30. Cylinder Head Clean and Inspect
Valve Cleaning and InspectionImportant: Do not scratch the valve stem with the wire brush.
1. Clean the valves of carbon, oil and Varnish. Carbon can be removed with a wire brush, varnish can be removed by soaking in Parts Immersion Solvent GM P/N 12345368 or equivalent.
2. Clean the valve guides.
3. Inspect the valve stem for wear. The valve stem end may be reconditioned by grinding.
4. Follow the grinder manufacturer's instructions. Ensure the new surface is perpendicular to the valve stem.
5. Inspect the valve keeper grooves for chipping or wear. Replace the valve if chipped or worn.
6. Inspect the valve face for burning or cracking. If pieces are broken off, inspect the corresponding piston and cylinder head area for damage.
7. Inspect the valve stem for burrs and scratches. Burrs and minor scratches may be removed with an oil stone.
8. Inspect the valve stem for straightness and the valve head for bending or distortion. Use V blocks. Bent or distorted valves must be replaced.
9. Clean the deposits from the valve face. Inspect the valve face for grooving.
10. Replace the valve if the face is grooved. Valve faces cannot be machined. If worn, or damaged, the valves must be replaced.
11. The valves may be lightly lapped to the valve seats.
Cylinder Head and Gasket Surface Cleaning and Inspection
1. Inspect the cylinder head gasket and mating surfaces for leaks, corrosion and blow-by. If the gasket has failed, use the following faults to determine the cause:
1.1. Improper installation
1.2. Loose or warped cylinder head
1.3. Missing, off location or not fully seated dowel pins
1.4. Corrosion in the seal area around the coolant passages
1.5. Chips or debris in the cylinder head bolt holes
1.6. Bolt holes in the cylinder block not drilled or tapped deep enough
1.7. Other
2. Inspect the cylinder head gasket surface.
- Cylinder head may be reused if corrosion is found only outside a 4 mm (0.375 inch) band around each combustion chamber (1).
- Replace the cylinder head if the area between the valve seats is cracked (2).
- Replace the cylinder head if corrosion has been found inside a 4 mm (0.375 inch) band around each combustion chamber (3).
Important: Do not use a wire brush on any gasket sealing surface.
3. Clean the cylinder head. Remove all varnish, soot and carbon to the bare metal.
4. Clean the valve guides.
5. Clean the threaded holes. Use a nylon bristle brush.
6. Clean the remains of the sealer from the plug holes.
7. Replace all suspect bolts.
8. Inspect the cylinder head for cracks. Check between the valve seats and in the exhaust ports.
Important: Do not attempt to weld the cylinder head, replace it.
9. Inspect the cylinder head deck for corrosion, sand inclusions and blow holes.
10. Inspect the cylinder head deck surface for flatness.
Maximum Cylinder Head Deck Warpage Maximum Warpage: 0.05 mm (0.0020 inch)
11. If the Warpage is greater than the maximum allowed, replace the cylinder head.
12. Inspect all the threaded holes for damage. Threads may be reconditioned with thread inserts.
13. Inspect the sealing surfaces.
14. Inspect the cylinder head intake manifold surface for flatness.
Maximum Cylinder Head Intake Surface Warpage
Maximum Warpage: 0.05 mm (0.0020 inch)
15. If the Warpage is greater than the maximum allowed, replace the cylinder head.
16. Inspect all the threaded holes for damage. Threads may be reconditioned with thread inserts.
17. Inspect the sealing surfaces.
18. inspect the cylinder head exhaust manifold surface for flatness.
Maximum Cylinder Head Exhaust Surface Warpage
Maximum Warpage: 0.05 mm (0.0020 inch)
19. If the warpage is greater than the maximum allowed, replace the cylinder head.
20. Inspect all the threaded holes for damage. Threads may be reconditioned with thread inserts.
21. Inspect the sealing surfaces.
Valve Guide Reaming Valve and Seat Grinding
- Tools Required
- d 37968 Valve Guide Installer
- J 37971 Valve Guide Reamer
Valve Grinding and Valve Guide Inspection and Replacement
1. Use a caliper gauge and measure the inside diameter of the valve guide bushing. Standard Valve Guide Bushing
Inside Diameter 5.485 - 5.510 mm (0.2159 - 0.2169 inch)
2. Use a micrometer and measure the outside diameter of the valve stem.
- Standard Intake Valve Stem Diameter
5.465 - 5.480 mm (0.2152 - 0.2157 inch)
- Standard Exhaust Valve Stem Diameter
5.440 - 5.455 mm (0.2142 - 0.2148 inch)
3. To obtain the valve guide bushing oil clearance, subtract the valve stem outside diameter measurement from the valve guide bushing inside diameter measurement.
- Standard Intake Valve Oil Clearance 0.005 - 0.045 mm (0.0002 - 0.0018 inch)
- Standard Exhaust Valve Oil Clearance 0.030 - 0.070 mm (0.0012 - 0.0027 inch)
- Maximum Intake Valve Oil Clearance 0.07 mm (0.0027 inch)
- Maximum Exhaust Valve Oil Clearance 0.09 mm (0.0035 inch)
4. If the clearance is greater than the maximum specified, replace the valve and the valve guide bushing.
5. Use a J 37968 and a hammer and tap the valve guide bushing out of the cylinder head.
6. Use a J 37968 and a hammer and tap the new valve guide bushing into the cylinder head.
7. Install the valve guide bushing to the specified protrusion height of 11.5 mm (0.45 inch).
8. Use a J 37971 and ream the valve guide bushing to obtain the standard specified clearance between the valve guide bushing and valve stem.
9. Standard Intake Valve Oil Clearance 0.005 - 0.045 mm (0.0002 - 0.0018 inch)
10. Standard Exhaust Valve Oil Clearance 0.030 - 0.070 mm (0.0012 - 0.0027 inch)
11. Reconditioning the valve seats is very important.
12. Recondition valve seat after reaming the valve guide bores.
Important: Because the valve guide serves to support and center the valve grinder, it is essential that the valve guide is cleaned properly. If the valve guide requires reaming, this must be done first.
13. Inspect the valve seats for excessive wear and burned spots. Valve seats may be reconditioned by grinding. If grinding results in the new seat being too wide it may be narrowed by using a 20 degree or 70 degree stone. The 20 degree stone will lower the seat and the 70 degree stone will raise the seat.
14. The valves must seat perfectly for the engine to deliver optimum power and performance.
15. Cooling the valve heads is another important factor. Good contact between each valve and its seat in the cylinder head is necessary to insure that the heat in the valve head is properly carried away.
16. Regardless of what type of equipment is used, it is essential that the valve guide bores are free from carbon or dirt to ensure the proper centering of the pilot in the guide.
The valve seats should be concentric to within 0.05 mm (0.031 inch) total indicator reading.
17. Replace any valve that is not in serviceable condition.