For short "bursts" 12 volts is OK especially if your just spinning it briefly with no plugs in the motor. Any long duration use of a 6 volt starter, ie cranking and cranking because it won't start using a 12 volt battery will burn it out.
1945 Chevrolet G 506 1.5 Ton Military 4X4 1967 Jeep Cj5 with 283 SBC
