Bottom Dead Center. Measured in degrees.
on both sides of the lobe. In most cases, the opening side of
the lobe being much more aggressive than the closing side. This
difference is only visible in some overhead cams.
Top Dead Center. Measured in degrees.
or round portion of the cam lobe where the valve lash adjustments
are made. A high spot in this area is called BASE CIRCLE RUNOUT.
Bottom Dead Center. Measured in degrees.
shafts that the camshafts are made from.
Top Dead Center. Measured in degrees.
a flat faced or roller companion to the camshaft that transfers
the action of the camshaft to the rest of the valve train by
sliding or rolling on the cam lobe.
is the maximum distance that the cam pushes the follower when
the valve is open. This is different from valve lift. See Gross
of the camshaft that create the valve movement.
of the cam transferred to a template or master. The master is
then installed in the cam grinding machine to generate the shape
of the lobes of the production cam.
shape of the camshaft lobe.
containing many cams that covert rotary motion to reciprocating
(lifting) motion. For every 2 revolutions of the crankshaft,
the camshaft rotates 1 revolution. The lobes on the camshaft
actuate the valve train in relation to the piston movement in
an internal combustion engine. The camshaft determines when the
valves open and close, how long they stay open and how far they
is a method to heat treat steel camshaft billets. In this method,
the camshaft is placed in a carbon gas atmosphere furnace and
heated to the proper temperature. When the shaft has absorbed
the proper amount of carbon, it is removed from the furnace and
quenched (cooled in oil) to the proper temper.
used to describe a camshaft which is made from a casting. The
material for the casting is a special grade of iron alloy called
follower made from high quality iron alloy that is heat treated
by pouring the molten iron into a mold with a chilled steel plate
at the bottom to heat treat the face of the lifter. It is compatible
with steel and hardface overlay cams only.
of the cam lobe adjacent to the base circle which lifts at a
constant slow speed. It's purpose, is to compensate for small
deflections and take up the slack in the valve train created
by the valve lash. The opening ramp takes up all clearances in
the valve train and causes the valve to be on the verge of opening.
The closing ramp begins when the valve touches the valve seat
and ends when the tappet returns to the base circle. Ramp designs
have a tremendous effect on power output and valve train reliability.
spring that has been compressed to the point where the coils
are stacked solid and there is no space left between the coils.
The valve cannot open any further when this happens.
true or having the same center. In camshaft terminology, the
cam bearings and lobes are concentric to each other when the
cam is straight and there is .001" or less runout between
all the cam lobes and bearings.
of the camshaft measured between the cam lobes.
In Your Camshaft means synchronizing the camshaft's position
with the crankshaft. A few degrees of misalignment can affect
the engine's operation dramatically.
OverHead Cam. A pair of overhead camshafts, one to operate the
intake valves and the other to operate the exhaust valves.
having different grindes on the intake and exhaust lobes. There
are various opinions on whether or not there is an increase in
performance over a single pattern camshaft. Unfortunately there
is no fair way to compare the two styles. Both types work quite
well and there is no benefit to turning down one style of camshaft
in favor of the other on this basis alone.
of time that the valve is held off the seat by the cam. This
is measured by the degrees that the crankshaft rotates. More
degrees of duration will make the engine operate in a higher
measured in degrees of crankshaft rotation from when the valve
is open .050" far until it is .050" from closing.
treating process whereby a camshaft is exposed to an open flame
and then quenched (cooled in oil).
of the cam lobe or the portion of the lobe that lies between
the nose and the base circle on either side. They are also called
the opening and closing ramps.
is obtained by multiplying the cam lift by the rocker arm ratio.
Rocker arm production tolerences can vary this figure by as much
as +/- .015".
by heating the material and quenching it in oil to give durability.
Flame hardining and Induction hardening are two methods used.
A cam follower made from high quality iron alloy. This special
alloy is compatible with cast iron billet camshafts. The entire body of the hardenable
iron lifter is hard as compared to the chilled iron lifter where
only the base is hardened.
lifters are designed to maintain zero lash in the valve train
mechanism by use the engine's oiling system to automatially adjust
the valve lash (clearance) to zero.. Hydraulic lifters do maintain
a constant pressure on the camshaft lobe, which solid lifters
do not. Their advantages include quieter engine operation and
elimination of the periodic adjustment required to maintain proper
lash as with solid valve lifters.
CAMS (CHEATER CAMS):
stock cam has stock lift and duration but the flanks are modified
so that they are faster acting. This process adds about a 5%
increase in the area under the lift curve. This means there will
be a power increase during the entire rpm range of the engine.
This type of grind works very well in engines that have fuel
injection systems that run off of manifold vacuum and are therefore
very sensitive to camshaft duration changes.
is eccentric to the cam bearings of the camshaft and transmits
a lifting motion through the valve train to operate the valves.
The design of the lobe determines the usage of the camshaft.
(i.e. street use or all out competition).
for comparison only. The figure is obtained by adding the lift
at every degree of rotation.
The distance measured in degrees between the centerline of
the intake lobe and the centerline of the exhaust lobe in the
at which the valve is fully open. For example, full intake lobe
lift at 110 deg. ATDC. full exhaust lobe lift at 110 deg. BTDC.
This camshaft was ground with 110 deg. lobe centers and is timed
straight up. It is neither advanced or retarded. Another example,
full intake lobe lift at 105 deg. ATDC. full exhaust lobe lift
at 115 deg. BTDC. This camshaft was ground also on 110 deg. lobe
centers but is advanced 5 crankshaft degrees.
is the amount by which the diameter of the front of the base
circle is different from the diameter of the rear of the base
circle. The amount of taper can be anywhere from zero to .003"
depending on the engine. If the forward side of lobe is greater
than the rear side we say that the cam has taper left (TL). If
the back side of the lobe is greater than the front side then
we say that the cam has taper right (TR). Lobe taper has a dramatic
effect on the speed of rotation of the lifter. If the lifter
does not rotate at the proper speed, premature lifter and cam
wear will occur.
lift of the valve. This lift can be determined by subtracting
the valve lash dimension from the gross valve lift figure. Rocker
arm production tolerences can vary this figure by much as +/-.015".
is a surface heat treatment which leaves a hard case on the surface
of the cam. This hard case is typically twice the hardness of
the core material up to .010" deep. This process is accomplished
by placing the cam into a sealed chamber that is heated to approximately
950 degrees F and filled with ammonia gas. At this temperature
a chemical reaction occurs between the ammonia and the cam metal
to form ferrous nitride on the surface of the cam. During this
reaction, diffusion of the ferrous-nitride into the cam occurs
which leads to the approximate .010" case depth. The ferrous-nitride
is a ceramic compound which accounts for its hardness. It also
has some lubricity when sliding against other parts. The nitriding
process raises and lowers the chamber temperature slowly so that
the cam is not thermally shocked. Because of its low heat treat
temperature no loss of core hardness is seen. Gas nitriding was
originally conceived where sliding motion between two parts takes
place repeatedly so is therefore directly applicable to solving
camshaft wear problems.
NOSE OF THE
portion of the cam lobe from the base circle with the highest
Cam Engine. A camshaft in an automotive engine that is located
in the cylinder head over the engine block rather than in the
Valve Engines. In this type of engine the camshaft is positioned
beneath the valves.
where both the intake and exhaust valves are open at the same
time when the piston is at top dead center on the exhaust stroke.
The greater the seat duration is on the intake and exhaust lobes,
the greater the overlap will be in degrees.
application whereby a nonmetallic, oil-absorptive coating is
applied to the outside surface of the camshaft. This protects
the cam lobes during the break-in period.
of adjustment for hydraulic lifters. When the clearance is removed
from the valve train the rocker arms, or adjustable pushrods,
are tightened an additional turn to "preload" the hydraulic
RATE OF LIFT:
that the valve opens and closes. Cams with a higher rate of lift
have more lobe area to provide performance gains. Also known
as ramp rate.
the cam lobe to its original shape (except slightly smaller)
when there is only minimal wear.
tappet performs the same function as the mechanical or hydraulic
tappet. However, instead of sliding on the cam face, the lifter
contains a roller bearing which rolls over the cam surface.
time in degrees of crankshaft rotation that the valve is off
of its valve seat from when it opens until when it closes.
when both the intake valve and the exhaust valve are off their
seats at the same time by the same amount.
springs have a tendency to lose their tension after being run
in an engine for certain periods of time, because of the tremendous
stress they are under. At 6,000 rpm, for example, each spring
must cycle 50 times per second. The tremendous heat generated
by this stress eventually effects the heat-treating of the spring
wire and causes the springs to take a slight drop in pressure.
which causes unpredictable valve spring behavior at high reciprocating
frequencies. It's caused by the inerita effect of the individual
coils of the valve spring. At certain critical engine speeds,
the vibrations caused by the cam movement excite the natural
frequency characteristics of the valve spring and this surge
effect substantially reduces the available static spring load.
In other words, these inertia forces oppose the valve spring
tension at critical speeds.
the speed of the engine is too great for the valve springs to
control the valve. The valves will stay open and/or "bounce"
on their seats. The clearance in the valve train created by valve
float will also cause hydraulic lifters to "pumpup"
as they try to eliminate the valve clearance.
is the clearance between the base circle of the camshaft lobe
and the camshaft follower or tappet.
of parts leading from the cam lobe to the valve.