Valve Guide Service
Servicing of
valve guides is an important, but often neglected, part of a good valve job. The guide
must be clean and in good condition before a good valve seat can be made. Valve guide wear
is a common problem; it allows the valve to move sideways in its guide during operation.
This can cause oil consumption (oil leaks past the valve seal and through the guide),
burned valves (poor seat to valve face seal), or valve breakage.
There are
several satisfactory methods of checking for valve guide wear. One procedure for checking
valve guide wear is to slide the valve into its guide. Full it open approximately 1/2
inch, then try and wiggle the valve sideways. If the valve moves sideways in any
direction, the guide or stem is worn Another checking procedure involves the use of a
small hole gauge to measure the inside of the guide and a micrometer to measure the valve
stem; the difference in the readings is the clearance. Check the manufacturer's manual for
the maximum allowable clearance. When the maximum clearance is exceeded the valve guide
needs further servicing before you proceed with the rest of the job.
Servicing
procedures depend on whether the guide is of the integral or replaceable type. If it is
the integral type, it must be reamed to a larger size and a valve with an oversize stem
installed. But if it is replaceable, it should be removed and a new guide installed
KNURLING of
the valve guides has become more popular as a method of compensating for wear of the valve
guides. Knurling is accomplished by attaching a special tool to an electric drill and
inserting the tool in the worn guide. This method is not recommended if the guide has been
worn excessively or knurled previously.
Valve guides
should be removed and replaced with special drivers (fig. 3-59). When working on a valve in the
cylinder head of an engine, you may use an arbor press to remove and replace the valve
guides.
After the
valve guides are serviced and the valve seats are ground, check the concentricity of the
two with a valve seat dial indicator (fig. 3-60). Any irregularity in the seat will
register on this dial. |
