A cutting tool has a main body and a cutter. The main body has an outer peripheral surface having one end and the other end. The cutter is fixed to the main body. The main body is provided with a hole extending in a direction from a region surrounded by one end toward a region surrounded by the other end. When viewed from this direction, the shape of the opening of the hole is circular, and the hole is provided inner than the outer peripheral surface. The cutter has a member disposed inside the hole.

Two cylinder heads are disposed side by side. Upper side intake valve holes of one of the cylinder heads and upper side exhaust valve holes of the other of the cylinder heads are simultaneously machined by a multi-spindle head integrally including intake side tools and exhaust side tools. After moving the one of the cylinder heads upward by a pitch of the intake valves and moving the other of the cylinder heads upward by a pitch of the exhaust valves, remaining intake valve holes of the one of the cylinder heads and remaining exhaust valve holes of the other of the cylinder heads are simultaneously machined.

Two cylinder heads are disposed side by side. Upper side intake valve holes of one of the cylinder heads and upper side exhaust valve holes of the other of the cylinder heads are simultaneously machined by a multi-spindle head integrally including intake side tools and exhaust side tools. After moving the one of the cylinder heads upward by a pitch of the intake valves and moving the other of the cylinder heads upward by a pitch of the exhaust valves, remaining intake valve holes of the one of the cylinder heads and remaining exhaust valve holes of the other of the cylinder heads are simultaneously machined.

Cutting insert with a cuboid body has a substantially square top face and bottom face, said top face and bottom face connected by four peripheral adjoining side surfaces. At least two cutting edges are formed at the transition of the top face to at least two side surfaces, that cutting edges defining a plane of the top face. To provide a cutting insert and a corresponding tool suited to produce valve seat surfaces with high precision but still having a rather simple construction and being precisely mountable with ease and less efforts of adjustment, the plane defined by the top face cutting edges of the cutting insert has maximum dimensions of 7 mm7 mm, where the bottom face has a supporting surface formed exactly parallel to the plane defined by the top face cutting edges by means of grinding within a tolerance of less than 5 angular minutes.

Cutting insert with a cuboid body has a substantially square top face and bottom face, said top face and bottom face connected by four peripheral adjoining side surfaces. At least two cutting edges are formed at the transition of the top face to at least two side surfaces, that cutting edges defining a plane of the top face. To provide a cutting insert and a corresponding tool suited to produce valve seat surfaces with high precision but still having a rather simple construction and being precisely mountable with ease and less efforts of adjustment, the plane defined by the top face cutting edges of the cutting insert has maximum dimensions of 7 mm7 mm, where the bottom face has a supporting surface formed exactly parallel to the plane defined by the top face cutting edges by means of grinding within a tolerance of less than 5 angular minutes.

An apparatus for centering a pilot tool within a valve guide during valve seat cutting is disclosed. The apparatus includes a pilot tool and an adapter. The pilot tool includes a shank, and an extended section extending from the shank. The extended section includes an upper section and a lower section. The upper section extends from the shank, and the lower section extends from the upper section. The upper section includes a tapered section, and the lower section includes a straight section. The adapter receives the shank. In one embodiment, the upper section engages with the valve guide to operate the pilot tool as a fixed pilot to center within the valve guide. In another embodiment, the lower section operatively contacts the valve guide. The adapter rotates causing the lower section to rotate within the valve guide, and operate the pilot tool as a live pilot for centering within the valve guide.

An apparatus for centering a pilot tool within a valve guide during valve seat cutting is disclosed. The apparatus includes a pilot tool and an adapter. The pilot tool includes a shank, and an extended section extending from the shank. The extended section includes an upper section and a lower section. The upper section extends from the shank, and the lower section extends from the upper section. The upper section includes a tapered section, and the lower section includes a straight section. The adapter receives the shank. In one embodiment, the upper section engages with the valve guide to operate the pilot tool as a fixed pilot to center within the valve guide. In another embodiment, the lower section operatively contacts the valve guide. The adapter rotates causing the lower section to rotate within the valve guide, and operate the pilot tool as a live pilot for centering within the valve guide.