An engine is part of every car and truck on the planet. Whether the engine is
gas powered or electric your vehicle would not move if not for the engine. Gas
powered engines come in two varieties, gasoline or diesel. Both are remarkably
similar with the only real difference being the compression ratio and the ignition
system which ignites the fuel inside the combustion chamber. Let's start deep
inside the engine at the heart of where the power is made, the combustion
chamber. This chamber is made up of a piston, engine cylinder encapsulated
within the engine block, a
head along with intake and exhaust valves. While the piston is headed
downward in the cylinder a charge of emulsified fuel is sent into the combustion
chamber via the
Once this happens the piston will start to travel upward in the cylinder bore
while the intake valve closes. This seals the combustion chamber so the piston
compression as it heads upwards which is then ignited by the ignition system
when the piston is near the top of its travel. This causes the fuel/air charge
to ignite causing an explosion which drives the piston downward which creates
the power. In the guide below we will show you each piece of the engine
and how the power is delivered to the transmission which is then connected to
the rear or front wheels.
Here is a video of an engine in action so you can get an idea of what goes on
inside the engine while it is running. This video shows each cycle of the
process; intake, compression, combustion and exhaust. It takes the piston two
upward and downward strokes to complete a cycle which is why we call it a four
Watch the Video!
What Goes Wrong?
The engine deals with an incredible amount of force and heat with each thrust
of the piston. There are several supporting systems that must be in good working
order such as the oiling and
to keep the engine going.
Also, there is a variety of fast moving internal moving parts that are put
through the stress and strain of being pushed and pulled at extreme pressures.
When there is a minor internal problem such as with a valvetrain parts such as a
cam follower it could result in a
ticking or clicking noise along with a
cylinder misfire. When more extreme failures occur such as a piston or rod
failure it can cause the engine to have a more serious problem such as major
vibration or the engine will lock up entirely.
What Does It Cost?
When an engine fails there are three ways to address the problem all in which will have difference costs associated with them. When the engine has a problem the
first step is to assess the damage and what possible scenarios could accompany
such repairs. For example; the engine has dropped a valve seat from the cylinder
head and it has caused a valve to stay open which then contacts the piston. One diagnosis could be
to remove the head and fix the valve. The additional repair that should be
thought of is what about the piston it contacted and to what degree of damage
did it cause? In some cases there is minor damage which will cause no further
problems while in other cases the ring has been compromised on the piston which will
require further disassembly to fix with an additional cost as well.
If the engine has
simply worn out or is damaged to the point of replacement then a new, rebuilt or
used engine can be installed. These costs will dramatically vary due to
manufacturer and how together the engine is when it arrives for installation
such as intake and exhaust manifolds. For a typical car engine replacement you can
expect to pay between $1,400.00 to $2,500.00 (US) for labor and between $2500.00
and $5,000.00 (US) for a factory rebuilt engine. Used engines will cost less
between $800.00 and $1,800.00 (US). If you decide to go with used the labor the
remove the engine in case it is defective is generally not covered so it's a
good idea to get an engine with low miles on it.
Let's Get Started
1. Combustion Chamber
In the image below is a combustion chamber (cutaway) and is where the fuel air mixture is
compressed and ignited. In the lower center you can see the piston and piston rings as they travel upward
and downward inside the cylinder bore. The intake and exhaust valves are in the
upper section along with the spark plug electrode which is where the spark is
generated for ignition of the flammable air/gas mixture. This is also a good
look at the intake and exhaust valves and ports. Many engines have two intake and two exhaust
valves to help the engine's performance.
2. Pistons and Cylinder Bore
Here is a cutaway image of a V8 engine that shows how the pistons are
attached to the crankshaft which rotates inside of the engine block along with the cylinder heads
bolted to the top of the block deck. A straight six, five or four cylinder has just
one cylinder head.
3. Piston Connecting Rods
In this image we show how the piston is attached to the crankshaft using a
piston or connecting rod. This rod has a cap located at the bottom of the rod
which splits into two pieces so it can be bolted to the crankshaft using two rod
bolts. (It is difficult to see the line where the rod cap separates.) This is were the rod bearing is located which allows the crankshaft to
turn while being oiled by the oil pump and oiling system. At the top of
the rod there is a wrist pin that is located through the piston and can pivot
near the bottom of the piston body.
The crankshaft is where all of the pistons and rods are connected too and is
the part that is bolted to the flywheel and transmission. All of the power the
engine creates is transmitted though the crankshaft which sits in the lower
middle of the engine block. It is held in place by the use of main bearing caps
that are bolted to the block which house the main crankshaft bearings. These bearings are
also lubricated by the engine oil and the oiling system. The front of the crankshaft
protrudes outward from the engine to provide power to turn the cars accessories
such as the
conditioner. The rear of the crankshaft exits the back of the engine to
connect to the
flywheel and then the
transmission to provide power for the car. Oil leaks are controlled by a
main seal and a
rear main seal.
5. Main Bearings and Engine Block
Here are what the engine main crankshaft bearings look like when the crankshaft
is removed. In the image below is an example of one half
or the bearing. The remaining half is located in the bearing cap which bolts to
the engine block. The piston rod bearings look the same except they are a little
smaller in size. You can see a hole in the middle of the bearing which is where
motor oil is provided for lubrication.
6. Camshaft and Cylinder Head
A camshaft is a long cylindrical metal shaft that is made with very specific
lobes that are designed to open and close the intake and exhaust valves which are
in time with the piston position. This shaft is located in the
head or engine block depending on the engine's design. This important part
of the engine is what controls the intake and exhaust gasses from entering and
leaving the combustion chamber during the combustion processes. In this image the
cylinder head has been partially removed so you can see how the camshafts work
with the valves.
Here is a cutaway of a cylinder head which shows the intake and exhaust ports
which are controlled by the valve in each port. These valves seal the combustion
chamber so when the piston is travelling upward it can create compression for the
7. Timing Chain or Belt
A timing chain or belt is used to turn the camshafts which open and close the
valves. This chain or belt is designed to keep the camshaft in perfect
correlation with the crankshaft and turns the camshaft one time for every two
times the crankshaft turns. This chain or belt runs from the crankshaft to the
A tensioner is used to keep the slack out of the timing chain or belt which
is necessary to hold the chain or belt from jumping time while the engine is
running. The timing chain or
belt is driven at the crankshaft
using a drive gear near the front main seal and
Where It All Starts
8. Throttle Bore
The engine is basically a large air pump that burns fuel. The process begins
at the throttle bore which is connected to the intake manifold. This is where
the engine air is regulated. The engine speed and power is controlled by this
device which opens to allow more air inside creating additional
power and then closes to shut the power down. This air flow is monitored by the
mass air flow sensor and cleaned by the
9. Intake Manifold
Once air has passed through the throttle
actuator it enters the intake manifold where it is divided and separated among individual cylinder
intake ports within the cylinder head. The air is then controlled by the intake valve. This manifold bolts directly onto
the cylinder heads and can be made of plastic or aluminum.
10. Fuel Injector
fuel injector is used to control and meter the amount of fuel that enters
the engine at any given time. While the engine is under load and more power is
needed a command for more fuel is given by the car's
computer (PCM). The fuel injector is part of the
injection system. In the image below there is a set of direct injection fuel
injectors which spray fuel directly into the combustion chamber near the time of
ignition unlike the traditional fuel injectors which spray into the intake port
just behind the intake valve.
11. Ignition Coil
After the fuel air mixture is compressed
an ignition coil supplies a high voltage, low amperage charge to the
spark plug. This process
is also controlled by the cars computer which gains reference to each pistons
position using a
crankshaft angle sensor.
12. Oil Pump
An oil pump is used to pick up oil from the oil pan and pump it throughout the
engines internal moving parts. This pump can be driven by a variety of ways,
this particular pump is driven by a chain at the front of the crankshaft. The
oil pump determines the amount of oil pressure the engine will have using a
pressure spring fitted into a relief valve of the pump.
Engine coolant is used to help keep the engine cool
while running by using the
This coolant is circulated inside the engine block and cylinder heads to keep the
engine's heat from causing internal damage. A water pump is used to move the coolant into
to be cooled and then transferred back into the engine so the process can start
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