engines. Carbon deposits, incidentally, tend to pit the
emergency, you can use a long screwdriver or a piece of
softer metal of the cylinder block and head.
garden hose. You should always be careful of the
moving fan belt and fan blade.
Many engines have replaceable valve seat inserts
(fig. 3-44) made of special heat-resistant alloys. These
Usually, where noise exists in one or more of the
inserts can be used in either cast-iron or aluminum
valve lifters, all lifter units should be removed, cleaned
blocks or heads. When a valve seat insert is badly worn
in a solvent, reassembled, and reinstalled in the engine.
from grinding or pitting, it must be replaced.
If dirt, carbon, or the like, is present in one unit, it is
more than likely present in all of them; and it is only a
RECONDITIONING VALVES AND VALVE
matter of time before the other lifter units will cause
SEATS.--Valve reconditioning includes grinding
valves and valve seats, adjusting valve tappet
Parts of hydraulic valve lifters are not inter-
clearances, installing new seat inserts, and timing the
changeable. Should one part become damaged, it is
valves. Together, these operations constitute the valve
necessary to replace the whole unit. The plunger must
service necessary for smooth engine performance and
be free to move in the lifter body. A simple test for this
maximum power output.
is to be sure that the plunger will drop of its own weight
in the body.
around the shop. It is the major, but not the only,
ENGINE VALVES AND VALVE SEATS.--
operation in reconditioning them. Before valves are
Most engines have poppet valves (also called
ground or refaced on the valve-refacing machine, they
mushroom or tulip valves). The word "poppet" comes
must be cleaned. Heavy carbon deposits and
from the popping action of the valve; "mushroom" and
excessively burned valves may indicate the need for
"tulip" come from the shape of the valve. The intake
new rings or valve guides and/or intake valve oil seals.
valves are ordinarily made of chromium-nickel alloy.
Carbon deposits and burned valves may also indicate
The exhaust valves are generally made of silichrome
alloy because of the extremely high temperatures they
ignition in the gasoline engine or improper fuel
must withstand. Sometimes exhaust valves contain
injection in the diesel engine.
sodium in a sealed cavity extending from head to stem.
To recondition valves and valve seats, first take off
This sodium cools the valves by conducting heat away
the cylinder head and remove the carbon from the head,
cylinder block, and pistons. In cleaning the top of the
Both the intake and the exhaust valves operate
pistons, you must exercise care to prevent gouging and
against the rims of circular openings (valve ports) in the
scratching, as rough spots collect carbon readily and
combustion chambers of the cylinders. These rims are
will lead to preignition and detonation during engine
called valve seats (fig. 3-43). The valve and valve seat
operation. Remove the valves by using a valve spring
must make perfect contact. Although some earlier
engines were designed with flat contact surfaces for the
valve and valve seat, most are now designed with valve
seat angles of 30 to 45 degrees, as shown in figure 3-43.
This angle helps prevent excessive accumulation of
carbon on the contact surface of the seat, a condition
that keeps the valve from closing properly. To further
degree between the valve and seat, is used on some
Figure 3-44.--Valve seat insert.
Figure 3-43.--Valve head and set angle.