Porsche 928 Workshop Manual page 197

929
Englne, Cylinder Head, Valve Drive
15
Machining the cylinder head mating surface
Checking the cylinder head for distortion
Check the sealing surface of the cylinder
head for distortion using a feeler gauge
and straightedge.
Distortion limit of mating surface:
0.05 mm. Warped cylinder heads may
be repaired by machining the mating
surface. Admissible distortion after
machining: 0.03 mm
Machlnlng the cylinder heads
As a rule, both cylinder heads must be ma-
chined by the same amount to ensure
correct seating of the regulator housing.
Machine sealing surface of the cylinder head
only until a straight surface is obtained.
Max. wear limit: 23.6 mm.
Note for machining of the sealing surface:
Max. roughness = 0.015 mm
If machining causes the actual value to be
below the tolerance applicable to new pans,
use a 1.4 mm thick cylinder head gasket
(available from the parts service) when fitting
the cylinder head.
New-part size A = 24 * 0.1 mm
Wear limit A = 23.6 mm
Note
When machining the sealing surface facing
the combustion chamber, also check the mat-
ing surface on the camshaft end and machine
if required.
Admissible distortion of camshaft mating
surface
whenchecking: 0.1 mm
after machining: 0.03 mm
Before machining the mating surface facing
the camshaft housing, check dimension "A' to
avoid unnecessary work.
Plug oil passage of check valve before ma-
chining. Remove roll pins.
Cyllnder head refacing dimenslons and
Identification
New dimension
:24+0.1 mm
Gasket
: 1.1 mm
Identification : none
Refacing dimension
: 23.8 to 23.6 mm
Gasket
: 1.4 mm
Identification
:N
Identification: N
Engrave at cylinder 1 and 4 as well as 5 and
8, respectively.
Height of "N" character: 10 mm
Machlnlng the cylinder head matlng surface
Printed In Germany -XXIX, 1332
15 - 19