An adjustable removable grinding arrangement for grinding inside annular openings in bottom portions of water hydrants. The grinding arrangement comprises a router having an energizable motor with a grinding tool attached to an end thereof, a base plate supportively attached to an end of a housing of the router, a support plate pivotally attached to the base plate attached to the router, and an annular guide ring having securement studs for removable securement to a rim of an opening on a lower end of a hydrant. The support plate is rotatable on a plurality of wheel members engaged with the guide ring to permit the grinding tool of the router to remove material from the rim of the hydrant as the support plate is rotated about the guide ring.