Abstract: The invention pertains to a boring tool for boring cylinder chambers of internal combustion engines without removing the engines from the vehicle chassis. A housing affixed to the engine block includes a rotatable driveshaft supporting a cutting tool whereby rotation of the driveshaft by an electric motor causes linear movement of the driveshaft to feed the tool. Tool advance is produced by a spiral groove pump defined upon a piston mounted on the driveshaft located within an oil-filled cylinder defined in the housing. A valved fluid passage located in the driveshaft piston selectively permits the pump to be bypassed for axial rapid traverse movement of the driveshaft and tool.