10W-40 is recommended by Honda when operating in
all temperatures. But not many of us ride in temperatures below zero degrees. Honda France recommended 20W-40, for most of us probably the best choice. A Dutch tribologist who worked for Castrol and published in a magazine for pro's in the automotive field and who owned himself a CB550K3, used 15W-40. That's what I use. I have best results with Castrol 15W-40 which used to be named High Mileage. It helps keeping the rubber seals elastic. How many of you have had to change the shifter seal? Mine leaked a little bit too. Now hardly anymore. Although the package doesn't specify JASO, I don't worry. Here's why.
1) I never had the clutch slip.
2) Break-in period is decades ago.
3) Could well be my oil meets JASO, but Castrol simply choose not to inform you because they have a complete line of 'motorcycle oils' for a higher price. For instance, the Shell Rotella you all love so much overthere, is also sold here under the name Rimula. On the Rotella
package it says: JASO. Not on the
Rimula package here. Does that mean Rimula doesn't meet JASO? We don't know. Could well be Shell
here choose not to inform you, because
here they offer a complete line of 'motorcycle oils' for a higher price. I myself wouldn't go
-50 unless in extreme conditions that I have never met, not in Spain, nor in Greece. BTW, in France it usually gets pretty hot too. Don't aim for a higher oil pressure at all costs. Chance is it will make life harder for your engine as a thicker oil will flow slower. I prefer to have my oil circulate as fast as possibly can, to achieve maximum cooling. Also you want the oil to arrive at the camshaft as quick as possible. That's where the wear takes place, not at the bottom end which is practically indestructible.
Back then Honda choose Castrol. In cold start tests Honda had carried out, Castrol arrived the quickest at the camshaft and so became the winner. But... those tests were done late sixties, early 70s.
