
THE RECIPROCATING PISTON PETROL ENGINE 49
Conventiona
high fnctior,
lock
Low' friction (Action of spring)
release type Valve opening valve closed
Figure 1.91 Methods of valve spring retention
washer with a central conical recess. Seating in the
latter is a pair of split-type wedge collets which in turn
engage a shallow groove machined near the top of the
valve stem (Figure
1.91a).
The pressure exerted by the
valve spring therefore holds the collets tightly in place,
yet they can readily be removed (albeit with a little
persuasion from a soft-faced mallet in some cases!) by
depressing the spring while holding the valve closed.
This method o