Frister & Rossman cub 7 Back thread guide keeps coming loose?

If you are referring to the small circular chrome wheel mounted on the top rear of the m/c, the answer is yes there is a very light spring about 8mm in diameter and about 6mm long when uncompressed. It is assembled after removing it from the m/c as follows.
1. Backplate 2. Flat plate with arm coming off next (bend at end of small arm locates in groove at top rear of M/c)
3. Small wheel, concave side out. 4. lay spring inside this wheel. 5. Large wheel, Convex side out (thus trapping spring). 6. screwed together tightly from rear with small countersink screw. Then refit to top casting of M/c. Refit top casting to M/c (2 Screws on top)

BP
March 2013