Abstract: A mechanism secures a mud agitator motor on top of a man-way cover on a mud tank. The mechanism includes a retractable shaft retainer element arranged to engage a retainer block affixed to the agitator shaft. A pair of hemi-cylindrical coupling halves couple the agitator motor shaft to the agitator shaft. The retractable shaft retainer element, once engaged with the retainer block, secures the agitator shaft. The coupling halves can then be quickly and easily removed, and the motor can then be removed for repair or replacement.