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.
REMOVAL & INSTALLATION
The valve guides in all engines covered in this guide may be replaced. To remove the guide(s), heat the cylinder head to 302-320°F (150-160°C). Drive out the guides using a 2 ton press (many machine shops have this equipment) or a hammer and brass drift which has been modified with washers as in the accompanying illustration.
Some valve guides are retained by snaprings, which must be removed prior to guide removal.
With the guide(s) removed, the cylinder head valve guide holes should be reamed to accept the new guides. The head should then be heated again and the new guides pressed or driven into place. On engines which utilize valve guide snaprings, install the snapring to the guide first, then install the guide into the head. Ream the new valve guide bores to 8.00-8.01mm.
Valve guides which are not excessively worn or distorted may, in some cases, be knurled rather than reamed. 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 reaming the guides should be discussed with a machinist.
Valve refacing should only be handled by a reputable machine shop, as the experience and equipment needed to do the job are beyond that of the average owner/mechanic. During the course of a normal valve job, refacing is necessary when simply lapping the valves into their seats will not correct the seat and face wear. When the valves are reground (resurfaced), the valve seats must also be recut, again requiring special equipment and experience.