Hi, (wasn't sure where to post this, so here it is)


*THIS BASIC OUTLINE WORKS FOR ANY UNDERBONE MOTORCYCLE INCLUDING SUZUKIS, YAMAHAS, KAWASAKIS AND ALSO MANY OTHER BIKES AS WELL, 250-400s included.



Many many people (2 or 3) have either asked me if I know someone who will adjust the valves on their bikes, or if they can attempt it themselves. I've shown several people in person how the process is done, but ultimately I've found that not many understand what they are actually doing and why it is important to adjust valves.

So this is not only going to be a step by step guide, but also a visual explanation of what valve clearance is and why it is important as well.





***Before we start FAQ***

Q: How often should I check my valves?

A: I recommend around 15,000 km intervals, but have seen bikes with far more km’s that have needed no adjustment, mine included. Often times I find that when I check the clearance, no adjustment is needed.


Q: My valves are noisy I think, will running them noisy ruin them?

A: Often times no, but our definition of noisy is very subjective. Often times people complain of valve noise and don’t realize that the valves are just fine and not “noisy” at all. The thing you have to be most cautious of is not noise, but silence. If the valves are quiet and haven’t been adjusted in a long time, then you should at least have the valves inspected and if necessary, clearanced.


Q: Why do quiet valves mean trouble?

A: You will see later on in the guide, but in short, it is because quiet valves are valves that are (potentially) not closing properly, and valves that do not close properly are subject to being burned and destroyed.


Q: What happens when my valve gets burned?

A: Your bike will stop running immediately (if it’s a single cylinder) or will run very poorly if it’s a multi cylinder.


Q: Will adjustment correct the problem after it’s burned?


A: No. The only way to “correct” the problem is to replace the valves, which means overhauling the top of the engine at minimum. Adjustment only prevents burning in this sense.


Q: How hard is it to do by myself?

A: Hard is subjective term, so that’s why I have the guide so you can see what is necessary and judge for yourself if you can do it.





Step 1: Prepare with tools and equipment

THIS IS A STEP BY STEP GUIDE ON HONDAS ONLY. THE SAME BASIC PRINCIPLES APPLY TO ANY BIKE WITH ADJUSTABLE TAPPETS THOUGH.

On Honda Super Cubs, Waves and misc Honda based bikes, you generally need...

8mm “curved” spanner
9mm “curved” spanner (not sure what they’re called, only that they’re not straight)
8mm socket
10mm socket
14mm socket wrench (if electric start)
16mm socket (if you wish to remove the spark plug)
17mm spanner/socket
Needle nose pliers
Some paper towels or rags
Feeler gauges


For the fast “hands on approach”

Spark plug socket (16mm)
Drinking straw (to determine piston position and TDC)
9mm spanner (retaining nut)
Needle nose pliers (holding adjuster)
17mm socket (remove valve cover)


***Cylinder head removed for ease of explanation***


***VERY IMPORTANT, engine must be “cold”. I’ve found that 4 hours is sufficient for most motors to cool down, but to be safe, I’d leave it overnight if possible. If you want to rush a cool down job, you can pull your cylinder head off and put it in the icebox for 15 minutes.


Step 1 (not necessary if you removed the cylinder head): Remove the cam chain cover. 10mm bolt on other side of motor.

Step 2: Rotate the camshaft to TDC (top dead center) or on a horizontal engine I suppose it’s call MSP (Most Sideways Position)?



On Hondas (although this is actually a Sangyang 100), the TDC mark is at the 270 degree mark on the cog wheel. Verify TDC for your particular bike to be safe though.





**On a Honda, to illustrate how close you need to be, here is one tooth advanced and retarded for example. Note the position of the right most bolt on the cog wheel and how it corresponds to the mark on the two positioning posts further to the right.






Now remove both valve covers.





This is what you should see. Hello valve.

At this point, if you’re familiar with valve tappet adjustments in general, you can get away with this super fast but potentially catastrophic way of doing things. To ensure that the average layman doesn’t get confused, I’ll use mechanic “jargon”. If you don’t understand the following, don’t attempt it this way.

**THE FAST WAY FOR HONDAS**

Set the clearance to zero. Rotate tappet 50-60 degrees ACL and secure the retaining nut. Done.

*********

If you don’t get that, then refer to the next walkthrough.

Undo the nut and then with the needle nose pliers (or your fingers if you can manage), loosen the adjuster (square head thing) a few turns to ensure free movement of the rocker arm.



Now with your feeler gauge (varies between models, this Sangyang is .0015” intake .0020” exhaust) insert the appropriate feeler gauge between the tappet face and the valve head.

**I like to bend my feeler gauge like so to make things easier**




EXPLANATION, what is .0015”, .002” etc? This refers to a measurement of .0015 inches or .04 mm. Feeler gauges will have the measurement stamped on them. Be careful not to confuse MM with INCHES. I learned on metrics, but working on American cars often, I had to learn to differentiate between that and inches and often if I wasn’t careful, would default to metric. \

EXPLANATION, when referring to intake and exhaust, what does that mean? Intake means the intake valve or the valve the opens to allow air and petrol mixture into the engine. Exhaust means the valve that opens to allow the exhaust to escape. A general rule of thumb is that the exhaust valve is always SMALLER than the intake. I’ve personally never seen the contrary.


***If it’s difficult to figure where to insert the feeler gauge, then here is a better view of things.





Here is where the gap is (greatly exaggerated). On top is the adjuster.




Here is where the feeler gauge is supposed to go.










Tighten the adjuster (square peg) clockwise until it contacts the feeler gauge. DON’T SMASH IT DOWN THOUGH, just loosely finger tight is good. You need to be able to move the feeler gauge still to get it out. Just a little bit of drag is optimum (observe how feeler gauge is movable in pic).




Now, while holding the square peg with needle nose pliers, tighten the retaining nut down make sure the adjuster DOES NOT MOVE. After you’re done, check to see if the feeler gauge still feels the same. If it seems to have loosened, then undo the adjuster and tighten it down just a little and secure the adjuster nut. If it seems to have tightened, do the opposite.



Repeat the same process for all valves. It does not matter if you begin with intake or exhaust first.



This is all!







Now, although I’ve outlined a basic guide, I’ve found that often times what I talk about engine valves, people don’t know what a valve actually looks like or how it functions, so to understand what the adjustment is actually doing and why, I want to add some further FYI bits.


So, what is a valve?


Not this (hydraulic solenoid)




Or this (water outlet valve)




Or this (vacuum tube)




But this.





What does it do?

Being in Cambodia, many are probably familiar with “Suck, Squeeze, Bang, Blow”, also known as the Otto cycle. Here is an animation of how it works.

https://upload.wikimedia.org/wikipedia/ ... Engine.gif


The valve’s job is to seal off the combustion chamber area during the compression and expansion process. Simply put, open and close at the right time so the Otto cycle can take place. I wont get into the dynamics and science behind the valve timing itself in this post.





So, what does “adjusting” the valves (or rather valve clearance) mean then?

Adjusting the valves doesn’t mean adjusting the timing or where the valve is positioned, but rather, adjusting the arm that opens and closes the valve. It might be hard to grasp, so here’s an exploded engine view to see what we’re talking about.


Again, outside of the engine (what you can see).





Here’s what a typical horizontal motorcycle engine looks like.




Here’s what is inside of the engine (you can see the two valves now).



And here’s where the arm (called the rocker arm or tappet arm) pushes on the valve when the valve is commanded to open. It is the gap from this contact point that is adjusted (orange arrow). Gap is greatly exaggerated.






Now, you might be asking yourself, WHY is there a gap in the first place? What is the point of having a gap? Well, it’s very complicated once you dig into things, but long story short is that the engine “grows” when it heats up. This means that metal expands and clearances change as it does so. Ever put a bottle of water in the icebox when it’s half full? Ever watch it shrink? Same principle except on a much smaller scale.

However, to further explain why the correct gap is necessary, you have to understand how the valve actually works.

Firstly, let’s take a look at what happens when the gap is too big.





When the valve gap is too big, like above, when the cam shaft rotates to push the arm down and open the valve, you get a big “clack”. I’ve heard many reasons why people say this is bad, but in my experience with clacky valves, unless it’s extremely out of adjustment or causing an issue with power (like below would do), it’s not that big of a deal. It’s mainly annoying as people don’t like the sound of ticking valves (they think their vehicle is in bad condition).

If you contend that “any noise is bad”, listen to an air cooled VW or Ducati L twin and tell me it’s “not supposed to be that way”.

Either or, the reason valves are making noise (more so than usual) is because of the contact between the arm and the head of the valve.








Secondly, let’s take a look at what happens when the gap is too small or non existent (zero clearance).

**IMPORTANT, JUST BECAUSE YOUR VEHICLE IS NOT MAKING NOISE DOESN’T MEAN IT’S OKAY. IN FACT, THE WORST CASE SCENARIO IS HAVING QUIET VALVES. THIS IS WHY IT IS VERY IMPORTANT TO CHECK AND ADJUST YOUR VALVES REGULARLY, OTHERWISE YOU ARE FACING TOP END ENGINE FAILURE IF NOT DONE.




When the clearance is too small or at zero, this is where all sorts of problems occur. Why?

To understand why, we need to take a look at how valves function.




1st, look at the silver ring around the valve. This is called the valve face and it is where it contacts against the valve seat (the circle in the cylinder head) and seals the combustion chamber. However, it is also (unknown to some) how the valve cools itself off.

Imagine an ice cube. Pick it up. Because you picked it up, your hand is now getting cold because you’re touching the ice cube. Same with the valve, because it is touching the metal surface of the much cooler cylinder head (cooler than the expanding gases of the deflagrating petrol), it is protected from melting or burning. This is VERY IMPORTANT to the functioning of an engine because if a valve doesn’t have sufficient cooling time or contact with the cylinder head, the very hot gases in the engine will cause the valve to burn or melt, rendering your engine powerless.

Why is this you may ask?




Let’s go back to our zero clearance valve.




And now let’s go back to our cylinder head.




On some engines, what happens is that the as the engine heats up, the valve clearance “tightens up” even further than zero. The arm has negative clearance between it and the valve and the valve (exaggerated in the picture) ends up staying open or not sealing around the seat. When this occurs, there is no cooling of the valve. BAD. When this happens, the flames from the combustion chamber escape around the valve edges and very quickly, burn/melt the valve seat/face.

**When this happens, the only way to fix the problem is to replace the valves and recut the cylinder head**, i.e. A minor engine overhaul. This is what you want to avoid also.






So in essence, what is a valve adjustment?

A valve adjustment is the process of setting the valve clearance on your vehicle to “just right”. Just enough of a gap to ensure the valve does not burn, and not too big of a gap so it doesn’t make excessive noise, although if you’re a VW fan like myself, you know that a “tappy valve is a happy valve” because valves that make noise are a guarantee that you have sufficient clearance and that you run no risk of burning them.

So, what takes place in a valve adjustment then, what are you actually doing?




What happens when you’re adjusting the valve is that you’re moving the adjuster (the screw thing above) down towards the top of the valve stem.


This is the adjuster.



See how it moves up and down? This movement is what takes up the slack.







Now this whole walkthrough has been extremely exaggerated, meaning the pictures. This is strictly to show the operating principle. However, the real tolerances we’re talking about here are incredibly tiny. To give you an idea of just how tiny a different between “too much” and “oh shit we screwed up our engine” is, here’s a visual demonstration.




A human hair is roughly .1 mm thick. The intake valve adjustment on this motorcycle is a .04 mm gap.



To give you idea of how small that is, firstly, I can’t effectively zoom in on my camera well enough to demonstrate, and secondly, if you take a look at the size of the gap vs. the strand of hair, you’ll notice the gap is considerably wider. Now take into account that the hair is nearly 3 times wider than the gap of the arm to valve and now you begin to get an idea of the clearances we’re talking about.





For example, I’m willing to be that some of you missed that there was a feeler gauge in the last picture.





I hope this has been useful or entertaining to anyone reading. I wrote this in a quick moment, so it is by no means complete. If you have any questions or want to add or comment more, feel free. Any questions as well, feel free to ask me.


AE86/Akira S.

Top post Akira.