If I find something that works, I tend to keep using it until some problem justifies a re evaluation. I have used Castor R 40 in my gearbox for years and find it excellent. Unlike using it in engines, where if you were travelling far, you might realistically be concerned about carrying or obtaining fresh supplies, the gearbox hardly ever needs topping up.
Castor 40 sticks to the gears and is much less inclined to be flung off than mineral oils. The thicker film is very suitable for the large gear teeth and especially the bronze bushes. The bronze bush on the high gear is large in relation to the surface speed of the high gear bush and wear and frictional losses are usual here. Castor 40 certainly reduces gear and bush wear and does not gum up in this application. I prefer to modify the case to fit an oil seal on the high gear sleeve and to put oil grooves in both the high gear bush and the small inner thrust head face of this bush that takes all the reaction loads of the clutch springs when you declutch.
Chlorine based high pressure additives in some mineral oils can attach copper bearing bronze bushes, but it takes some time.
While I am rambling on, I will tell you of something that might be of interest in the future. We have re designed the twin cam clutch release mechanism that I have used for years on my racer, so that it can be manufactured more economically. The traditional type is quite heavy in operation and expensive to make. Its thrust is taken by 1/8″balls having point contact. Our aim is to make a release mech with a needle thrust race and oilseal that is smooth, light and long lasting and affordable. Flywheels. We are often faced with flywheels with damaged tapers so we have made equipment so we can accurately regrind these and recover the flywheels.
I must remind myself that when the sun comes out a little, I must take time to enjoy some riding. I will soon decide which VMCC meetings I will compete at this year, but I am definitely going to the Beezumph in early September. Richard has promised to finish his racer so father and son can have a Scott mounted outing together. I shall not go to the festival of 1000 bikes, as this is for genuine historic machines, wheras mine is a private race special. My favorite toy!
Kindest Regards to all Roger
PS Remove the brass level plug about one inch up the front edge of the box and pour in your chosen oil through the top access hole until it starts to come out of the level hole.
Sources of supply. Try your local dealer but otherwise I get mine from
https://www.suprememotorcycles.co.uk/about.htm
