I have done a quick voltage measurement with a small 12 pole motor i have, base on similar principle, with permanent magnet in outer rotor.
By turning the shaft by hand quickly, then taking the photo, at about 100RPM it generates over 8 volts ac.
The big washing machine motor should work very well, The problem here is to get a proper bearing to center the rotor. The washing machine bearing was impossible to remove from the machine (corrosion on the drum) and was left on site.
I use this in my workshop to quicky advance low voltage steppermotors in kWh counters to check if they advance correctly.http://farm1.static.flickr.com/181/457283590_eff2827b23.jpg
Tacho gen. Openhttp://farm1.static.flickr.com/202/457283588_619a490103.jpg
Tacho gen. 8.24 volts ac