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What is a Timing Chain?
In any internal combustion engine (ICE), the intake and exhaust valves need to open and close at the right time. This is controlled mechanically, using a camshaft.
A camshaft is made of several key components. The main ones you need to know about are:
- The cam lobes
- The cam journals
- The sprocket
The cam lobes are vaguely raindrop-shaped parts attached to the camshaft. As these rotate, they force valves to open and close. How open the valve is depends on the shape of these lobes. These parts are the whole point of the camshaft. It enables the valves in each cylinder to open at precisely the right time.
Camshaft journals hold the camshaft in place. They are placed inside a bearing and thus can fully rotate with the shaft.
On the end of the camshaft is the cam sprocket. This is a sort of gear, fixed to the shaft, that spins at the same rate as it. The camshaft sprocket is a vital part of the timing chain system, as we shall see now.
So, the timing chain.
The timing chain is attached to the cam sprocket. It’s also attached to the crankshaft sprocket underneath. These two sprockets, or gears, are precisely manufactured so that, when the crankshaft (and its sprocket) spins, the camshaft spins at exactly half the speed of the crank. The timing chain links the two and ensures they always turn at the same rates with each other.
This means that the valves will open at precisely the right time for the 4-stroke process of most internal combustion engines to occur.
What is a Timing Belt?
In some cars, a timing belt is used instead of a timing chain.
You’ll probably find this to be the case on cars that aren’t old yet, but you wouldn’t describe as modern either.
Timing belts were the preferred choice for a while because they run much more quietly than timing chains. They’re also cheaper to produce than timing chains, in terms of raw materials. Manufacturers often need to save as much money as possible in the design of their vehicles.
The main disadvantage of a timing belt (as opposed to a chain) is that they deteriorate quickly. Because of this, there’s a higher risk of damage being caused to the engine unexpectedly.
In recent years, manufacturers have started to return to using timing chains again.
What Will Happen if the Timing Chain Goes?
We won’t sugar coat this – nothing good. In fact, definitely bad things. Really bad things.
If the timing chain breaks or slips, for whatever reason, it will result in the camshaft either opening the valves at the wrong time or not opening them at all. Because the valves won’t open, the exhaust gases can’t leave the engine, and the intake valve can’t open.
In some engines, the air and fuel are mixed before entering the cylinder through the valve. In some engines (direct injection), fuel is injected straight into the cylinder and mixed with air before the piston rises again.
No matter what the engine type is, if the camshaft isn’t turning, no oxygen will be getting into the engine. In direct injection engines, though, fuel will still be going in, the sparks will still be firing, and explosions will still be happening.
This is all monumentally bad for your engine. It’s basically one of the worst things that could happen.
Due to the excess forces put on everything, you can expect to see:
- Bent or completely broken valves
- Damaged con rods
- Damaged piston rings
- Loss of compression / damaged cylinder walls
- Damaged cylinder head and block
- Damaged exhaust manifold and pipe (if metal gets through)
- Damaged turbo (if metal gets through)
- Damaged intake manifold
- Essentially, damage to basically anything within the engine
Unless your car has a non-interference engine (where the valves don’t travel into the area that the piston goes into), this will cause an untold amount of destruction to your motor.
Is the car dead, then?
In cold-hard brutal reality, almost certainly. That is unless you want to pay out a bomb for a huge rebuild. You’re more likely to need an engine replacement than a rebuild in this situation.
How Can I Tell It Might Need Fixing?
Needless to say, having the timing chain break on you isn’t something you want to happen. It’s something you want to avoid at all costs.
Here are a few of the signs that you can watch out for to make sure you catch this problem as early as possible. Getting the timing chain changed for a new one before it goes could save you a huge amount of dollars.
- The check engine light is on – When the check engine light is on, it’s always going to be for a reason. As soon as the light comes on, it needs investigation. This may be the only indication you get of your timing chain being about to go. If the light stays on after turning your car off and on a couple of times, take it straight to your local garage. They will use a code reader to diagnose what’s wrong and, if it turns out to be the timing chain, they can help you to get it fixed.
- The engine is misfiring – The chain could stretch and jump a tooth on either sprocket (either the camshaft or crankshaft). If this happens, the valve timing will be slightly out. If this is the case, air will be entering and leaving the cylinders at slightly the wrong time, leading to the explosions being less powerful than usual. As a result, you will have a loss of power and see and feel the engine misfiring.
- There are shavings of metal in the engine oil – When your car gets serviced, the mechanic will empty the engine oil into an oil pan before topping the car up with a fresh load. There may be clear evidence of metal shavings in this oil. These metal shavings indicate something metallic is deteriorating in the engine, which could be your timing chain (or other things, too). If you’re changing the oil yourself, it may be best to ring a mechanic and see what they think the best course of action should be.
- Strange noises while the engine is idling or running quietly – If you can hear a sort of rattling, this may be an indication of the timing chain being about to go. Your timing chain could cause this sound as it loosens.
Fixing Your Timing Chain
It’s possible to fix your timing chain by yourself, but you must be very precise and often need some specialist equipment. If you aren’t sure about what you’re doing, we would recommend leaving it up to your local mechanic.
With all problems, it’s better to stop them from happening in the first place than have to fix them when they inevitably occur. Look after your car, and it will look after you.
The timing chain is a small, overlooked piece of the engine, but it’s critical.
We hope this article has helped you know what to look out for!