David H. Neumann wrote on 10/04/2007 :
Harry: An M8 x 1.25 mild steel threaded rod (property class 4.6)
subjected to only axial tension, with no applied bending moment nor
applied shear load, can withstand a static, allowable, applied
tensile load of 4400 N, with no onset of yielding in the threads, if
the nut isn't torqued beyond 5.5 N*m. This means it can support a
gently-applied (not bounced nor suddenly dropped) allowable mass of
448.7 kg in tension.

It would be in tension supporting and lifting the bikes weight of 200Kg
plus around 30Kg or so for the frame part which moves. A welded on to
the rod nut at the top, passing through a bracket at the top of the
main lifting post, then a captive second nut pulling on the actual
lifting frame with the bike sat on it. Turn the top nut and the rod
screws into the lower nut pulling up the frame. The only loading apart
from the weight is that of turning the rod to achieve the lift.

It sounds as if 12mm would be a more suitable size to give an extra
margin.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk