Hi Malcolm ,
The equivalent eccentric concept is not always the most helpful way of designing simple valve gears .
It's an enormous subject but I'll make a few suggestions :
(1) Just use the old fashioned layout on a drawing board method – move things around on paper until it all works out . CAD helps because of the accuracy and rapidity of making changes .
(2) Use the equivalent eccentric idea with a postulated set of starting conditions – eg guess a plausible valve travel and / or an initial setting of eccentrics . Adjust set up progressively until again it all works out .
(3) Set up a computer model either using one of the available programs or just using BASIC or spreadsheet ..Either use multiple iterations to optimise or drive the design yourself using progressive changes .
(4) There is a math method but we'll leave that one for now .
Get back to me if you want any more specific help .
Regards ,
Michael Williams .
nb: It is actually a common problem in engineering to be faced with large set of variables and only a few things positively known . Inspired / intuitive guesswork , experience and simple calcs are often used to have a first stab at a design which is then progressivley refined .
nb : Solutions to design problems are not usually unique . A quite simple problem can have multiple valid solutions – and this is true of valve gears .