CYLINDER HEAD—E.3
Fig. E.4.
Removing the Valve Collets.
Valve Guides
Detachable valve guides are not fitted, the valve bores
being machined direct into the cylinder head.
When wear takes place in the valve bores restoration
of the original clearance between the valve stem and its
accommodating bore is accomplished by fitting valves
with 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 a
piloted reamer to ensure that the valve position relative
to the valve seat is maintained. Suitable reamers for
carrying out this operation can be obtained from Messrs.
V. L. Churchill and Co. Ltd.
When the above operation has been completed, check
to ensure that the clearance between the valve bore in
the cylinder head and the valve stem is within the limit of
0.0015 in to 0.0035 in (0.038 to 0.089 mm).
Valves and Valve Seats
There will be little wear of the valve stems provided
that lubrication has always been adequate.
Check the valve stems for wear and their fit in the
bores. If the stems are worn fit new valves.
Examine the valve faces for pitting or distortion. Valve
refacing should be carried out on a suitable grinding
machine to an angle of 45°.
When fitting new valves ensure that the valve head
depth relative to the cylinder head face is not less than
that quoted on Page B.7. Maximum depth should not
exceed 0.061 in (1,55 mm) for inlet and 0.055 in (1,4
mm) for exhaust. Check this measurement by placing a
straight edge across the face of the cylinder head and
with feeler gauges measure the distance between the
straight edge and valve head (see Fig. E.5).
The valve seats in the cylinder head should be
reconditioned in the orthodox way, by means of cutters
or specialized grinding equipment, to an angle of 450.
As narrow a valve seat as possible should always he
maintained, therefore, care should be taken to ensure
that a minimum of metal is removed.
Fig. E.5.
Checking Valve Depths.
