i have made crankcases in the past, simple british bike cases manualy and modern ones using a cad program and a home made milling machine.

not realy worth the effort (or expense if somone else is making them) in my opinion unless you realy cant get ready made cases or making specialist racing parts.
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Honda nc23 CBR400 AERO 1986, 1990 honda NC23 Tri-Arm, 1987VFR400 NC24 Rothmans Rep, NSR250 MC16 1987, CL250s 1983. Moto guzzi zigolo 110cc 1958. Fantic 50cc 1972. Suzuki Cobra Race bike 500cc 2t 1975 , GP125 1975. Triumph T110 1954. BSA Thunderbird 1955. Ariel VB 600 1952, 1990 MuZ 125 etz.