Mercruiser Alpha Impeller Kit | Sierra 18-3217 Mercruiser Alpha Impeller Kit | Sierra 18-3217 Includes impeller, gaskets, o-rings, grommet, wear plate, & water tube for Mercruiser #1, R, MR, & Alpha I stern drives. Sierra Mercruiser impeller repair kit For Mercruiser #1, R, MR, and Alpha I stern drives thru s/n 0D494568 Does not include housing or base Replaces Mercruiser 47-89984Q5, 47-89984T5 Replaces Mallory 9-48304