complete scratch built frames?
tricky stuff but not if you do them regularly.
measurements seem to be the factor here...where to start?
what engine? iunno what country youre in but everyone should have hondas! z50, sl50, c50...or 70's. copy those engine mounts, as theyre china motor standard sizes, and surely, anywhere, china parts are cheaper?. not sure about the larger honda 90/110's such as the "nice", as found in other countries. not in au... all i know is the CT (aussie=postie) 90 and 110's are not the same engine mount pattern!
ground clearance? wheelbase? what forks? you can fabricate up a set of springer/linkage forks if you have someway of making decent pivots...brass bushed preferably.
suspension travel. dependant on shock.
swingarm length? a component of both wheelbase and ground clearance, and the shocky mount position is determined by possible wheel travel, as well as the shock.
the ratio of length for the swingarm pivot to shock and swingarm pivot to axle is the leverage applied to the shock, which is where spring pressure/rate is important.
heavier springs allow for longer swingarms/ more leverage, but require more engineering to take the extra pressure... you can also get more travel from a given length shockie.
angle of shock during travel affects "rising rate"... the correct angle and its progressive, the wrong angle and all the flaws of the shockie itself (internal design) become more apparent, or the thing just wont work. the two extremes.
headset/ steering angle/ fork rake/wheelbase/trail....
commercially, most headstem tubes are welded then machined to take the bearing cups/seats. a really hard thing to do at home... got a mill? and adjustable boring head? otherwise accuracy is reduced...could be safety issues.
the angle of the tube affects turning speed and stability. it affects wheelbase when combined with fork length. theres rake; offset of axle parallel to head tube, and trail; how far the axle is behind the tyres contact patch in a vertical line. both affect stability and steering.
and everything has to be centralised in the direction of travel... chain offset... brakes...exhausts...pedals/controls... best to leave it to the pros... start saving... if you can get a cr250... bikes must be available...
i got some old yamaha600 thing here thats just wanting a 140 or summink stuffed into it....
nah. this is really the wrong forum to be looking up info on scratch built frames...
just bought ones
the list of measurements is pretty extensive. and possibly beyond the scope of anyone not familiar with marking out tables and real measuring equipment like calipers.
the other option is to measure pictures and scale them
then its jig time