i am building a full case 1/2 vw. has any one used a scooter or motorcycle stator on these engines. I would like to bolt the rotor to the end on the crank and the stator to a bracket all inside the case.
The rotor has the centre rivetted on. That makes it quite amenable to modifaction to alternate engines. The GY6 crank is fairly small in diameter, so trying to fit it GY6 style onto a big crank is not going to work, the stator will clash. Hanging off the end, should be good if you can reliably locate the stator. Another possible issue is that the VW revs a lot lower, you may not get good charging voltage. Rewinding the stator for lower RPM is doable, though. I rewound one as I had an AC system and could not find the correct relacement stator with correct CDi and charging coils. I probably still have some GY6 bits lying around, would you like to me to see if I can find them and physically measure them? I think that the 50cc and 150cc differ only in crank adaptor size.
It may also be possible to use the GY6 ignition system, doubling up after the pickup. With the low RPM, the DC version may be preferable. I have no idea what the advance curve is like or whether it will suit a VW. But, the parts are cheap and light...
Lifepo4 can be charged directly. But should still have a charge controller or ballancer. Plenty of lifepo4 batteries for powersports. They weigh about as much as 2 smart phones. Powerful enough to crank my 4.0l v6 toyota tacoma. I have them in my jet skis and they do fine on a stator with a voltage regulator.