What do these two things have to do with each other? At first glance – it might seem like there’s absolutely nothing at all.
But if you understand just what goes on inside a motorcycle engine, you’ll realize that the cam chain is what makes valve timing possible.
In this blog post, you’ll discover:
- What a cam chain is, and where you can find it in the engine
- Why valve timing is vital – and what happens if it’s wrong
- Some common cam chain FAQs – including whether cam chains need to be replaced
What’s a Cam Chain and Why Does Your Engine Have One?
Before we get started properly, I’d like to point out that a cam chain is NOT the same thing as a drive chain – the cam chain sits fully enclosed inside the motorcycle engine while the drive chain is out in the open.
Anyway, the cam chain is a chain that wraps around the pulley of the camshaft at the top of the engine and the pulley of the crankshaft at the bottom of the engine.
And this chain is absolutely vital for a functioning internal combustion engine.
To understand why this is so vital, we need to talk about valve timing.
What’s Valve Timing, And Why Is It So Vital?
Inside the engine, there are these small, thin metal pieces and a set of metal springs called “engine valves,” or just “valves” for short.
In terms of design, the valves are not complicated – just a metal stem with a round shape at the bottom. But it may surprise you that despite their simplistic design, they perform a vital role in any internal combustion engine.
And that role is to control the flow of fuel and exhaust gasses that go into and out of your engine.
Without valves, fuel can’t enter the combustion chamber, and the exhaust gasses can’t enter the exhaust system (not that there would be any to begin with, especially since there’s no fuel to ignite).
It doesn’t matter if you’ve got a 50cc Peugeot Speedfight 4 or a 900 cc Kawasaki Vulcan – at the bare minimum, every motorcycle engine has at least two valves – one for the intake and one for the exhaust.
I could go into more detail on the topic of valves and about terms like “valve bounce” and “valve float,” but I won’t.
After all, this post is all about valve timing, so let’s stick to that. To summarize it in just one sentence, valve timing is when the intake and exhaust valves open and close in relation to the piston’s position.
If they’re not, expect engine troubles. Serious engine trouble.
What happens if the valve timing is incorrect?
As I just showed you, the intake and the exhaust valves must open at a certain point to avoid the engine piston slamming into them.
Keep in mind – valves are thin pieces of metal. The engine piston, however, is much larger (not to mention stronger).
You don’t have to be familiar with the law of gross tonnage to know that if a larger piece of metal slams into a smaller piece of metal, that smaller piece of metal will be damaged severely.
In this context, the “larger pieces of metal” is the engine piston, and the “smaller piece of metal” is the valve.
And if the piston damages the valve, it will bend (see the image below for the result), which in turn, means that the valve will not close properly.
Usually, this causes:
- Reduced engine performance
- Knocking noises
- Misfiring
Original image provided by Andrew Fogg, CC BY 2.0, via Wikimedia Commons
OK – so where does the cam chain come in?
Well, it’s what makes valve timing possible – it wraps around the camshaft pulley at the top of the engine and the crankshaft pulley at the bottom.
Although the camshaft does most of the hard work to open and close the valves, without the cam chain, none of the engine valves would open and close when they need to.
As long as the chain is wrapped around both of these pulleys and the timing marks on the camshaft are aligned, the valve timing will be correct.
Cam Chain and Valve Timing FAQs
Do you have to change a cam chain?
If you’re familiar with cars, you’ll know all about cam belts (AKA “timing belts”) – more specifically, the dreaded belt replacement you have to do every 100,000 kilometers or 60,000 miles.
In that case, you’ll be happy to hear that a cam chain doesn’t need to be changed as regularly – generally, it lasts as long as the engine itself.
The main thing to keep in mind is that unless the chain is in rough condition, there’s no need for you to replace it.
Cam chain vs. timing chain – what’s the difference?
Not much – apart from the choice of words, there’s no difference. They’re pretty much the same.
What are some common loose cam chain symptoms?
Do you hear a rattling sound coming from your motorcycle’s engine? If you do, that’s the most obvious sign that you have a loose chain.
How is valve timing set?
For four-stroke engines, the camshaft controls the timing of when the valves open and close.
As for two-stroke engines, many have their valve timing set through port timing, although some use the same camshaft approach as four-stroke engines.
If you’d like to read more about port timing, here’s an article on mecholic.com that goes into more detail.
