Portable grinding machine for resurfacing cylinder head retainers

A portable grinding apparatus for the in situ refinishing of an out of square engine crankcase retainer seat and insertable in a cylinder thereof, having at least two substantially rigid positioning discs, said positioning discs being axially attached in spaced vertical arrangement to a central shaft, each of said positioning discs having a diameter closely approximating and slightly smaller than the interior diameter of said cylinder, the lower of said discs serving to initially orient and center said apparatus within said cylinder and an upper disc having expansion slits which cause the periphery of said disc to expand when said disc is forced upon a tapered portion of said central shaft, said expanded disc periphery thereby orienting and immovably securing said apparatus within said cylinder parallel to the axis of the cylinder bore, said positioning discs rigidly securing said apparatus about the periphery of said cylinder at at least one position and locating said apparatus at a fixed attitude perpendicular to the plane of the retaining seat at at least two positions about the periphery of said cylinder, a powered grinder tool rotatably attached and adjustable for vertical travel on said central shaft, for the rotation of the grinder tool about the central shaft, thereby grinding the seat to a desired depth and resulting in a finished surface on the seat substantially perpendicular to the axis of the cylinder bore.