Engine - Machining Valve Seats, Checking Valve Guides
87porsche04Subject: Machining Valve Seats and Checking
Valve Guides on 4 Valve Cyl. Heads
Model
928S, 928 S4, 944S
Group
1
Part Identifier
1560
Number
8722
December 31, 1987
Hydraulic lifters will not operate properly if the valve stem protrudes too high.
After machining valve seats, distance A and B (valve stem end to cylinder head contact surface for the valve spring retainer) should not exceed the following values:
928S Model Year 1985 and 1986 Intake valve max. 43.0 mm (A) Exhaust valve max. 42.1 mm (B)
928 S4 and 944S from Model Year 1987 Intake valve max. 44.4 mm (A) Exhuast valve max. 43.4 mm (B)
Measurement should be taken with valve spring, spring retainer, and shim removed.
If distance exceeds the specified value, measure it again using a new valve. If distance still exceeds the specified value, replace the valve seat or cylinder head.
Checking Valve Guide for Wear
Wear limit 0.8 mm for 2 valve and 4 valve engines measured with a new valve.