How tight should the bolt be to keep the cranks on without knacking the bearings (laterally)

Trying to find the right balance – too tight and you can feel the bearings. Too loose and the drive side crank starts to loosen

The bolt should be as tight as possible, RF cranks require a BB shell to be an exact width to work with this, so either your BB shell is oversize and needs facing back(I usually go to the 0.25mm undersize min recommendation), or you have too many spacers, either on the axle or behind the cups.

Buy a King BB.
That way you get some shims that you can alter the tension on the bearings with.
Currently using a King BB with a RF fatbike crank and the shims allow enough tuning to get it running just right.

The RF cranks should have a set of axle shims fitted to the axle already. Remove enough of these to let you tighten the crank bolt fully home without leaving any lateral play.

The shims that come with the RF cranks aren’t small enough to make the correct adjustments.
Also I think the fatbike crank comes with more adjustment than the 68/73 crank.

Cheers

King BB would be nice – ill have a play with washers and see if it makes any difference. Should be easy to get it faced and fitted properly at LBS

And then see if I want need a king.

You could just try and get some King shims?

WTD ad going up now

Cheers!