which engine oil?

[jimbo]

Any synthetic/semi-synthetic was judged a waste of money in an air-cooled engine

Complete and utter rubbish. with the possible exception of the piston/bore interface, I can't see why bearings are likely to behave differently dependant on the engine cooling method.
If anything I would think air cooled would more require synthetic for the bores, as this oil behaves more consistently over a greater operating temperture.

 

[cookie]

mineral will fry quicker than synth in an air cooled engine if you are stuck in traffic etc. as there is no efficient cooling system while stationary.

 

[Fitzdangle]

FLT oil

To be honest i'm not realy up on these technical specs

I use the oil that we put in our fork lift trucks at work its 10/40 made by Esso and its FREE !