CYLINDER HEAD—E.3Fig. E.4.Removing the Valve Collets.Valve GuidesDetachable valve guides are not fitted, the valve boresbeing machined direct into the cylinder head.When wear takes place in the valve bores restorationof the original clearance between the valve stem and itsaccommodating bore is accomplished by fitting valveswith oversize stems. Three service valves are available,for both inlet and exhaust, with oversize stems of 0.003,0.015 and 0.030 in. (0.08, 0.38 and 0.76 mm)respectively.In order to fit the 0.015 and 0.030 in oversize valves,the bores in the cylinder head must be reamed with apiloted reamer to ensure that the valve position relativeto the valve seat is maintained. Suitable reamers forcarrying out this operation can be obtained from Messrs.V. L. Churchill and Co. Ltd.When the above operation has been completed, checkto ensure that the clearance between the valve bore inthe cylinder head and the valve stem is within the limit of0.0015 in to 0.0035 in (0.038 to 0.089 mm).Valves and Valve SeatsThere will be little wear of the valve stems providedthat lubrication has always been adequate.Check the valve stems for wear and their fit in thebores. If the stems are worn fit new valves.Examine the valve faces for pitting or distortion. Valverefacing should be carried out on a suitable grindingmachine to an angle of 45°.When fitting new valves ensure that the valve headdepth relative to the cylinder head face is not less thanthat quoted on Page B.7. Maximum depth should notexceed 0.061 in (1,55 mm) for inlet and 0.055 in (1,4mm) for exhaust. Check this measurement by placing astraight edge across the face of the cylinder head andwith feeler gauges measure the distance between thestraight edge and valve head (see Fig. E.5).The valve seats in the cylinder head should bereconditioned in the orthodox way, by means of cuttersor specialized grinding equipment, to an angle of 450.As narrow a valve seat as possible should always hemaintained, therefore, care should be taken to ensurethat a minimum of metal is removed.Fig. E.5.Checking Valve Depths.
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