Machining Valve Seats; 15-8A; Checking Valve Guides - Porsche 928 Workshop Manual

a
926 Englne I Cylinder Head, Valves
15
Machining valve seats
Note
Before refacing the valve seats, check dimen-
sion "A" to avoid carrying out work that may
be unnecessary if the wear limit has been
exceeded.
Remove no more than the absolute minimum
amount of metal in order to prevent prema-
ture wear.
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Checking valve guides
1. Remove deposits with a cleaning reamer.
2. Place new valve in valve guide and check
that valve stem end is flush with cylinder
head/camshaft housing mating face.
Valve seats may be machined down to the
wear limit "A" = 14.5 mm
(size new 13.65 f 0.45).
Check with a new valve.
Distance "A" must not be exceeded, as other-
wise the function of the hydraulic valve tappet
would not be assured.
3. Check clearance with dial gage holder
VW 387 and dial gage.
Wear limit = 0.80 mm.
a
Machining valve seats, checking valve guides
Printed in Germany - XXVII, 1991
15-8a