1952 Es2 primary chain

The clutch will always have 42 teeth...Chain length will depend upon engine sprocket size. 

Sounds correct then. The WD16H with 18t engine sprocket had 74 and I have a half-link running 19t.

The ES2 went to swing arm in 1953 so yours should have plungers. The chain gets tighter at full bounce and rebound so whatever the book says will only be a guide. You might have to add or take away links or even a half link to make sure it doesn't end up bar tight.

Also of course the chain is 5/8 × 1/4".  When asked why they used a narrower chain than most, Franks allegedly simply replied "why not?" And he was a better motorcycle engineer than most of us.

... is of course true but the question was about the primary. What is worth checking is that the primary hasn't been overadjusted ie the gearbox moved right back. And of course when adjusting the pprimary always finsih up by adjusting the box forward to take up any play.

... coming loose bacuase the B4/662 dowels have fretted the holes they register in so allowing slight movement which loosens the studs. You get a similar effect on the QD wheel if the sleeve nuts have ever been allowed to loosen - the taperes wear and you can never tighten them up properly.

Loctite may work but I would put it on the dowels as well although this may make future dismantling harder.

... the load reverses on the overrun but admittedly is less than when being driven.