imho the main cause of head shake is a cupped front tire. Tires can cup real fast like when underinflated. Metzelers 880s and 888s: 41psi front, 42psi rear.
Next would be loose headset,
then alignment.
Worn headsets usually means the races are notched and the steering will find said notch when you un-weight the front wheel when jacking up the bike.
