what engine oil and gearbox do i put in atlas 64

Semi synthetic 20/50

     A recent forum thread had a similar topic, well within a year, also dealing with "high zink" classic blend, agricultural machine. Some modern car oil ,usualy much thiner than 20/50,will melt/corrode brass,copper,bronze .
  Also, chaincase oil should not be "friction modified",in deference to th clutch. Some ATF also is. 
  So much more in th other thread. l don't know how to use the search feature.

In my 60 + years of "Nortonning" I have used all manner of oils in my Heavy Twins , I am a natural experimenter ( my mum called me the proffessor when  a 5 year old young child!) . I have used 30 HD diesel ,lawn mower oil, 30,40,50 monogrades, with and without detergents ,VW /Porsch  aircool  spec oils , Multigrades 10/40 and 20/50 and fully synthetic 10/40 Yamaha oil .  No bearings wore out,no piston rings failed ,no cam problems, nada .  So yes , use oil , always!.  What have i found of interest ? , Thin oils get used up .and the engine sounds a bit more rattley , Thick oils make for heavier kickstarting . Detergent oils clean your engine . Fully synth oil has unbelievably  much better protection against siezure if you cock up with the carb settings and it gets so hot it will keep going with the ignition turned off !. Dont use synthetics in your clutch , change oil regularly,fit magnets and an air filter  and keep a record.of oil changes  ,your piston rings and bore will thank you . 

The only real unsuitable oil experience I've had is use of Castrol GP50 (SAE50 grade) in the engine of a Triton, in cool Scottish autumn weather.

It appeared to be too thick, on a cold morning, to flow from tank to pump: the pressure indicator showed a loss of pressure as revs passed about 3500.

I now use fully synthetic 20W/50 engine oil in the same Triumph 650 engine. I think it prevents most engine wear, but I can't prove it and I'm happy for everyone else to do differently!

I have been using 20W/50 Fully Synthetic Oil for the last 6,000 miles in my 650 Dominator. The engine does now sound a bit like a Triumph Twin when running but the two plus points are......
No more smoke screens on cold start-ups plus oil consumption is well down on long fast rides. 
I am now adding just a mug full every 1,000 miles. Previously it was a pint every 500 miles.

Fully synthetic 20/50 is not easy to find at a reasonable price . Its my next experiment .  A 30/60 oil would suit me perfectly .