Flywheel / ring gear holding tool
Moto Guzzi V700, V7 Special, Ambassador, 850 GT, 850 GT California, Eldorado, and 850 California Police models
See Moto Guzzi Workshop Manual, MG# 12911801
Duplicate of the original factory tool
MG Cycle sells a duplicate of the original factory tool. Very nice.
Ray Hale originally suggested using a flywheel lock / flywheel holder for a Volkswagen Beetle. Not as good as the original tool (as it only holds the flywheel in place when the ring gear is fitted), but it works well and is far cheaper. Toss the bolt and nut it comes with. Just slip the hole over one of the protruding studs in the bell housing and the teeth will engage with the ring gear.
These are commonly available from many locations, including:
DIY ring gear holder
Thanks to Joe Tokarz for sending me this information via e-mail. In Joe's own words:
Here is an alternative to a store bought ring gear holder. It's made from a scrap piece of 1⁄8 inch aluminum.
Place the metal piece behind the ring gear and with a sharp pencil or awl; scribe the locations of the ring gear teeth. Then file out the teeth. Not very scientific but it works.
Through filing and fitting, shape the fit of the teeth and add a curvature across the tops of the teeth so they engage the gear teeth fully.
Use a paper template to locate an accurate location of the stud hole. Place the template in the gear teeth and mark the hole, then transfer that to the holder.
Slip a simple spacer over the stud so the holder can engage the gear teeth.
An oversize nut takes up the space where there are no stud threads. Snug the holder to the stud now the ring gear is steady.