So the George Jetson whine in the Xii is apparently inherent in all these bikes due to the straight cut OD gear and the output bevel gear set. Durable yes, but geez how annoying.
As I finished rebuilding my '97 this spring, the mornings were still cool out, so I checked the table in the owner's manual and dutifully filled it with dino 10W-40. After a few test runs around the neighborhood everything checked out and I was off.
I soon realized that as the spring wore on and I took it for longer rides, the temps in the days naturally got hotter, and as my engine temp climbed into the afternoon, the whine from the OD gear got more and more pronounced; and at anything over 80F outside, resonated incredibly loudly at a perfect 56mph in my helmet, giving me severe headaches.
This was not what I spent 6 months rebuilding a Voyager for!!!
I also noticed that the engine was generally just very clackity (is that a word?), like a old dried-out sewing machine; but there's a lot going on inside the engine with all the chains, gears and 4-valve head, so I expected about as much.
One day in early summer, I saw a Lucas product in the store that claimed to quiet geartrain and valve clatter. A little internet research yielded that it was likely a heavier weight oil with a lot of tackifier thrown in for good measure (ever seen their display with the little gears and handle?). Given the wet clutch, I shied away, but it did get me thinking; the owner's manual had a table of oils listed....
Another look at the manual left me realistically with 2 choices 10W-40 or 20W-50, basically a viscosity grade difference at running temp and cold start. Knowing that synthetic oils generally hold a desired viscosity curve thru temperature change better than dino oils, I selected a good quality synthetic 20W-50.
Immediately the engine was markedly quieter at idle and under load. The transmission whine was also toned down to an acceptable level (it'll never go away), to where it doesn't have such a sharp resonance at speed, and doesn't give me a headache.
One interesting side effect that happened is that the engine immediately started running a couple of clicks cooler on the needle. I've never seen this happen with a water-cooled engine before, though I have when playing around with industrial gear-drives and different gear-oil viscosities in them. I've asked around the professional lube engineers that I know, and we can only figure that basically lubricity (lubricity-->friction-->heat) in this particular engine is better due to the viscosity change. The fresh top-end engine rebuild could also make this temp change just all coincidence too, as the engine is wearing in and still loosening up.
Regardless, I'm very pleased. I can now ride the bike comfortably with George Jetson quietly reminding me in the background of my Saturday mornings in front of a Quasar in the 1970's. The only downside is that I'll have to watch cooler ambient temps in the mornings during late-fall and early-spring rides.
A lot of guys on this (and other) forums use 15W-40 Diesel-grade oil, due to the extra wear and soot-carrying additive package, compared with gasoline oils. This is a good choice and the 15W would be a good compromise between 10W & 20W for cooler startup temps. On the high-temperature end though, I will have to try it to see on my particular bike if the -40 side of it thins out too much in hotter temps and recreates the sharp resonate whine that the 10W-40 did.
