Suitable oils

Hello,
Can anyone advise this relative novice what’s the most suitable oil for the 398cc ABC in
- the gearbox
- the oil tank
Many thanks,
Alan

I contacted Castrol Classic Oils last year re ABC car engines(Trevor Allman autotechenquiries@castrol.com )

They came back with this specification
Engine Castrol XXL 40
Gearbox Castrol ST90
- presume similar for the bike engines?
- I suggest send Trevor an email, he was very helpful.

Many thanks. I’ll do that. I’ll post his response if he says anything different which I doubt.
Alan

The original recommentdation would probably have been for XL SAE30 in winter and XXL SAE40 in summer and that is what I use in my bikes but I use a multigrade 20-50 in my cars.
Gearbos is ST SAE90 is fine but avoid EP oils as the additive attacks bronze bearings. I use SAE120 in the back axle mainly because it doesn't leak as readily but isn't a problem with the ABC as it doesn't have a diff.

i have been running on straight 40 but last year changed to 50
i suppose it depends how worn your engine is ?
and as roger says 90 without additives. wear is minimum but then it depends how many miles you do but generally it will not be many