Volkswagen Corrado (1993 year). Manual - part 134

ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION 

         CYLINDER HEAD OVERHAUL

         * PLEASE READ THIS FIRST *

NOTE:    Always refer to appropriate engine overhaul article in the
         ENGINES section for complete overhaul procedures and
         specifications for the vehicle being repaired.

         DISASSEMBLY

         Mark valves for location. Using valve spring compressor,
compress valve springs. Remove valve locks. Carefully release spring
compressor. Remove retainer or rotator, valve spring, spring seat and
valve. See Fig. 2.

Fig. 2:  Exploded View of Intake & Exhaust Valve Assemblies - Typical
This Graphic For General Information Only

ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION 

         Clean cylinder head and valve components using approved
cleaning methods. Inspect cylinder head for cracks, damage or warped
gasket surface. Place straightedge across gasket surface. Determine
clearance at center of straightedge. Measure across both diagonals,
longitudinal centerline and across the head at several points. See
Fig. 3.

Fig. 3:  Checking Cylinder Head for Warpage - Typical
This Graphic For General Information Only

         On cast cylinder heads, if warpage exceeds .003" (.08 mm)
in a 6" span, or .006" (.15 mm) over total length, cylinder head must
be resurfaced. On most aluminum cylinder heads, if warpage exceeds .
002" (.05 mm) in any area, cylinder head must be resurfaced. Warpage
specification may vary with manufacturer.
         Cylinder head thickness should be measured to determine
amount of material which can be removed before replacement is
required. Cylinder head thickness must not be less than manufacturer's
specifications.
         If cylinder head required resurfacing, it may not align
properly with intake manifold. On "V" type engines, misalignment is
corrected by machining intake manifold surface that contacts cylinder
head. Cylinder head may be machined on surface that contacts intake
manifold.
         Using oil stone, remove burrs or scratches from all sealing
surfaces.

         VALVE SPRINGS

         Inspect valve springs for corroded or pitted valve spring
surfaces which may lead to breakage. Polished spring ends caused by
a rotating spring, indicates that spring surge has occurred. Replace
springs showing evidence of these conditions.
         Inspect valve springs for squareness using a 90 degree
straightedge. See Fig. 4. Replace valve spring if out-of-square
exceeds manufacturer's specification.

ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION 

         Using vernier caliper, measure free length of all valve
springs. Replace springs if not within specification. Using valve
spring tester, test valve spring pressure at installed and compressed
heights. See Fig. 5.
         Usually compressed height is installed height minus valve
lift. Replace valve spring if not within specification. It is
recommended to replace all valve springs when overhauling cylinder
head.

Fig. 5:  Checking Valve Spring Pressure - Typical
This Graphic For General Information Only

         VALVE GUIDE

         Measuring Valve Guide Clearance
         Check valve stem-to-guide clearance. Ensure valve stem
diameter is within specifications. Install valve in valve guide.
Install dial indicator assembly on cylinder head with tip resting
against valve stem just above valve guide. See Fig. 6.

ENGINE OVERHAUL PROCEDURES - GENERAL INFORMATION 

         Lower valve approximately 1/16" below valve seat. Push valve
stem against valve guide as far as possible. Adjust dial indicator to
zero. Push valve stem in opposite direction and note reading.
Clearance must be within specification.
         If valve guide clearance exceeds specification, valves with
oversize stems may be used or valve guide must be replaced. On some
applications, a false guide is installed, then reamed to proper
specification. Valve guide reamer set is used to ream valve guide to
obtain proper clearance for new valve.

         Reaming Valve Guide
         Select proper reamer for valve stem. Reamer must be of
proper length to provide clean cut through entire length of valve
guide. Install reamer in valve guide and rotate to cut valve guide.
See Fig. 7.

Fig. 7:  Reaming Valve Guides - Typical
This Graphic For General Information Only