Porsche 928 Workshop Manual page 284

17 Engine - Lubrication
928
CLEANING OIL CHECK VALVE FOR HYDRAULIC VALVE TAPPETS
Note:
The oil check valve prevents the
oil from flowing back out of the
cylinder head, thus assuring
operation of the hydraulic valve
tappets. If the valve tappets
chatter as the engine turns over
just after starting, it is
essential to clean the check valve.
1 - Threaded rod
2 - Spring guide
3 - O-ring
4 - Compression spring
5 - Ball
l.Remove cylinder-head cover. Screw
a hex bolt, e.g. M 6 x 40 down
into spring guide. Slacken
threaded rod 2 turns and lift out
valve guide.
2.Use a magnet to withdraw
compression spring and ball.
Thoroughly clean ball seat, ball,
compression spring and oil duct.
The ball seat remains in the
cylinder head and great care must
be taken to ensure that it is not
damaged.
3.Replace O-ring before
installation. Tightening torque
for threaded rod 3.5 Nm
(2.8 ftlb).
17 - 10 Cleaning Oil Check Valve for
XIX,1987
- Printed in Germany
Hydraulic Valve Tappets