What is Valve Clearance that is Commonly Heard in Engine Overhaul? What are the Symptoms and What are the Effects?

Have you ever heard of a heavily tuned engine that requires severe valve clearance adjustment? Even if you have OEM engine that is not highly tuned, have you ever been told by an engine expert that the valve clearance may be too large after a long period of use? I'm sure you have!

But! Even if you're told that, you don't fully understand valve clearance, and what you should do even if the clearance is wider? But don't worry! The majority of people in the world can't adjust the valve clearance, and it's not even clear if the valve clearance is really wide in the first place.

WebiQ is here to bring you a little happiness and motorcycle knowledge. Instead of asking how to adjust valve clearance, what is valve clearance? I will explain whether it widens or narrows after many years of riding, the reason why the clearance changes, and what symptoms it can cause.

You can do the adjustments yourself, and that's fun, but if you're not confident in your maintenance skills, just ask the motorcycle shop to do it for you!

What are the symptoms of needing to adjust valve clearance?

Let's talk about the difficult mechanics later. What are the symptoms first?

The first thing you will notice when you need to adjust the valve clearance is a change in the engine noise. However, this does not mean that the exhaust sound will change, but the noise coming from the engine itself will change.

Specifically, when starting the engine, you will hear a "tick-tock ......" sound coming from the cylinder head area.

This sound gets faster in proportion to the engine speed, so if you rev the engine to a higher rpm, it becomes a continuous sound and difficult to judge. Therefore, the best time to hear it is when the engine is idling. If you hear a ticking sound that is different from what you heard before, be careful!

If you are used to it, you can tell just by listening to the engine noise while idling. This sound has a name: tappet noise.

It's usually easier to detect if you listen carefully to the engine.

If the symptoms go unnoticed ......

If you have a noisy race exhaust system, are indifferent to the engine noise while idling, or are so absorbed in music or talking that you don't have the habit of paying attention to the sound emitted from the motorcycle body on a regular basis, you may not notice any change in the tappet sound while idling.

The symptom that even these people notice is the power down, which everyone hates. In the terminal stage, the power down is quite obvious, and everyone will feel that something is wrong. You can feel it. As you can see, at first it's just a sound, but in the end it's a power down.

There are other engine problems that make a similar sound.

There are so many problems other than valve clearance that make a similar sound that are very likely to develop into serious engine problems. The pistons are worn out and tilted in the cylinder, some foreign object is caught in the piston, a gear is missing, etc. All of these can lead to fatal problems, so don't just assume it's valve clearance just because you hear a ticking sound! It is better not to assume that the ticking sound is valve clearance.

Is the noise really caused by the valve clearance? It is important to identify the source of the noise. There are special tools on the market to identify the source of the noise, so don't underestimate them.

It is better not to assume that the sound that is a sign of serious trouble is the sound of valve clearance, because it will be a serious problem if you mistake it for the sound of valve clearance.

What is the need for adjustment and what are the effects? What happens if it's left unattended?

If you hear a ticking sound coming from the cylinder head, you can almost certainly assume that it is a tappet sound caused by a valve clearance problem.

However, the tappet sound is not something that occurs all of a sudden; it is something that you notice one day when the sound gradually gets louder and louder. It's a good idea to have a good idea of what you're doing. What does that mean? It doesn't happen suddenly, and it doesn't get worse suddenly.
I did it.

It's not like the engine suddenly stops working.

In this way, the valve clearance does not suddenly deteriorate and suddenly blow the engine. However, you should not be relieved just because it works for the time being.
Once you notice the ticking noise, you will notice it every time you ride, and if the symptoms are advanced, you will also notice a definite power reduction, so it's best to adjust it properly when you notice it. Even if you leave it alone. It will never recover naturally.

On the other hand, if you leave it alone and think it's okay if it doesn't break down suddenly, the symptoms will get worse and worse. In this case, the speed of deterioration is much faster than you think.

For example, let's say you start to hear a tappet sound at 100,000 km, but it is only slightly audible and not too loud. If you use it gently, it will be fine for about 150,000km. Unfortunately, this is not the case. Once the tappet noise starts to appear, the symptoms worsen at an accelerated rate. My own feeling is that once the sound starts, it gets worse 100 times faster than before.

I imagine that once a gap is created, the impact will be greater for the gap created, or the valve will jump for the gap, and it will get worse all at once. I imagine so. It may be similar to the way a chain sprocket is torn apart at an accelerated rate when it is slightly worn.

The gap creates an impact and dents, which creates more gaps, and the gaps keep getting wider?

Adjusting the valve clearance is a process of restoring the engine condition after a long period of driving, so readjusting it correctly will reduce engine noise and increase power. If you notice a ticking noise from the engine, don't leave it unattended, readjust it as soon as possible.

What is valve clearance and where is the gap?

The "clearance" of the "valve" is somewhere inside the engine, so you know where it is. However, it is rare to find someone who is familiar with the internal structure of an engine, or who can completely reproduce the movement of each part in one' s mind just by looking at a cross-sectional drawing or a cutaway model.

So, to explain it very briefly, it is the gap between the tip of the valve and the part that pushes the tip of the valve down. In other words, valve clearance adjustment is to adjust the size of the gap at the valve tip! By the way, valve clearance is also called tappet clearance, and both mean the same thing.

It's not always just about widening (greater clearance).

So far, I've been talking about the fact that the bulb clearance is supposed to widen and increase, because each part of the valve will decrease over the years. The majority of what is written about valve clearance adjustment in the world is the same: the clearance widens and grows, so you have to adjust it to reduce or close it to the correct value.

Basically, this is correct, and the tappet sound (i.e., striking sound) becomes louder because the clearance widens. However, there are exceptions to this rule, and in some cases (very rare), the valve clearance may become narrower.

One of the reasons for this is that the valve seat, which is the part that the valve umbrella contacts, is reduced.

This is a part that is supposed to wear out since it is the part that the valve that is moving at high speed collides with, but when the speed of wear exceeds the momentum of the valve tip contact, the valve clearance decreases. In the worst case scenario, the valve clearance will be 0 mm (no gap), and the valve may not be able to close due to thermal expansion of the engine. If the valves are not able to close completely, the gas in the combustion chamber will not be able to be sealed, which will directly lead to power loss.

A typical example is, where there is no tappet sound (ticking sound) but the intake passage is black with carbon buildup. It seems to be more likely to occur when the air cleaner is removed and the engine is funneled, which can easily suck in sand particles. If you have any of these symptoms in mind, consult a motorcycle shop immediately!

In addition, although it is rare, it is possible that the previous owner of a used motorcycle failed to adjust the valve clearance, and the clearance is not only 0 mm, but even negative. Since there is no clearance, there is no ticking sound at all, but in this case, the valves are always slightly open, which makes the engine condition very bad. This is especially true when starting and idling, but if you judge this to be a carburetor setting error, you will be stuck in a quagmire that will never be solved.

 

Could it be that the sand that is sucked in acts as an abrasive and accelerates the reduction of the valve seats?

The engine needs to be opened to make adjustments.

In order to adjust the valve clearance, it is always necessary to open a part of the engine. Since the valves are internal parts of the engine, there is no way to get to them in order to adjust them.

Most people would be hesitant to open up the engine, even partially. So, there is no need to force yourself to adjust it. The best thing to do is to ask a motorcycle shop for help.

However, it is a given that the valve clearance of an engine will change as it is used.
This is why all engines are designed to have easy-to-adjust valve clearances.

The fact that they are designed to be easy to adjust also means that it is easy to try to adjust them yourself. If you are interested, we recommend that you try to adjust it by yourself. Of course, it's not easy when you're doing it for the first time, but that's part of the fun of biking!

On rocker arm type engines with screw-type tappet adjustment, it is often easy to adjust by simply opening the cover.

It's not that much less with the latest model.

This valve clearance adjustment is not something that is normally done very often. For some engines with special modifications, but for normal engines, the first adjustment is done after a few tens of thousands of kilometers. Depending on the type of motorcycle, there may be no problem even if the engine is not adjusted for 100,000km. In particular, the materials and design of modern motorcycles have improved so much that they may never need to be adjusted from the time they are purchased to the time they are scrapped.

On the other hand, older motorcycles, especially those with air-cooled engines whose main selling point was high performance, often have crazy clearance problems. If you have a small displacement engine and you are always using the engine performance to the limit, the period for valve clearance adjustment tends to be short.

Since the clearance changes slowly and gradually, it is important to pay attention to the engine sound on a daily basis, and when you hear a ticking sound, it is time to adjust.

Surprisingly easy, but difficult to master

To sum up what I've been telling you so far.

However, this is really just the basics, and there are plenty of exceptions.

There are many exceptions to this rule. For example, some air-cooled high-tuned engines have a very large valve clearance from the beginning in anticipation of the thermal expansion of the valves at high rpm and high load. These engines make a loud tappet sound immediately after starting, but when the engine is performing at high rpm and high load, the clearance is optimal.

On the other hand, if the thermal expansion of the cylinder head itself is greater than that of the valves, the valve clearance may be extremely narrow when the engine is cold.

For stock engines, which are not tuned, the valve clearance is always specified by the manufacturer, but this is the optimum clearance derived from the results of extensive testing. However, this is the optimum clearance derived from extensive testing. There is nothing good to be said for a wider or narrower clearance, so the basic rule is to adjust the valve clearance as specified in the manual.

However, when readjusting, arrangements may be made in anticipation of the fact that various parts are already worn out. It would be optimal to replace all the relevant parts with new ones to achieve the manufacturer's specified value, but if you reuse parts that are still available due to budget constraints, the manufacturer's specified value may no longer be optimal.

Adjusting the valve clearance after driving a certain distance is a normal thing, so it is designed to be easy to do, and the adjustment itself is surprisingly easy to do. If possible, we recommend that you try to adjust it yourself. However, it is important to know that the difficulty level of even the simplest adjustment work can increase dramatically if you try to master it, which may change the way you look at a motorcycle shop!

Skilled motorcycle shops have their own unique know-how.