Starter Solenoid Shimming for Gears?

[duwem]

I have read you need to adjust the solenoid postion on these old starters so the starter gear travels to the right positions in relation to the ring gear.

Can someone elaborate on this? My solenoid is the type that bolts to the top of the starter with 4 bolts, sloted holes in the bracket. Some use 2 bolts to the starter head and use shims instead of slots.

Something about manually activating the plunger and a paperclip?

Thanks