Figure 3-54.Valve rotators.
clearance between the valve stem and guide. The O ring
is a small, round seal that fits into an extra groove
cut into the valve stem. It fits on the
valve stem after the spring and
retainer. Unlike the umbrella type, it seals
the gap between the retainer and the valve stem, not the
guide and stem. It stops oil from flowing through the
retainer down the stem and into the guide.
A valve rotator (fig. 3-54) turns the valve to prevent
a carbon buildup and hot spots on the valve face.
There are two types of retainersthe
release type and the positive type. The
release type of rotator releases the
spring tension from the valve while open; this allows the
valve to rotate from engine vibration The positive
rotator is a two-piece valve retainer with a flexible
washer between the two pieces. A series of balls
between the retainer pieces roll on machined ramps,
as pressure is applied and released
from the opening and closing of the
valve. The movement of the balls up and
down the ramps translates into rotations of the valve.
Valve reconditioning includes grinding valves and
valve seats, adjusting valve tappet clearances,
installing new valve seat inserts, and
timing the valves. Together, these
operations constitute the VALVE SERVICE
necessary for smooth engine performance and
maximum power output.
To recondition valves and valve seats, first remove
the cylinder head from the engine. Once the cylinder
head is off, remove the carbon from the head, the
cylinder block, and the pistons. In cleaning the top
of the piston, you must exercise care
to prevent gouging and scratching, as
rough spots collect carbon readily and
lead to preignition and detonation during operation.
Remove the valves using a valve spring compressor.
Next, clean the valves with a wire brush or buffing
wheel (fig. 3-55). When the buffing wheel is being
used, make sure you wear proper eye protection to
prevent wire and other foreign matter from flying
into your eyes.
Be careful not to interchange the valves. Bach valve
must be replaced in the same valve port from which it
was removed. The valve stem moving up and down in
the valve guide develops a wear pattern. And, if the
valves are interchanged, a new wear pattern is
developed. This causes excessive wear on the valve
stem and guide.
To eliminate confusion, you should devise a system
to identify a valve with the cylinder from which it
was taken. The most common way to
identify valves is to
Figure 3-55.Cleaning a valve with a wire buffing wheel.