Originally Posted by DaveInIreland
I have a pair of 30 year old Universal Japanese Motorcycles, and can say with some certainty that changing to synthetic to get the 5W grade at the bottom end paid dividends in eliminating cold clutch drag and it also lets the engine rev more freely, of that I'm sure.
Butt dyno says it's a little bit better, but who knows - these things are totally subjective and I could be feeling something that I'm looking for.
The other benefits of synthetic in an air-cooled engine; greater resistance to heat breakdown and (hopefully) shear resistance will make themselves known in the next few months. This is my first fill of synthetic and I'm waiting to see how it pans out.
Currently I'm running a diy blend of 1L 5W/50 Champion Race Synth (to get some of the extra ZDDP) and 2L 5W/40 Pennasol (re-branded as Lidl synth) and according to this, I have a viscosity of 97cSt
http://www.lubebase.com/cgi-bin/graph/calculate-blending-vg?desired_vg=97&visc1=88&visc2=118
The overall result is pleasing; no cold clutch grab and gearchanges are nice and smooth, although the quality of gearchange might deteriorate as the oil ages. Clutch slip, while not totally absent, only shows when provoked and isn't a problem, as such.
Thought I'd just update that above.
The clutchslip became a little mor frequent over the next few thousand miles, but never enough to prompt me to replace it. I eventually replaced the clutch as a clean-sweep when I had the top end and barrels off to refresh the top and fix an inevitable bottom-gasket base leak the GS850 Suzukis all suffer from.
On examining the old clutch and springs, there was nothing wrong with the plates, save a bit of glazing - no discernable wear thin-ness but the springs were all weak. Standard factory springs from 1980. I replaced with new plates and a mix of 3 HD and 3 new factory springs, and it's now perfect. The old clutch had done at least 80K miles and likely a lot more.
I'm sure if I de-glazed the old plates they'd probably do fine in another engine used purely as a second-line bike.