How A Car Engine - Motor Works

The engine is the heart of your car, but instead of pumping
blood, the engine pumps air and fuel. The engines main function
is to convert air and fuel into rotary motion so it can drive the
wheels of the car. How does it do that ??.... Well let's start
with a cutaway of the engine and see all the major parts then we
will get into the actual mechanics.

Pistons: Most common engines have 4, 6, or 8 pistons, which move
up and down in the cylinders. On the upper side of the piston is
what is called the combustion chamber where the fuel and air mix
before ignited. On the other side is the crankcase, which is full
of oil. Pistons have rings which serve to keep the oil out of the
combustion chamber and the fuel and air out of the oil.

Crankshaft: The crankshaft is connected to the pistons via a
connecting rod. As the piston moves up and down in the cylinder
it rotates the crankshaft and converts the straight line motion
into rotary motion.

Valve train: The valve train consists of valves, rocker arms,
pushrods, lifters, and the camshaft. (shown in above picture in
blue, yellow, and green) The valve train�s only job is that of a
traffic cop. It lets air and fuel in and out of the engine at the
proper time. The timing is controlled by the camshaft, which is
synchronized to the crankshaft by a chain or belt.

Now that we have a general overview of the parts involved let's
talk about what happens. Most automotive engine today are
4-stroke (or 4-cycle) engines, meaning they have four distinct
events which make up the cycle.

Intake stroke: The camshaft opens the intake valve and the piston
moves down the cylinder. This creates vacuum and sucks in air and
fuel into the combustion chamber above the piston.

Compression stroke: As the piston starts moving back up the
cylinder the intake valve closes and seals off the combustion
chamber. The causes the air and fuel to compress.

Power stroke: As the fuel is compressed and the piston nears the
top of the cylinder the spark plug fires and ignites the fuel and
air. This explosion pushes the piston back down the cylinder and
drives the crankshaft.

Exhaust stroke: After the piston reaches the bottom of the
cylinder, the exhaust valve opens and the gasses left over from
the fuel and air are sent out to the exhaust system.
Put these four events together in the above order and you have a
complete cycle. Are you asleep yet? That's enough theory, let's
talk about the real world and problems you might encounter with
the above mentioned parts.

Pistons: Remember I talked about the rings, which seal the
combustion chamber from the crankcase. The rings over time tend
to wear out. When they wear they allow the fuel and air to enter
into the oil and dilute it. This dilution reduces the oils
ability to lubricate your engine and can cause premature wear.
Also if the rings wear down they can allow oil from the crankcase
to enter the combustion chambers. This will result in oil being
burned and exiting your tailpipe as grayish/white smoke. If your
car spews grayish white smoke and it does not go stop in the
first few minutes after start-up you might have warn rings. If
the smoke goes away after start-up look to the valve train
section.

Crankshaft: The crankshaft rides on bearings, which can wear down
over time. The bearings support the crankshaft and also the rods,
which connect the pistons to the crankshaft. A loud medium
pitched knocking noise in the engine points to warn bearings most
of the time. This is usually a costly repair and involves
removing the crankshaft and either machining the surface where
the bearings ride, or replacing the entire crankshaft. To prevent
this type of problem, use a high quality oil, change your oil at
suggested intervals (3 months or 3000 miles is a safe number) and
always maintain your oil level between oil changes.

Valve train: Remember the oil smoke problem mentioned above in
the piston sections. If your car only smokes grayish/white smoke
at start-up you may have leaking valve seals. Valve seals keep
oil from above the valve from leaking into the combustion
chamber. When they wear, they can allow oil to seep into the
combustion chamber and collect there until your start the engine
again. You generally do not get oil leaking past the valve seals
while the engine is running since the seals expand with the heat
of the engine and plug the leak.

Another common problem is the timing chain or belt will slip or
even break causing the cam shaft to stop rotating. Remember the
camshaft tells the valves when to open and if it stops spinning
then the valves stop opening and closing. No valve moving, no
engine running :-)

A term you will here when talking about timing chains and belts
is "interference engine". When an engine is an "interference
engine" the pistons and valves are so close together that if the
valves were to stop moving (broken belt or chain) and the
crankshaft kept spinning they would crash into the piston.
(that's the interference) This crash tends to do bad things to an
engine, breaking valve, bending pushrods, and even cracking
pistons. This is why most manufacturers recommend changing the
timing chain or belt every 60,000 miles. Timing belts dry out,
stretch and deteriorate over time so even if you do not have
60,000 miles on the car think about changing the belt after it's
6 years old.

Preventive Maintenance:

Change your oil regularly.

Give your engine a chance to warm up before driving if possible.
Let the oil get into all parts of the engine before driving. This
is even more critical in cooler temperatures when the oil is cold
and sluggish.

Change your timing belt or chain at your manufacturer's
recommended interval.

void "snake oil" additives advertised on late night TV. Regular
oil changes and good maintenance habits will keep your engine
running it's best.

If you have a turbo charged engine, give the engine a minute or
two cool down before turning it off. This cool down period allows
oil to circulate and cool down the bearings. If you shut off the
engine immediately after hard driving, the oil can gum up around
the hot bearings and create problems down the road.
What to discuss with your mechanic:

If you have to replace your engine, discuss the benefits of
buying used versus new. If you plan on keeping your car for some
time, a new engine might be the best bet. Sometimes new engines
are not much more expensive than rebuilt ones, and offer the best
solution.

When trying to diagnose engine noises, be as descriptive as
possible. Take note to when the noise occurs; at what throttle
position, and when the noise started occurring. Sometimes
changing the weight of oil being used can cause a new noise to
crop up. Make sure you mechanic knows if you changed oil brands
or weight recently.

Kevin Schappell maintains http://www.carbuyersclub.com where he
gives advice on buying, selling, insurance, and financing. A
mechanical engineer and car guy, Kevin has decided to spend his
online time helping others learn about automobiles. To learn more
about how your car works, Kevin has created
http://www.mycarwizard.com