Question on Valves/Compression Stroke

[marcmiller001]

Hi gang,

I saw this quote below - after I followed my Clymer manual to set valve clearance and it made me a little nervous... when you rotate to OT... how do you know if both valves are closed on that side? I am thinking I want to go back out and check my work now! So how do I know if the piston I am working on is on it's compression stroke? Is it on the markings on the carrier?


The OT mark means Top Dead Center (TDC):   That point, exactly, when your motorcycle pistons are fully outwards.  OT, in German, is Oberer Totpunkt, more correctly translated as the top dead point.  OT is used when setting the valves.  Pistons in Airheads are two strokes away from each other in timing & valve operation. Both pistons are at the SAME position, in or out of the cylinders, at all times.  Proper procedure is to check/set the valve clearances at the OT mark.  That piston must ALSO be on its compression stroke; where both valves of THAT cylinder are closed.  BOTH cylinders can NOT be put on the compression stroke at the same time.

[Barry]

For me they make a simple task sound much too complex. There is no need for them to talk about compression stroke because at OT only one of the cylinders will have both valves closed.

I set the engine to OT and look at both cylinders. One will have both valves closed and when you feel the rockers there will be some movement. Set the clearances on that cylinder.  Rotate the engine 360 Deg and set clearances on the other cylinder. It's that simple and almost impossible to do wrong.

[marcmiller001]

THAT is the answer I was looking for - thanks Barry! Will go check my work today

[georgesgiralt]

Marc,
If you remove the TWO valve cover at the same time, put your engine at TDC (OT mark) and then try to move one rocker at the valve (exhaust is better because it should have more play). On one side the rocker won't move because it is in contact with the valve stem and on the other cylinder, the rocker will move a little bit because it has some play. It is this side you should adjust. Turn the crank a whole turn and then the other cylinder has got the play .... And is ready for adjustment.
We ar every good at comparison, not at absolute measures....

[nhmaf]

It is also easy to check for the ability to turn the push rods with your fingers if they are not under tension.  Both should be free to rotate on the cylinder with both valves fully closed.

Of course, if you have seriously closed up valve clearances or the previous person has buggered up the valve lash (it has happened) then  I rely on the OT mark AND the relative positions of the push rod ends , rockers, and distance of push rod extension above the head.

Most all the time though, the simple check above is all that is needed with regular maintenance checks.

[Justin B.]

I just stick my thumb in the spark-plug hole to determine compression stroke then a straw or wooden pencil to feel when the piston is at the top...

[wilcom]

You really don't have to be TDC, there is a bunch of room for error. I grab the push rod and it it isn't going up or going down, it's on the back of the lobe and the back of the lobe is all the same.

What ever side I start with I just roll it over till that valve is on the back side of the lobe ( not going up or down) and adjust away. If you look at the profile of the cam , you can see that more than 1/2 the distance around is all adjustable territory............. maybe I've just been lucky :-/

[Barry]

...Most all the time though, the simple check above is all that is needed with regular maintenance checks.

I did my annual spring service last week and it turned out to be just a check. None of the clearances needed any adjustment and  even the ignition timing was still spot on. Although it was hard,  I managed to resist the temptation to mess with anything.   It doesn't get much simpler than that.

Another area where I'm moving from replace as a matter of course to inspection and check is the transmission oils. I'm done with draining out low mileage spotlessly clean oil and not even finding any fuzz on the magnets. It's got synthetic 75W90 in and next  year I will check the levels and take a small sample with a syringe. If it looks clean it's staying in and will only be changed  every 3 -5 years. I know I've said this before but next year I'm really going to do it.

[Motu]

I don't bother with the confusion - left intake wide open, set the right intake, and so on.  So much easier, and you are always on the back of  the cam.

[wilcom]

I don't bother with the confusion - left intake wide open, set the right intake, and so on.  So much easier, and you are always on the back of  the cam.

Good method Motu....... limited thinking and much precision. What a great combination!

[mrclubike]

If you set the valves in What is called "Cross Over" Instead of top "Top Dead Center Compression" they will just be very loose and noisy they wont be be tight.

[Barry]

I've got to say that while I understand all the theories for different methods, I don't see how any of them are easier than using the BMW specified method which is setting them at OT.  Or how anyone could do it wrong with that method.

What ever method is used the most import thing is consistency of clearances between cylinders.  The actual gap isn't that important to the nearest one or two thou as long as the other cylinder is as close to being exactly the same as you can get it. By doing that you are making sure the valve timing and lift are the same for both cylinders.

[Tony Smith]

I've got to say that while I understand all the theories for different methods, I don't see how any of them are easier than using the BMW specified method which is setting them at OT.  Or how anyone could do it wrong with that method.

Old eyes and the need for a very bright torch to see the OT mark for one. I put a drinking straw down the plug hole and use it to determine TDC  with both valves closed. Quick, dead easy and no failing eyes are harmed in the process.

[wilcom]

Old eyes and the need for a very bright torch to see the OT mark for one.

Amen

[Barry]

Yea my eyes are old too. 

I have reading glasses in 1.0, 1.5, 2.0 and 3.0 dioptres according to how much light there is and how close I need to get to something. The OT mark is a 2.0 or 3.0 job and I've got to look at the timing marks anyway to check ignition timing so it's no trouble.  I have an LED on a flexible wand which is ideal for lighting in narrow spaces.