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Hello All,
Jim Comstock has done a fantastic oil comparison test of about 50 motor oils used in bikes. The tests include temp breakdown , inherent friction, and wear analysis. This work is available on the ACCESS NORTON site. Go to Access Norton online and click on RESOURCES at the top of the main page, and look for Best Norton Commando Oils . I suspect that the needs of a 1975 Commando are similar to the needs of a 1975 Ducati.
Very Sincerely,
Kara

Ooo er.... oil threads are dangerous territory....

Kara, yes when I was researching what oil to use I came across a Norton thread that (I think) contained pretty much the same information as on the page you refer to. Here's a link to your page which is a much better precis of all that information https://www.accessnorton.com/Oil-Tests/NortonOil.php

All I'm going to say is I've used a 10w50 which was the Ducati factory recommendation for a Darmah. And as Craig has pointed out using a multigrade helps the weak starter sprag mechanism on cold starts. I use a Motul 5100 & Nigel Lacey recommends a Silkolene Comp 4 20w50 (for the singles).

Both are SG rated but most important is to change it often.

Andy B