Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Valve Rotator: Service and Repair
Fig. 20 Valve rotator & retaining components
The parts involved in the rotating mechanism, Fig. 20, are a special spring seat retainer, a pair of flat half-moon keys, a close fitting cap located on the
valve stem and a specially constructed valve stem.
In order to accommodate valve expansion, the valve lash must be maintained. When camshaft rotation causes this lash or clearance to be taken up, the
cap on the valve stem causes the valve keys to raise the spring retainer, removing the load on the valve springs from the valve before the valve is moved
from its seat. A clearance of .002---.004 inch should be maintained between the end face of the valve stem and cap. This is the distance the spring
retainer is moved before the valve is moved. The slow valve rotating motion is caused by the vibration of the valve, the flowing of exhaust gases around
the valve head, and a slight rotating motion imparted to the valve by the valve spring.
Whenever valve work is being done, a check for clearance should be made by holding the assembled valve and rotating mechanism in the hands. With
one hand, press down on the valve cap and turn the valve with the other hand. If the valve turns readily, it indicates that there is clearance present.
A special gauge is available to check this clearance. If the gauge indicates no clearance, grind off the end of the valve stem. If the clearance is too
great, grind off the open end of the valve cap.
