Before servicing or repairing a valve, first remove all carbon residue from the combustion chambers, valve ports, valve stems, valve stem guides and head. By using a machine, turn the intake and exhaust valves to the needed position and always leave at least 0.787 mm (0.031 inch); if there is less, use a new valve. When refacing a valve seat, install the proper pilot in the valve guide bore and only file away a little metal using a dressing stone to make a smooth finish on the valve seat. Use tapered stones to get the right seat width and keep valve seat runout less than 0.0635 mm (0.0026 inch.) Choose your preferred way to measure, remove the valve from the head, wash the guide bore with solvent and a brush, fit a telescoping gauge 9.825 mm (0.375 inch) inside the guide bore near the valve spring side and measure with a micrometer. Measure across and then down the contact on the engine cylinder head and if the gap between the two measurements is more than 0.0635 mm (0.0025 inch), use an oversize valve stem and ream the guide bore. If the bore diameter measured in your valve doesn't match the correct range between 0.313 and 0.314 inch (7.95-7.97 mm) by over 0.076 mm (0.003 inch), you should ream the bore for an oversized valve stem. Another way to check is with a dial indicator, placed before the valve reaches its seat and the valve guide open a little, so you can see how far the valve stem moves. If the reading is more than the 0.025 - 0.0762 mm (0.001 - 0.003 inch) range, ream the guide to match an oversize stem. After reaming the valve guides, the seats should be ground to match the valve guide.