What is the difference between timing belt and timing chain?

What are timing belts and timing chains and how do they differ from each other? Well, the simple answer is one belt and the other chain. Of course, this is not a very useful answer. You also want to know what…

What are timing belts and timing chains and how do they differ from each other? Well, the simple answer is one belt and the other chain. Of course, this is not a very useful answer. You also want to know exactly what they do, so let's start with a little talk about engine timing, which is the reason your car needs a belt or chain.

Fundamentals of mechanical engine timing

Most cars today have four-stroke gasoline engines. This is because the combustion process has an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. During a four-stroke cycle, the camshaft rotates once and the crankshaft rotates twice. The relationship between the rotation of the camshaft and the crankshaft is called "mechanical timing". This is what controls the movement of the pistons and valves inside your engine's cylinders. The valves need to open at the exact time along with the pistons, and if they don't, the engine won't run properly, if at all.

Timing belts

Around the mid-1960s, Pontiac developed an inline-six engine that was the first American-built car to feature a rubber timing belt. Previously, almost every four-stroke engine was equipped with a timing chain. The advantage of the belt is that it is very quiet. They are also durable, but wear out. Most car manufacturers recommend timing belt replacement every 60,000-100,000 miles. Now that you know the function of the timing belt, we probably don't need to tell you that there will never be a good result if you end up breaking the timing belt.

The timing belt runs through a series of pulleys on which belt tensioners are mounted. As you can guess from the name, the function of the belt tensioner is to maintain proper belt tension at all times. They usually wear out at the same time as the belt and are changed along with the belt replacement. Most manufacturers and mechanics also recommend replacing the water pump. This is because the water pump is usually the same age and usually wears out around the same time.

Timing chains

Timing chains serve the same purpose as a belt, but usually last a little longer. Some manufacturers offer to replace it at regular intervals, others claim that it will last as long as the car itself.

A timing chain is similar to a bicycle chain and, as you might expect, noisier than a belt. Another problem with timing chains is that if they break, they usually do much more damage than a broken belt. It's not that we're saying that a broken timing belt won't cause you problems - it definitely will. But with a broken belt, one could just fix the heads. A broken chain is more likely to cause damage, making a complete engine rebuild cheaper than the repairs you'll need.

The timing chain also has tensioners that hold it in place, but unlike belt tensioners, timing chain tensioners are controlled by engine oil pressure. So if the oil pressure gets too low for any reason, the tensioners will fail, the timing will shift and the chain will most likely fail in spectacular fashion. Chains have the advantage that they have nothing to do with the water pump, so you usually don't need to replace the pump at the same time you change the chain.

Interference engines

No discussion of timing belts and timing chains would be complete without a few words about interference engines. In an interference engine, the valves and pistons occupy the same place in the cylinder, but not at the same time. This is a very efficient type of engine, but if you're careless with its maintenance, you can get in trouble. If your timing belt breaks, the valves and pistons can end up in the cylinder at the same time. We probably don't need to tell you that that would be really bad. On a non-interference engine, the belt could break and cause no internal damage because the pistons and valves are never in the same place.

So, how do you know if your car has a cluttered engine or a non-cluttered engine? You will most likely need to contact your dealer or mechanic.

What happens when the timing belt or chain is damaged?

With proper maintenance, it is unlikely that you will have problems with the timing belt or timing chain. But when this happens, as we have already said, there is no good result. So what exactly is happening?

The timing belt usually breaks when you start or stop the engine. This is simply because it is at this time that the belt tension is at its maximum. If you have a clutter-free engine, you can usually get away with just installing a timing belt kit. If it's an interference motor, there will almost certainly be some damage. How much will depend on the engine speed at the time the belt is thrown. If this happens on shutdown or startup, you will likely end up with bent valves and/or broken valve guides. However, if it starts running at high RPM, the valves will most likely break, bounce around the cylinders, bend the connecting rods and destroy the piston. Then, as the piston breaks, the connecting rods start punching holes in the oil pan and cylinder block, eventually cutting the engine apart. If you think this sounds like a repair is impossible, you are right.

Now about the timing chain. If the chain breaks at low speed, it may simply slip off and do no harm. You simply install the timing chain kit and you're done. If it breaks or breaks off at high RPM, it will destroy almost everything it comes into contact with. Repair may be possible, but it will be costly.

Correct service

Maintenance is vital. If your vehicle manufacturer recommends that you change your belt or chain regularly, do so. Letting it go is very risky and, depending on the age of your car, it could result in repairs costing far more than the actual value of the car. If you have bought a used car and are not sure if the timing components have ever been checked, have a mechanic check the car.