessive. The viscosity of semi and fully synthetic is thinner than the same grade mineral so, to my mind, wouldn't fill the "gaps" as effectivly or for as long as good ol mineral.

Banana skins spring to mind

[rickm]

I'm not an oil expert.
I guess my opinion is tainted by my own experience with my first J back in the 80s.
After a sustained high speed motorway run it fried the mineral oil and welded the scraper rings to the pistons. Amazing that it still rode the 60 miles home, albeit with plumes of oil smoke coming out of the exhaust. I don't know whether modern synthetics would fair any better, but I know the old stuff wasn't up to the job. I expect today's mineral oils are probably better than they were back then.