[JRD]

I'm checking the valve adjustment on my 2008 TW200 with only 650 miles (I recently bought it used with less than 500 miles on it). Clearances are within tolerance (.002-.004" intake, .004-.006" exhaust). As I was getting ready to button it up, I rotated the engine to learn more about how the valves worked and here's what I found:



1. with the tdc mark centered in the sight window, both adjusters are tight.

2. after a 360 degree rotation and with the mark again centered in the window, both adjusters are loose.

3. after another 360 degree rotation and with the mark again centered in the window, both adjusters are tight.

4. after yet another 360 degree rotation and with the mark again centered in the window, both adjusters are loose.



Based on my limited knowledge, this was not what I expected. The bike seems to be running well and the adjusters required no adjustment from me when I just checked them. I'm assuming that all is as it was when the bike left the factory.



Any explanation or insight will be appreciated. Hopefully this is the way it's supposed to be except that I need to learn more about how a single cylinder four-stroke engine works.



Joe

SW OHIO USA

 

[Rainman]

I'm no expert either, but I know that its crucial that you check the valves at TDC on the compression stroke. Any other combination of engine revolution and stroke will give you a false reading.

 

[Lonesome Dave]

It says some place on this forum, that you have a fifty/fifty chance once you line up the TDC marks. If you can't get the feeler gauge (.004) to fit, your on the wrong side and need to rotate 360 degrees. Then you will be on the compression stroke at TDC to do your checks. BUT, wait until someone else confirms this before you take my word for it!

 

[old mad max]

That's normal for a 4-stroke single................ Now if it were a smoker then it would be on a compression stroke every 360 degrees. OMM.

 

[elime]

I think a better mark to use is the one on the large cam sprocket. With it you get it right every time. Simply place the mark at 12:00 as shown in the picture then adjust your valves.



Replace the Phillip head screws with some bolts for easy removal. Get a new large o-ring in before you take the cover off in case you need to replace it. With a new o-ring simply tighten the bolts until it is metal to metal contact and then tight just a teeny bit more. Don't go any tighter though the temptation is difficult to resist. Or use a torque wrench.



If you do your 360 degree exercise you will notice the mark is at 12:00 then 6:00 then 12:00 again. You can only adjust the valves when the mark is at 12:00.

 

[RockyTFS]

Hopefully this is the way it's supposed to be......

Joe

Yup, that is exactly how it works. Find the mark, and if the feeler won't go in, rotate one revolution. To help avoid going past the mark, stick a pencil in the spark hole so you can tell when the piston is close to TDC.

 

[JRD]

I'm no expert either, but I know that its crucial that you check the valves at TDC on the compression stroke. Any other combination of engine revolution and stroke will give you a false reading.

With all respect, it seems to me that if the valve is closed with adjuster loose and the adjustment is within spec it shouldn't matter which stroke it's on. A closed valve is a closed valve, or am I missing something?



Thanks all for the feedback...

 

[RockyTFS]

A closed valve is a closed valve, or am I missing something?

Yes.



The idea is to get BOTH rocker arms loose at the same crank position. That only happens at TDC on the compression stroke. Oh, BTW, there is an easy way to tell which stroke is the compression stroke....put your finger over the spark plug hole. When you get pressure the piston is coming up to TDC on the compression stroke. Then look for the mark to get it right at TDC. EXACTLY on the mark, you only have to be a millimeter off to affect the feeler gauge reading.

 

[silverhead]

suck, squeeze, bang, blow. You want to time it right between the squeeze and bang. The issue with 'a closed valve is a closed valve' is that the profile of the camshaft might slightly vary at any given part of the cycle.



I found a photo of a TW camshaft and drew an imaginary line where maybe the intake and exhaust valves are both closed at TDC. That point gives you the proper values with your feeler gauges.



Everywhere I drew a red circle, the valve would be closed still, but I have no idea if it would yield the proper reading with the feeler gauge. Probably close, but I never try to out-think the manufacturer.

 

[elime]

A closed valve is a closed valve, or am I missing something?

At top dead center of the exhaust to intake stroke both valves are open a little bit. It is called overlap. On high performance engines the overlap is a lot hence the rough, lumpy idle.



Or think of it as the exhaust valve closes after TDC and the intake opens before TDC. Top dead center on the wrong stroke neither valve is closed.

 

[JRD]

You guys are amazing, thanks for the explanations. I'm going to look for some good pics or videos of a "visible engine" to help in understanding.

 

[frog13]

Yea,putting a ( object) pencil,straw,pen etc. in the spark plug hole,you can watch the object move upward.

 

[trailscout]

4 stroke fires every other time. Valves are both closed at the top of the compression stroke. Exhaust is open but closing with intake starting to open at the top of the exhaust stroke. Therefore both are tight on the cam. The animation shows an injector which we of course don't have. Yet. Plus it shows bucket and shim valve actuators instead of rocker arms. But it still shows why the valves are loose at only one of the two top dead centers.

Kudos for wondering how it worked.

 

[JRD]

Love the 4-stroke action diagram and will show it to my five year old grandson just for fun. He's very interested in how things work and has started making some simple Rube Goldberg machines with Tinkertoys and such.

Happy Thanksgiving to all!

 

[GaryL]

Love the 4-stroke action diagram and will show it to my five year old grandson just for fun. He's very interested in how things work and has started making some simple Rube Goldberg machines with Tinkertoys and such.

Happy Thanksgiving to all!

I Urge you to Encourage the young fellow! That desire to understand how things work is what starts it all and 10 years from now he will be here with us maybe digging in to Grandpa's old TW. I told a short story of my beginnings over in the Essay Contest thread and I have been a motor head ever since or at the least a Jack of all Trades but Master of None. You might also save him some future grief by implanting this statement in between his ears, "If it aint broke, don't fix it". He will have some trials and errors to go through and just like the rest of us he will open up some working device to see what makes it tick and have springs and all sorts of other stuff fly out all over his room. If he can find all the parts he will work very hard at getting it all back together. A good mechanic gets it done right when there is no extra parts left over and it works!

GaryL

 

[trailscout]

Love the 4-stroke action diagram and will show it to my five year old grandson just for fun. He's very interested in how things work and has started making some simple Rube Goldberg machines with Tinkertoys and such.

Happy Thanksgiving to all!

When my oldest son was not much older than 7-8 I bought him an electric engine model that when assembled did the same as the animation with four in line cylinders. Spark plugs sparking and the whole deal. (i may have got it partly for myself hee)

 

[trailscout]

Here's one for your grand son slowed down a bit. I can slow it down more if he needs it.

Edit: Appears you need to click the pic to get it to turning.

 

[JRD]

Here's one for your grand son slowed down a bit. I can slow it down more if he needs it. View attachment 2258

Edit: Appears you need to click the pic to get it to turning.

Thanks!