See Figure 1
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 to be replaced.
Valve guides which are not excessively worn or distorted may, in some cases, be 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 excellent oil control. The possibility of knurling rather than replacing the guides should be discussed with a machinist.
REMOVAL & INSTALLATION
See Figures 2, 3 and 4
- Heat the cylinder head to 176-212°F (80-100 Nm), evenly, before beginning the replacement procedure.
- On models equipped with a snapring retainer: Use a brass rod to break the valve guide off above its snapring.
On the diesel engine, insert an old valve wrapped with tape into the guide. Break off the guide by rapping sharply with a hammer. Remove the guide bushing snapring
- Drive out the valve guide, toward the combustion chamber using a suitable tool.
The guides are replaced using a stepped drift. Determine the height above the boss that the guide must extend, and obtain a stack of washers, their inner diameter similar to the guide's outer diameter, of that height. Place the stack of washers on the guide, and insert the guide into the boss.
- Use the stepped installation tool and press or tap the guides into position. Ream the guides according to the size of the valve stem. Install a snapring on the new valve guide.