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What does “four cylinder” mean anyway?
When you talk about cars, “cylinders” comes up often. Four-cylinder usually comes up with smaller
cars and is thought to be economical but not exactly powerful. Eight-cylinder comes up around men’s wagging
tails and is usually associated with power and speed. But what exactly is a cylinder and what does
it do for the car?
Long story short, a combustion engine
works by pushing gas into a chamber - you guessed it- the cylinder, mixing it
with air and then blowing it up. Now
don’t panic, the car is not going to blow up. These explosions are tiny and expertly timed
(that’s another article) to make the engine work. This process repeats over and over as the
cylinders move up and down. The process can be broken down into four
Intake: Inside the cylinder is a piston. The piston strokes down on a rack that moves
kind of like a bicycle pedal. The
downward movement draws the air and fuel into the cylinder. At the bottom of the stroke, the valve
closes, holding the air and fuel inside.
Compression: The piston then strokes up in the cylinder
and compresses the mixture according to the compression ratio of the
engine. Ratios range from 8:1 to 10:0
for the most part, meaning the mix is getting squashed to a tenth of it’s
original volume. Ratio varies, but the
point is it's getting tight in there.
Power: The fun part.
At the top of the cylinder there’s a spark plug which does just that:
sparks. The spark ignites the gas and
the explosion makes the compressed mixture get lots bigger. The expansion of the vapor creates enough
force when it pushes the piston down the cylinder that it turns the crank shaft
to move the car.
Exhaust: The clean-up.
If you behaved like I did as a child, you know blowing things up makes a
bit of a mess. Vapor is no
different. Your cylinder is now full of
burned gas, aka exhaust. When the piston
is at the bottom of the cylinder, the exhaust valve opens letting the exhaust
out to the exhaust system. This is super
pressurized and loud as it rushes out, sort of like the
car version of a loud fart, warranting the muffler on the exhaust system. As the piston moves up the cylinder, it
chases out the remaining exhaust in preparation to start the whole thing over
This happens in each cylinder, each
at a different time. This is the firing
order. Firing order and timing are a
whole other topic, but the Reader’s Digest version is:Each cylinder will have
fired once to turn the crank shaft two times.
So more cylinders, more “pushes” per turn. Not faster, but more oomph. This is what burns your gas, so fewer
cylinders may mean better fuel economy, dependent on factors such as
weight. Obviously, it takes more power
to push an older car made of heavy steel than a car made of newer, lighter
The Dreaded Timing Belt
So you’re sitting in the waiting room, catching up on issues of magazines you would never order for yourself when your mechanic steps out from the mysterious back shop and says you need a new timing belt. You don’t know what this is but you know by the price he just quoted you, they’re definitely proud of it. You may not have noticed a problem. Perhaps you came in for something else. And you may have heard stories about shady shops recommending work you don’t need in an effort to add items to the bill. So do I really need one? Or does my mechanic’s kid need braces? Well, what is it and why? A timing belt is a rubber belt with teeth that goes along one side of your engine to keep the crank and camshafts timed properly.
In English, it’s part of a system that keeps the top half of the engine- cylinder head, valves- synchronized with the bottom half- crankcase, pistons (thanks for the simplification, Freddy “Tavarish” Hernandez). If you have a car that’s from the 90’s or before, you likely have a timing belt. Newer cars from certain manufacturers will have them still, but some have changed over to a timing chain which, in theory, lasts longer. Great, but I didn’t notice a problem. Why would I need a new one? You wouldn’t necessarily have any warning from the car if a timing belt is “going bad.” If it’s already broken, your car won’t start. If it’s on the way out, sometimes a squeak or an odd noise might give it away. If you were in for an oil change, a mysterious noise, or a service light from the dash, your mechanic may have noticed cracks on the belt or worn teeth that made him sound the alarm or he may be checking your mileage. Belt lifespan varies from model to model. At minimum, they’ll give you 60,000; some will double that and most will fall somewhere in between. Depending on your manufacturer recommendations, if you’re at 105,000 and you stare blankly at the tech when he asks if your belt has been changed, he’s likely going to recommend replacement. Even if you agree the belt needs to be changed, you have that dirty, four-letter word to contend with: COST. Parts are generally nothing special for this task, ranging from $150 to $250 in the most common models, even though certain models can be higher. What can often be misconstrued as fighting words is the labor cost. Also highly variable, labor could range from $170 to $600 or more.
The major factor is accessibility. To access the timing belt, you may be removing accessories, an engine timing cover, the water pump, pulleys, tensioners—no biggie if you have space to work under the hood but an unholy nightmare taking many labor hours if you’re poking around a V6 sedan with no easy access to inner parts. But that’s several hundred dollars I’m not prepared to part with yet. Do I really have to? No, the only things we have to do are pay taxes and die. Talk to your mechanic.
Cracks in the belt may not necessarily mean it’s bad. It could carry you a couple thousand more miles until you can sock away the cash. However, if your mechanic is particularly concerned for it’s condition, you may want to bite the bullet. No sense adding a tow bill and missing a morning of work to a project that’s already potentially costly.
A timing belt is the ribbed belt that is placed in a specific configuration along one side of your engine to keep the crank and camshafts timed properly basically it keeps the top half of the engine in sync with the bottom. If you have an older car from the 90s and below odds are you have a timing belt. Some new car manufacturers, such as Audi, still use timing belts in their engine designs but for longevity many manufacturers have switched to metal timing chains. It’s best to replace your timing belt every 60,000 miles or every 5 years.
A four stroke engine requires that the valves open and close once every other revolution of the crankshaft. The timing belt does this. In some engine designs the timing belt may also be used to drive other engine components such as the water pump and oil pump. Chains and gears may be more durable, rubber composite belts are quieter in their operation are less expensive, more efficient, by dint of being lighter, when compared with a gear or chain system.
An Indicator that the timing chain may need to be replaced includes a rattling noise from the front of the engine. The usual failure modes of timing belts are either stripped teeth or delamination and unraveling of the fiber cores.