Porsche 928 Workshop Manual page 230

a
928 Engine/Cylinder Head, Valves
15
7.Roughen valve guides with Special
Tool 3120.
Proceed as follows:
It is essential to use petroleum as
a lubricant when roughening valve
guides. During this operation,
withdraw reamer frequently to
remove chips. Once bore has been
reamed, finish with dry reamer.
8.The valve-seat rings must be
remachined when the valve guides
have been replaced. It is not
sufficient to grind in the valves
with grinding paste.
Note:
Distinguishing feature, cylinder
head
'85/'86 models '87 models onward
M 28.43/44/45/46 M 28.41/42
Bearing bridge
attachment, M 6 M 8
Exhaust manifold
attachment
2-bolt flange 3-bolt flange
Printed in Germany-XIX,1987
Replacing Valve Guides 15 - 112 i