What oil are you using in your primary chaincase?

[Adrian1]

Is castrol 4T too thick? Obviously has to be free of friction modifiers.

 

[harper6t]

I am talking Pre-unit here, I use a Penrite 20-50, I think the friction modifier fear is probably a bit misplaced these days, they don't seem to have the same sorts of modifiers now as they used to have.
Also not sure that a thick oil would be that bad in the chaincases, there shouldn't be that much in there. I also have a Velocette that vents a lot of oil out the main bearing into the chaincases, so much so that I drain the oil from the chaincases before each ride, it is run on Penrite 40-70 and I haven't had any problems with the clutch slipping.

 

[Adrian1]

Thanks for your reply. You've reminded me that some
bikes circulate their engine oil through their chaincase, then back into the motor. Enfield for example. I intend to use the Castrol 4T I have on hand.

 

[grandpaul]

I like 4T and Valvoline equivalent.

 

[Rocky]

I use Castrol 30 in the primary of my '67 BSA single.
My Triumph Tiger 100 is unit construction and shares the engine 20-50w oil with the primary.