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Universal Joint
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The Universal joint (U-joint) connects the drive shaft to the transmission
output shaft and the differential pinion gear shaft. This joint must be
flexible enough to allow changes in the driving angle (road incline) and the
drive shaft. This way, the torque is constantly transmitted when the rear axle
is moving up and down. Smaller U-joints are used to route the turning motion of
the steering wheel through the steering column to the steering box. There are
two types of U-joints, the cross and roller type and the ball and trunnion
type. The cross and roller type is used the most; it allows the drive shaft to
bend. The ball and trunnion type less frequently used; it allows the drive
shaft to bend and also permits backward and forward motion of the drive shaft.
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Vacuum Hoses and Motors |
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Vacuum lines are a series of hoses, or tubing, to the intake manifold. These
hoses supply vacuum to various components of the engine, such as the emissions
control system. Most air conditioning systems have vacuum motors to open and
close the doors on the air conditioning ducts. A vacuum motor is just a small
diaphragm with connecting rods to activate the valves of the system. They have
the advantages of simplicity and quietness. |
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Vacuum Pump |
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Most of the fuel pumps have a vacuum booster section that operates the
windshield wipers at an almost constant speed. The fuel section then functions
in the same way as ordinary fuel pumps. One difference is that the rotation of
the camshaft eccentric in the vacuum pump also operates the vacuum booster
section by actuating the pump arm, which pushes a link and the bellows
diaphragm assembly upward, expelling air in the upper chamber through its
exhaust valve out into the intake manifold. On the return stroke of the pump
arm, the diaphragm spring moves the bellows diaphragm down, producing a suction
in the vacuum chamber. The suction opens the intake valve of the vacuum section
and draws air through the inlet pipe from the windshield wipers. When the
wipers are not operating, the intake manifold suction (vacuum) holds the
diaphragm up against the diaphragm spring pressure so that the diaphragm does
not function with every stroke of the pump arm. When the vacuum is greater than
the suction produced by the pump, the airflows from the windshield wiper
through the inlet valve and vacuum chamber of the pump and out the exhaust
valve outlet to the manifold, leaving the vacuum section inoperative. With high
suction in the intake manifold, the operation of the wiper will be the same as
if the pump were not installed. When the suction is low, as when the engine is
accelerated or operating at high speed, the suction of the pump is greater than
that in the manifold and the vacuum section operates the wipers at a constant
speed. |
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Valve Cover |
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The valve cover covers the valve train. The valve train consists of rocker
arms, valve springs, push rods, lifters and cam (in an overhead cam engine).
The valve cover can be removed to adjust the valves. Oil is pumped up through
the pushrods and dispersed underneath the valve cover, which keeps the rocker
arms lubricated. Holes are located in various places in the engine head so that
the oil recirculates back down to the oil pan. For this reason, the valve cover
must be oil-tight; it is often the source of oil leaks. One way to determine if
your valve cover is bent is to remove the gasket and put the valve cover back
on to the cylinder head. When the valve cover and cylinder head come into
contact, the cover should sit flat. If it rocks, it is bent. A symptom of a
bent or leaking valve cover is a pinching of the valve cover gasket. This means
that the gasket is sealing one area and not sealing another area. This
condition produces a leak; oil could be leaking down the side of the engine.
Some valve covers are hard to access, because they are covered with other
engine parts. Chronic valve cover leakage can sometimes be fixed by using two
gaskets glued together instead of using just one. |
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Valve Lifter |
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The valve lifter is the unit that makes contact with the valve stem and the
camshaft and rides on the camshaft. It opens the valve when the cam lobes push
it upwards. The engine oil comes into the lifter body under pressure. It passes
through a little opening at the bottom of an inner piston to a cavity
underneath the piston. The oil forces the piston upward until it contacts the
push rod. When the cam raises the valve lifter, the pressure is placed on the
inner piston, which tries to push the oil back through the little opening. It
can't do this, because a small check valve seals the opening. When the cam goes
upward, the lifter solidifies and lifts the valve. Then, when the cam goes
down, the lifter is pushed down by the push rod. It adjusts automatically to
remove clearances. |
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Valve Ports |
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Valve ports are openings in the cylinder head. Intake ports let the fuel
mixture into the cylinder head, and exhaust ports let the exhaust out. |
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Valve Seals |
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The valve seal is a unit that goes over the end of the valve stem. It keeps
excess oil from getting between the valve guide and the valve stem. |
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Valve Springs |
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The valve springs keep the valves closed tightly against their seats until the
cam opens the valve. After the cam turns (releasing pressure), the valve
springs close the valves. |
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Valves |
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The valve opens and close the valve ports. If the ports were always open, the
fuel exploded in the combustion chamber would leave through the ports. The
explosion has to be kept in the combustion chamber to push the piston down. The
valves are set up to open and close at exactly the right moment. One lets the
fuel mixture in and closes. After the fuel explodes and pushes the piston down,
the other valve lets the exhaust out. |
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Visor |
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The visor is a flat sunshade and is usually movable. It is attached to the
interior of the car at the top of the windshield. Visors protect the eyes of
the driver and passengers from the sun's glare. |
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Voltage Regulator |
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The voltage regulator controls voltage and current output of the alternator by
automatically cutting resistance in or out of the field circuit to keep it in a
safe value. Varying the resistance alters the amount of current passing through
the field. When the battery becomes fully charged, the resistance is cut into
the field circuit and the charging rate is decreased. In electromagnetic
regulators, the voltage regulator unit limits voltage output by controlling the
amount of current applied to the rotating field. The field relay on these
regulators connects the alternator field windings and voltage regulator
windings directly to the battery. The conventional cutout relay unit has been
eliminated by the diodes in the alternator. The current regulator has also been
eliminated by the current-limiting characteristic of the alternator design.
Basically, in a transistorized or an electronic regulator, the transistor is
switched on and off to control the alternator field current. The frequency of
switching depends on the alternator speed and accessory load, with the
possibility that the on-off cycle may be repeated as often as 7000 times per
second. The transistorized units have a voltage limiter adjustment. The
electronic units are factory calibrated and sealed. They are also
nonadjustable. |
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