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Cylinder Head Valve Seat Grinding Tools

The cylinder heads in the four-stroke combustion engine have valves and valve seats that must be machined to precise tolerance and fit. If the valves do not seat correctly with their seats, they leak and lose compression. Valves that do not match within specifications with their seats can also cause excessive overheating and valve failure. The valve seat takes a continual pounding from the action of the valve when it closes. Valve seats can crack and become worn. Several tools need to be used to check and repair valve seats.

Crack Checking Tools

Before any valve seat can be reshaped and ground within specifications, the vale seat area must be magnafluxed to reveal hairline cracks. An electrical transformer attaches to the head, where it delivers a a high voltage magnetic charge to the metal. Magnaflux, which consists of a powdered, reactive chemical, gets sprinkled on the valve seat area. The chemical power reacts to breaks in the magnetic lines of force (field), which shows up as horizontal lines or spider-webbing cracks in the metal.

Valve Seat Grinding Machine

The valve seat grinding machine consists of of a platform vice that holds the cylinder head in a fixed and upright position. The vice fasteners lock the head into a level and stable orientation. The overhead part of the valve seat grinder consists of a motor that drives a cutting bit, which can be adapted to cut out the old valve seat from either aluminum or cast iron. A machine bit then cuts the new valve seat face at a precise angle, usually around 45 degrees. Dial indicators determine the depth of the cut, while bits determine the seat diameter to be cut. Lubricant, fed by the machine, keeps the cutting surface cool.

Valve Lappers

Valve lapping tools must be used to attain final sizing of the face and valve seats for a perfect, sealed match. The most common valve lappers consists of wood dowels that have two different size suction cups on each end. After the valve has been inserted in the stem and abrasive compound has been brushed between the valve face and the seat, a manual twisting motion turns the wood dowel back and forth to cut the interface seat between the valve and seat. Valve lappers come in a variety of suction cup diameters for intake and exhaust valves of all sizes.

Motorized Valve Lappers

Instead of manual wood dowel lappers, motorized drills and air guns can be fitted with suction cup bits that attach to the top of the valve. Once abrasive lapping compound has been applied between the valve and seat, the motor or air tool is turned on to spin the valve at high rpm. The use of power tools for lapping reduces the labor time involved in cutting the final seat and valve face.

Valve Seat Grinding Compound

Valve seat grinding compound consists of a a thick paste that contains cutting abrasives. The cutting compound comes in fine, medium and coarse grits. The coarse grit takes the most of the irregularities and burs out of the interface surfaces, while the medium and fine cutting compound cuts the last finishing face between the valve and valve seat.