The main difference between a timing chain and timing belt is that the chain is made from metal and resembles a bicycle chain. A timing belt is made from heavy duty rubber and has teeth along its inner edge to hold it in place.
A timing chain does the same job as a timing belt; it keeps the timing of the engine pistons in sync with the movement of the air valves by joining the rotation of the crankshaft and camshaft.
The one big difference between the two, is that the timing belt must be changed at regular intervals as it can wear and break, possibly causing major engine damage.
In this article, I'll explain the function of both the chain and the belt and the pros and cons of each
What is the difference between a timing chain and timing belt?
Timing chains and timing belts may perform the same job, but they are very different in how they operate and how long they last:
1. Made from metal
1. Made from strong rubber
2 Is fitted inside the engine
2 Fitted to the outside of the engine
3 Needs oil for lubrication and to help tension it
3 Must run dry and uses automatic tensioners to keep it in place
4 Can last the lifetime of the engine
4 Must be changed at intervals
5 Difficult to replace
5 Designed to be easier to replace
6 Can be noisy in operation
6 Much quieter than a chain
Overall, the timing chain requires much less maintenance, but if it does, it is much more difficult to carry out.
A worn chain can become noisy and may rattle, especially when the engine is cold. However, when compared to a timing belt, it is much less susceptible to breakage.
What happens when a timing belt or timing chain breaks?
Timing belts are designed to be changed at regular intervals, traditionally around 60,000 miles. Newer vehicles have timing belts that can last up to 150,000 miles, but even so, it is still advisable to change them regularly.
This is because of the potential damage that can be done if a worn belt were to break. Most timing belt breakages will occur at engine start up or at shutdown, as this is when the most pressure is on the belt.
A snapped timing belt can cause major engine damage, as valves and pistons can hit each other and possibly bend or shatter. Some engines are designed so this cannot happen, these are called non-interference engines. These will usually just require a new timing belt and tensioner to get them going again.
A broken timing chain is not good news either, but it is less common. Timing chains are incredibly strong and are more liable to stretch than to break. The weak point with timing chains is not the chain itself, but the tensioner that keeps the chain in place. These tensioners have a limited life span, and can be greatly affected by inadequate servicing or the use of inferior engine oil.
A broken timing chain is worse than a broken timing belt. A timing chain that breaks at high speed will ruin an engine, and may even shatter the oil sump. I've never seen a broken timing chain, but I have seen a chain that has 'slipped' because of a broken chain tensioner. This can still cause a lot of damage, and it will often be easier to replace the engine.
What is Engine Timing?
The timing of a combustion engine refers to the rotation of the crankshaft and camshaft, and how this affects the movement of the pistons and valves in relation to one another.
Most modern car engines employ a four stroke system:
For every turn of the camshaft, the crankshaft will rotate twice. It's vital that the timing of the rotation is kept in synchronisation so that the pistons do not come in contact with the valves as they open and close. This type of engine is called an interference engine, and is very common in cars today.
It is the job of the timing belt or timing chain to keep the crankshaft and camshaft in time with one another.
Replacing a Timing chain vs replacing a timing belt
Timing Belt Replacement
Replacing a timing belt is a very common service procedure. Depending on the driving conditions the car has been exposed to, the timing belt should be replaced between 60,000-150,000 miles. This interval is set by the manufacturer and depends on the engine type, and the type of belt used.
The cost of replacing a timing belt depends on the amount of work needed to get to the belt. Prices usually start around $400 and could be double that if there is a lot of labor involved. I usually try use Gates timing belts, here's an example of one of the kits they supply:
When replacing a timing belt it's also a good idea to replace the tensioners and water pump too. This is because if any of these parts fail after replacing the belt, then you will need to strip everything down again to replace them. There's also a chance that a jammed water pump will snap the timing belt.
Timing Chain Replacement
Changing a timing chain is a lot more work, and often involves removing the entire engine from the vehicle.
A timing chain can last for the life of the engine or in real world terms 300,000 miles or more. The lifespan of the timing chain depends on how well the engine is cared for. Regular oil changes using a good quality oil are the key to a long lasting timing chain.
If the timing chain needs attention, then most of the time, it's the timing chain guides, tensioners and silencers that need replacing. The timing chain itself can also stretch slightly, which can play havoc with the timing of the engine.