TC reported MCH stuck at B3 and unable to depart in ATPM (PSD work at MRB SB RIMS #380522). AM mode disallowed was removed for TC to proceed in AM mode -ok. Sto ck change over arranged at JUR. TC reported MCH stuck at B3 ~~~~~ 3640-TC reported MCH stuck at B3 and unable to depart in ATPM (PSD work at MRB SB RIMS #380522). AM mode disallowed was removed for TC to proceed in AM mode -ok. Stock change over arranged at JUR.(L3) L3 3640 ER D/L, MCH in ATPM fault was unable to duplicate. Found #3640 MCH switch gear mountingwas over tightened slightly Postulate this caused gear teeth to dip lower on switch side compared to bearing side. This may have caused the MCH to be intermittently stuck during movement of MCH. Loosened & tightened all bolts. Security/Function test MCH & MS - OK, no abnormalities found.  Lee JC 44956