Thank you, Weld, that makes perfect sense! Thank you, Pliskin, for getting back to us!
I m just concerned with overtorquing. Is it possible to overtorque a large nut by hand? Or is that the result of an air impact gun?
The Zong GY-2 manual has an entry under "Nut of rear rocker arm", giving two sizes (M12 and M14) with 30 and 70 nm max respectively. I m not sure they mean the swingarm, what do you think? M12 could be the bolt and M14 the nut, though.
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1971 Garelli Gulp 50cc with open ports and 16 mm Bing Carbie + 1980 Honda XL
223 ZS 
+ 2007 Zongshen LZX200G + DR400SM