May 4th, 2010 admin
Introduction To Camshafts
If you’re unfamiliar with camshafts, you’re in for a treat. Maybe you’ve overheard mechanics talking about them, and you know they have something to do with car engines, but that’s about it. Well fear not, because you’re about to get a crash course in what exactly this part is and what it does.
Back To Basics
The engine in your vehicle contains two rotating shafts. At the bottom, you’ll find the crankshaft. When your pistons fire (as a result of pressing down on the gas pedal) it causes the crankshaft to turn. That keeps the pistons in a fixed position relative to one another. Because of the way the engine works, only one piston can be at the very top center position at a time. The crankshaft ensures that the pistons will come to that center spot in a specific order at the right time.
Now, when the spark plug fires, it causes the air and gas mixture to burn, and subsequently forces the piston down. When the piston descends, it turns the crankshaft at the bottom. The turning of the crankshaft is what causes the flywheel and drivetrain to turn.
At the top of the engine is the camshaft. It regulates the timing of the opening and closing of the valves. That ensures that when the spark plug fires, there will be gas present. The exhaust is properly emptied so that the air and gas mixture can be reloaded and the entire sequence can occur again (over and over).
The most critical parts are the lobes. While the camshaft is spinning, the lobes are the parts that actually open and close the intake and exhaust valves. They do so in perfect synchronization with the pistons. Interestingly, engine performance at various speeds is directly affected by the shape of the lobes. Therefore, engineers place great emphasis on their production, depending on what type of performance capabilities the vehicle needs to have.
The most common types of camshafts are as follows:
- Single Overhead (SOHC)
- Double Overhead (DOHC)
- Pushrod
Without going into too much detail, here’s a brief overview of the main types:
Single Overhead
This type of camshaft has one cam per head on the engine. In other words, a straight 6 (inline 6 cylinder) engine would have one cam, while a V-6 would have two (one for each of the heads).
Double Overhead
You guessed it; double overhead cam engines have two for each head. So, using the same scenario as above, an inline-6 engine would have two cams, while a V-6 would have four.
Pushrod
The main difference between pushrod cam engines and singe/double cam engines is that pushrod engines have the camshaft actually located inside the engine block, rather than on the head.
If you believe you may be experiencing engine problems due to a malfunctioning camshaft, you should see a mechanic as soon as possible. Even though I describe a lot of these systems in these columns, repairing the components involved requires a trained hand. Unless you’re experienced, check with your mechanic. Most of the problems that involve this part are best left to a technician.
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February 17th, 2010 admin
Why Relying On Your Car’s Tire Pressure Monitor Is Unwise
All drivers realize that their safety depends, in part, on the condition of their car tires. It also depends on the pressure within them. If they’re underinflated, it’s possible to lose control of your vehicle, which can lead to disastrous results. A couple of years ago, the government noted the danger and got involved. They passed a law requiring all new cars, trucks, and SUVs that came off the assembly line to have tire pressure monitors (TPMs) installed.
So, that means there’s no longer a need to check the pressure in your wheels, right? Not quite. In this article, we’ll take a closer look at these systems. I’ll point out their limitations and why relying upon them can leave you and your passengers vulnerable to injury. I’ll also explain the two different types of TPMs available.
Are You Exposed To Danger?
It’s worth noting that a lot of these systems will only display a warning if your wheels are severely underinflated. At the time of writing, automakers are only required to program their tire pressure monitors to alert the driver if the level of underinflation reaches 25% or more. This is a problem. At that point (actually, well before it), your wheels can potentially blow out if you’re carrying enough weight in your car.
Unfortunately, most drivers depend upon their vehicles’ TPMs to warn them of a problem. As long as they don’t see the warning light, they assume they’re safe. If you’re driving with underinflated tires, it takes more time and room to bring your car to a complete stop If you need to brake quickly, you may find you’re unable to do so.
Different Types Of Systems
There are direct and indirect TPMs, though the former is far more expensive. The indirect systems rely on sensors that are a part of your car’s ABS. If one of your wheels is spinning at a quicker rate than the others, the indirect TPM determines that it needs air. As you can imagine, this type of monitoring is not an exact science.
By contrast, a direct tire pressure monitor relies on a gauge that is positioned on the wheel. When there is an underinflation problem, the gauge alerts the computer and the TPM warning light goes on. This type of monitoring is accurate within a few psi. The drawback is that a direct system is expensive.
Building A Good Habit
Relying solely upon your vehicle’s TPM (especially an indirect system) is a bad idea. Because the threshold at which the warning is triggered is set so high, relying on it exposes you and your passengers to unnecessary danger. Instead, get into the habit of periodically checking the air in your wheels. If they’re low, fill them. That way, you’ll help keep yourself, your passengers, and other motorists safe.
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January 27th, 2010 admin
Performing An Engine Leak Down Test
The performance of your car’s engine is dependent on the air and fuel that is drawn into each of the combustion chambers during operation. When air and fuel enter a chamber, the intake and exhaust valves close, sealing both inside. Within the chamber sits a piston. It rises and compresses the air-fuel mixture. A spark plug sits atop the chamber and ignites the compressed mix. The resulting explosion forces the piston down and ultimately is responsible for propelling your vehicle forward.
If the pressure within the combustion chamber declines due to leakage, misfires and similar problems can occur. That will hamper your engine’s performance. A leak down test measures pressure loss within the cylinders. A mechanic will often use this test to identify whether a leak exists as well as its root cause.
Below, you’ll learn how a leakdown is performed and some of the potential problems it can help to identify. If you have the proper gauge, you can do the test at home. Otherwise, an auto technician can do it for you.
How The Test Is Done
First, you’ll need to remove your spark plugs. You’ll then need to position each cylinder’s piston at top center of its chamber. Second, connect the coupling on your leakage gauge to the hole in which your spark plug usually rests. Third, fill the chamber with compressed air and take a reading on the leakage percentage.
It’s important to realize that there will always be some measure of leakage from each of the chambers. If the gauge shows less than 10%, your engine is fine. If the leakage percentage is between 10% and 20%, it’s still in good condition, but you’ll want to note any changes in its performance. If the gauge shows 30% or more, you have an engine problem.
Identifying Potential Problems
One of the advantages of a leakdown test over a compression test is that it’s easier to identify where the lost pressure is headed. This is important if fixing a leakage requires taking apart your engine.
For example, if you hear air leaking out of your car’s tailpipe, the problem is likely your exhaust valve. On the other hand, you might notice a whistling sound coming from your intake; that signals a leak in your intake valve. Hissing from your PCV valve suggests the piston rings are failing.
If you look at the top of your radiator reservoir (take the cap off) and see bubbles, it could mean a leakage problem with your head gasket.
As noted, a leakdown test is easy to perform at home. You’ll need a leak down gauge, a source for the air that you’ll send into each cylinder’s chamber, and a few tools (e.g. a socket to remove the spark plugs). Armed with those resources and a little free time, you can perform a leakdown to find the root cause of a pressure loss.
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