The engines covered in this guide use integral valve guides; that is, they are a part of the cylinder head and cannot be replaced. The guides can, however, be reamed oversize if they are found to be worn past an acceptable limit. Occasionally, a valve guide bore will be oversize as manufactured. These are marked on the inboard side of the cylinder heads on the machined surface just above the intake manifold.
If the guides must be reamed (this service is available at most machine shops) then valves with oversize stems must be fitted. Valves are usually available in 0.001 in., 0.003 in. and 0.005 in. stem oversizes. Valve guides which are not excessively worn or distorted may, in some cases, be knurled rather than reamed. Knurling is a process which the metal on the valve guide bore is displaced and raised, thereby reducing clearance. Knurling also provides excellent oil control. The option of knurling rather than reaming valve guides should be discussed with a reputable machinist or engine specialist.