Valve guides should be cleaned as outlined earlier, and checked when valve stem diameter and stem-to-guide clearance is checked. Generally, if the engine is using oil through the guides (assuming the valve seals are OK) and the valve stem diameter is within specification, it is the guides that are worn and need replacing.
Valve guides which are not excessively worn or distorted may, in some cases, are knurled rather than replaced. Knurling is a process in which metal inside the valve guide bore is displaced and raised (forming a very fine cross-hatch pattern), thereby reducing clearance. Knurling also provides for excellent oil control. The possibility of knurling rather than replacing the guides should be discussed with a machinist.
- Heat the cylinder head to 176-212°F, evenly, before beginning the replacement procedure.
- Use a brass rod to break the valve guide off above its snapring. (See the illustration).
- Drive out the valve guide, toward the combustion chamber. Use a tool fabricated as described in the Engine Rebuilding information.
- Install a snapring on the new valve guide. Apply liquid sealer. Drive in the valve guide until the snapring contacts the head. Use the tool previously described.
- Measure the guide bore. If the stem-to-guide clearance is below specification, ream it out, using a valve guide reamer.