Re Nick:

I can see that you have compiled a much more accurate equation - which I would no doubt advise those fabricating more costly and complicated systems to use - but my guide so far was much created to provide an easily understandable rough calculation means for the practicle application of four-bar lifters in most given instances. Of course, as you have found, it may not be suitable for some cases.

My second much more complicated equation should give a solution to the problem that you have encountered with my equation. I hope that I can construct an online calculator which will allow people to enter the figures required without any knowledge of the equations behind them to solve their 4-bar requirements. I dont think I shall get round to this until Summer or thereabouts though as Im piled under far too much work at the moment and for much of the forseeable future.

Ewan