place them on a piece of board with holes drilled and
numbered to correspond with the cylinder each valve
The next step is to resurface the valve face. This is
done by using a valve grinding or refacing machine.
VALVE GRINDING is done by machining a fresh,
smooth surface on the face and stem tips. Valve faces
suffer from burning, pitting, and wear caused by
opening and closing millions of times during the service
life of the engine. Valve stem tips wear because of
friction from the rocker arms.
Although there are some variations in design, most
valve grinding machines (fig. 3-56) are basically the
same. They use a grinding stone and a precision chuck
to remove a thin layer of metal from the valve and stem
tip. The following steps are used in preparing to reface a
DRESS THE STONE by using a diamond
cutter to true stone surface (fig. 3-57). Do this
before grinding the valves. A diamond-tipped
cutting attachment is provided with the machine
for truing the stone.
Follow the equipment
manufacturers instructions for that specific
Be careful when using a diamond tool to dress
a stone. Wear eye protection and feed the
diamond into the stone SLOWLY. If fed too
fast, tool or stone breakage may result.
The chuck must NOT clamp onto an
unmachined surface or runout will occur.
SET THE CHUCK ANGLE by rotating the
valve grinding machine chuck assembly. An
interference angle (normally 1 degree
difference in valve face angle and valve seat
angle) is set on the machine. If the valve seat is
Figure 3-57.Stone dresser.
45 degrees, the chuck is set to 44 degrees. This
allows for reduced break-in and sealing time.
CHUCK THE VALVE in the valve grinding
machine by inserting the valve stem into the
chuck Make sure the stem is inserted so the
chuck grasps the machine surface nearest the
Before grinding, inspect each valve face for
burning and each stem for wear. Replace valves that are
badly worn or burned. Grind a new valve along with the
old, used valves.
Wear a face shield when grinding valves. The
stone could shatter, throwing debris into your
To grind the valve face, turn on the machine and
cooling fluid SLOWLY feed the valve into the stone.
While feeding, slowly move the valve back and forth in
front of the stone. Use the full face of the stone but do
NOT let the valve face move out of contact with the
stone while cutting. Grind the valve only long enough
to clean up its face. When the full valve face looks shiny
with no darken pits, shut the machine off and inspect the
Figure 3-56.Valve-refacing machine.