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16 answers

Well you have two questions. The first is what is the timing belt, and it is, as the name implies, a belt, not unlike a fan belt, but usually wide and flat with teeth on one side that serves to coordinate the opening and closing of valves with the rise and fall of the pistons inside the engine.

In a four stroke engine, which almost any car you are looking at will have, each piston goes through four distinct operations--two per revolution of the crankshaft.

First you have the intake stroke. Your intake valve opens to admit a fuel/air mix from the intake manifold, and the piston goes down turning the crank shaft half way round as it does, and the falling piston creates a suction in the cylinder that draws the fuel/air mix in.

Now the intake valve closes and the piston begins to rise back up compressing the fuel/air mix. This is called the compression stroke, and once again the crank shaft is turned half way round.

Then the spark plug fires and the resulting explosion drives the piston down again in what is called the power stroke. Once again the crank shaft is turned half way round.

Finally, the exhaust valve opens and as the piston rises again it pushes exhaust out past that valve into the exhaust manifold and, you huessed it, once again the crank shaft turns half way round.

Now, different manufacturers use different means of coordinating this ballet between valves and pistons, but among the most common is the timing belt. Essentially, there is a toothed wheel or gear on the end of the crank shaft to which the pistons are connected, and another toothed wheel on the end of the cam shaft in your cylinder head (and the cam shaft opens and closes the valves as it turns). By connecting the two with a belt, the cam turns at the right time to open and close each valve precisely when it is needed.

Now here it is important to mention that there are basically two designs of engines, one called interference engines and the other non-interference engines. On an interference engine it is terribly important that the belt does not break because the lowest point each valve can reach is low enough to come in contact with the highest point each piston can reach. As only the belt serves to coordinate their positions relative to one another, when the belt breaks in an interference engine pistons and valves can collide, often destroying the engine.

On the other hand, in a non-interference engine, the lowest point of travel the valves have is still above the highest point to which the pistons can reach. So if the belt breaks, the engine dies, and you drift off to the side of the road, but the engine is otherwise unharmed. All Hondas for example, are non-interference engines, while most Nissans are interference engines.

Now, as to how you can tell the condition of the timing belt? Well mileage is one way, and different manufacturers reccommend different service intervals for replacement, anywhere from 60,000 to 90,000 miles.

Another is a physical inspection by removing the timing belt cover and looking to see if the belt is frayed or cracked, or appears terribly dry and brittle.

As a general rule, unless there are reasons you do not wish to be stranded or inconvenienced, and if money is an object, I recommend running belts on non-interference engines to failure as the amount of time they actually will last can be 50,000 or more miles beyond what is specified. The only caveat I will add to that is that if you hear your valves making a little clatter, change the belt. It may mean it has become a little stretched and is not doing its job.

At the same time, I recommend changing belts on interference engines religiously on schedule as the consequences of failure are not simply that I will be calling a tow truck on my cell phone or hoofing it a bit, but severe engine damage.

As to whether it is a major consideration when choosing a used car, the price for replacement is anywhere between $150 and $400 depending on the car and the shop you ask to perform the job. If the belt is in need of replacement, or due, but you still want the car, you should use it as a negotiating tool to try and get the price down a bit to take into account the pending repair. But the same might be said, for example, if the car has not had its 60,000 mile service and now has 65,000 miles on it, or if the tires have relatively low tread, or any number of other things. The mechanical condition of the car you are looking at is always a factor in the negotiated price.

2006-07-28 16:39:51 · answer #1 · answered by anonymourati 5 · 2 0

The timing belt is what turns the camshafts. It connects the camshafts to the crankshaft so the valves can open at the correct time.

There is a scheduled maintenance interval for all cars equipped with timing belts. The dealer of this particular make can tell you what that is (typically now 90,000 miles). So if the car is below the scheduled maintenance interval you have no worry. If it is above and there is no sticker (most dealers will install a sticker to notify when the belt was replaced last) replace it when you buy it. If you are buying it from a dealer ask them to replace it before you buy the car (insist they use the dealer for repair that way you will get the correct quality belt and a qualified technician to complete the repairs) which shouldn't be a problem.

Hope I was helpful and didn't just babble on...

2006-07-28 22:46:20 · answer #2 · answered by ubet426 4 · 0 0

Often you can't see the timing belt/chain, they are under tightly sealed covers on the front of the engine behind the fan usually. They are the mechanism that keeps the engine cylinders firing in the right order (basic). When the timing belt breaks you are on foot, period! And they can be extremely expensive to replace on some models. Do your research online at edmunds.com or some other car related web sights. There are some models that you should NOT buy if the timing belt has not been changed. Be careful.

2006-07-28 22:48:38 · answer #3 · answered by AK 6 · 0 0

Timing belt is what connects the crankshaft of the engine to the valve train, so the valve will open and close in appropriate timing.
The timing belt is made from rubber-like material and it last only for a limited time. If the car has more than 70,000 miles you should at least have it checked by a mechanic or replace for your peace of mind. Don't trust dealers if they tell you it was replaced unless there is a trustable proof like a service receipt. I've seen many times they say it was replaced when it wasn't

2006-07-28 22:55:42 · answer #4 · answered by svthech 4 · 0 0

You don't actually. If the car runs chances are the Timing belt is okay at that time.
Along with the Timing belt, the Gear running the Timing belt could go wrong.

Without actually disassembling the cover, and examining the belt and gear, you will never know if there is a problem even then you cannot promise they will last. Best take your chances if the milage is acceptable, or when you buy the vehicle, replace them yourself.

2006-07-28 22:49:29 · answer #5 · answered by dogwarrior2001 4 · 0 0

It's also worth mentioning that some cars do not have timing belts. It's possible to use gears or chains instead. These are far less likely to break, and usually show up on older engines.

2006-07-29 08:39:26 · answer #6 · answered by Mad Scientist Matt 5 · 0 0

the timing belt times the crankshaft with the camshaft, it is considered a maintenance item. depending on the make and model of the car it could be expensive. what i would do is have a mechanic give you an estimate on how much it would be to replace it and that would give you a better idea of how much the car will really cost you.

2006-07-28 22:45:32 · answer #7 · answered by b_racer_88 2 · 0 0

Look at the repair records! This can be VERY important for some models;as the Whole motor Stops if it goes AND can have real bad consequences as far as the motor goes after that.

Some cars are a given at about 30k miles, just like you'd change oild, rotate tires, etc.

Be careful!!

2006-07-28 22:45:22 · answer #8 · answered by Anonymous · 0 0

Tell the dealer or the person you are buying the car that you would like a free DMV report and carfax report which will tell you the complete history of the cars maintenance. IF the seller says no then pass regardless of the deal he/she is offering.

2006-07-28 22:43:28 · answer #9 · answered by bebe1028 2 · 0 0

The timing belt is used to drive the camshaft in over head cam engines (o.h.c.) The only way to check that it is serviceable is to inspect it. The only way to be sure that it is good enough is to replace it. Under normal running conditions service times are replacement at approx. 100,000 Km, (60,000, miles) .

2006-07-28 23:00:28 · answer #10 · answered by ALLAN J 2 · 0 0

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