Cylinder Head and Valves

GENERAL INFORMATION

Thorough cleaning of the cylinder head and valvetrain components, followed by inspection, will help determine the scope of valvetrain repair work. Warning: If the engine has frequently overheated, the cylinder head may have warped. Carefully check the head for signs of distortion.

Cleaning

PROCEDURE

1. Clean the cylinder head mating surfaces.

2. Clean carbon deposits from the combustion chambers, all holes and passages, then wash the cylinder head with solvent.

3. Remove heavy carbon deposits from the valves.

Inspection Warning: Before deciding whether components need resurfacing, be sure to perform all of the inspection procedures described below.

CYLINDER HEAD

PROCEDURE

1. Carefully inspect the head for cracks, signs of coolant leakage and other damage. If cracks are found, replace the cylinder head.

2. Check the cylinder head mating surface for distortion. If the mating surface is warped, resurface the head. If distortion is such that the head height after resurfacing would be less than the specified minimum, replace the head.

3. Check the condition of the valve seats. If pitting, cracks or burn marks are present, the head must be repaired at an automotive repair shop. Minor defects can be removed by lapping the valve.

4. Check valve guide wear. Insert the valve into its guide and rock it from side to side. A small, barely noticeable amount of play is acceptable.

5. If valve play in the guide is excessive, measure the valve stem diameter. If the stem diameter has noticeably decreased due to wear, replace the valve. If the stem diameter is within specification, the valve guide must be replaced (performed at an automotive repair shop).

6. If guide bushings are replaced, the valve seats should be ground (or re-cut) only after installing the new bushings.

VALVES

PROCEDURE

1. Inspect the valves for cracks, signs of burning, scoring and a shoulder formed by wear on the stems. Check the valve for bending by rotating it. Check the face wear. If any signs of wear or damage are found, replace the valve.

2. If the valve condition is satisfactory after this inspection, measure the valve diameter at several points. A noticeable difference in diameters indicates stem wear. If a noticeable difference in diameter is found in at least two places, replace the valve.

3. If the valves are in satisfactory condition, lap them to the seats. If the seats have only minor damage, or the seat has been ground, lapping can be performed with fine compound. Coarse lapping compound should be used only if deep wear or severe burning of the seats is found. In this case, the cylinder head and valves should be taken to a qualified specialist to determine whether the seats should be re-cut or the seat inserts replaced (if provided).

4. Before lapping, place the cylinder head on a flat surface with the combustion chambers facing up.

5. Apply a thin layer of lapping compound to the seat face. Perform lapping by rotating the tool 180° in both directions and periodically lifting the valve to evenly distribute the abrasive.

6. Coarse lapping is complete when a uniform matte band forms on the valve and seat faces. Wipe the valve and seat clean of compound and continue lapping with fine compound. Lapping is complete when a uniform continuous grey band forms on the valve and seat faces. Do not lap further, as excessive removal of the seat may make subsequent repair impossible.

7. After all valves have been lapped, thoroughly clean all parts with solvent.

VALVE TRAIN COMPONENTS

PROCEDURE

1. Inspect the springs for chipping and damage. A rough check of the spring condition can be made by comparing the free length of the spring with the specification.

2. Check the spring tilt from vertical using a square and compare with the specification.

3. If at least one spring is damaged, exceeds the tilt limit from vertical, or has lost tension, replace all springs as a set. Note that during an overhaul, valve springs are recommended to be replaced regardless of their condition.

4. Valve stem seals must be replaced regardless of their condition.