When the rear wheel hits a bump it's movement will not be exactly up/down but will describe a slight arc because it is rotating about the swingarm pivot. On a twin shock bike this rotation will very slightly alter the angle they are at wrt to the frame/swingarm so they, in turn, will also need to rotate slightly around their mounting bolts. One thing I've never been sure of is, is this designed to happen by the metal sleeve in the bush rotating around the bolt (even when the metal insert is bolted tight against it's frame/swingarm lug ) or should the movement be taken up by the rubber portion of the bush(es)?
Its taken up by the rubber twisting slightly. More for cars, but when changing suspension with rubber bushes the bolts should be tightened with the weight on the suspension so the bushes aren't always twisted. Most new bikes will probably have solid bushes or bearings now I guess.
Triumph lugs were compressed by the bolts against the ends of the bushes. If you took one end of the pivot bolts (as Meriden called them) off, ie subframe, or swing arm, the shocks would stay (more or less) in position. So, you'd lubricate the bolts to stop the bushes seizing on them, rather than to provide a bearing surface.
On the Darmah both ends of the shock are bolted to the outside of the frame/swingarm mounting lugs rather than been 'pinched' in the middle of one. I'm not sure how this affects it's strength. I was musing over this particular conundrum whilst removing the shocks in readiness for a new chain & swingarm saver when I came across a rather worrying issue - the top bolt on the rhs shock is bent My first thought was perhaps it had bottomed out real hard on a deep pothole and the above described manner of mounting isn't that strong. However further investigation showed the distance between the top & bottom mounts are different on either side of the swingarm - by about 2mm. I've always had trouble with these shock bolts requiring a lot of faffing about to tighten them all up but have never seemed to be this much out. So I'm now wondering if somehow the swingarm is not sitting square.... or is this just the standard Verlicchi maufacturing 'tolerances'
I was thinking about my old AJS, on which the shocks mounted over studs fixed on the frame/swing arm. Surprisingly slim, with nuts to suit, 1/2" spanner probably. They never bent though.
