Really really stupid questions about distributor and timing

[sugarwood]

I am trying to understand this video.
I remember trying to learn about this a few years ago, but have entirely forgotten what little I learned.

How does he know "she's pointing to #1" ?
But, the rotor is not pointing to anything, as the cap and wires are removed.
Why is he yanking on the wires?
How does he know which wire the rotor is pointing to when the cap is not even attached?

After that, he is trying to see if #1 is at TDC?
Why is he looking for no movement around TDC?
At TDC, both valves are closed and there is no movement?

On the 911, TDC notch on the pulley means either #1 or #4 is at TDC.
Without pulling the cap, how do you know which one is at TDC then?

Why is he even looking for #1 TDC? How does that help him start the car ?

[HarryD]

Originally Posted by sugarwood

I am trying to understand this video.
I remember trying to learn about this a few years ago, but have entirely forgotten what little I learned.

How does he know "she's pointing to #1" ?
But, the rotor is not pointing to anything, as the cap and wires are removed.

He is looking at where the rotor is pointing. If you look at the cap, it is approximately in the same place at the #1 lead.

Why is he yanking on the wires?

to be sure #1 is going to the correct place on the cap.

How does he know which wire the rotor is pointing to when the cap is not even attached?

see above

After that, he is trying to see if #1 is at TDC?
Why is he looking for no movement around TDC?
At TDC, both valves are closed and there is no movement?

I am assuming the valve cover is off and he is verifying that the valves are both closed.

On the 911, TDC notch on the pulley means either #1 or #4 is at TDC.
Without pulling the cap, how do you know which one is at TDC then?

see above

Why is he even looking for #1 TDC? How does that help him start the car ?

If the timing is way off, the car will not staert or backfire causing other damage.

[sugarwood]

Thank you.
If no one messes with the distributor, how does the timing become "off"?

[Paulporsche]

As the points wear down, the timing becomes more retarded.

Looks like someone installed this distributor incorrectly. At first he checked the rotor compared to the wire leading to cyl 1. Next he compared the rotor to the notch in the distributor and/or on the timing pulley.

[Trackrash]

There is a line on the distributor body visible when the cap is removed that indicates #1 firing position.

On a points controlled ignition, like on VWs and 911s up to '77, the timing can change depending on the wearing of the points.

[smadsen]

You can also find #1 TDC by removing the spark plugs and have a helper turn the engine, BY HAND, in the correct direction of rotation. Place thumb over the spark plug hole and feel for compression. Now you're coming up on #1 TDC (not #4). Wait for the timing marks to line up. Viola! TDC, #1 firing.

If you can easily use a degree wheel, then use an engine stop thru the spark plug hole. Make the stop by breaking the porcelain part out of the threaded metal part of an old spark plug. Run a tap thru the metal. Insert bolt. SLOWLY turn the motor by hand until the piston "bonks" the inserted bolt. Take a degree wheel reading. Turn the motor back to "bonk" again. Take a reading. Total degrees, divide by 2. Viola. Dead nuts TDC. Good idea to always check the factory TDC when building a motor. Beware, the valve can interfere with this method, so never force anything.

Or you can just watch the intake valve close up on #1 and then keep rotating to the mark. 'Course you gotta remove the valve cover for this one. Or the intake manifold.

[sugarwood]

A few years ago, I attempted a valve adjust but chickened out. As a short cut, my mechanics told me to check for slight play in the rocker arm at TDC (good). I remember at the TDC notch, either #1 or #4 was actually at TDC, since 6 cylinders, and 360 degrees. What I can't remember is how I knew if #1 was at TDC or if I had to spin the crank pulley another 360 to then make #1 TDC. I did not have spark plugs removed, just the valve cover removed.

[Walter_Middie]

Sugarwood,

Let's look at an example where #4 is at TDC and #4 spark plug is about to fire. Cylinder #4 has just finished intaking a fresh charge of fuel and air, and #4 piston has come all the way up to the top of the cylinder, compressing the charge and is ready to ignite when the spark plug fires. At this point, both the intake and exhaust valves are tightly shut to seal against the compression. If you remove the upper valve cover on the side of the engine for #4 and check the intake rocker arm, it will be loose, as the valve spring is holding the intake valve shut and the rocker arm is not being used at this time. No need to check the exhaust, but it would be the same - valve closed, rocker arm loose.

Now let's look at what #1 is doing at the same time that #4 is about to fire. Cylinder #1 is exactly opposite from #4, and #1 piston is also at the top of its cylinder - this is where everyone gets screwed up - when both #1 and #4 pistons are at the top of their cylinders. The difference in this example is that #1 has just finished exhausting the spent combustion and is about to intake a fresh charge of fuel and air. Both the intake and exhaust valves are slightly open, and both rocker arms have a load on them Take off the upper valve cover on this side of the engine and you will see that the #1 rocker arm is tight. Same for the exhaust valve, but you don't need to check that.

So you only need to remove the upper valve cover on the side of the engine with cylinder #1. When the engine is in the correct position of #1 at TDC, the rocker arm for #1 will be loose. If it is tight, rotate the engine crank 360 deg to where #1 is again at the top of its cylinder. Now the intake valve should be closed and the rocker arm loose.

[sugarwood]

Rex,
Thanks for the excellent explanation.

At TDC, rocker is loose, like in the video, right?



https://www.pelicanparts.com/techarticles/911_valve_adjust/911_valve_adjust.htm

[sugarwood]

Refresh my memory, if one is doing a valve adjust (I am not), and they are done with #1 TDC, how do you know to rotate it 120 degrees?
There are 3 total markings on the large round pulley ? 1,6,2,4,3,5

[Walter_Middie]

Sugarwood,

For your 3.2 engine, the crank pulley should have markings at Z1, 120 deg, and 240 deg. Like this:



Your firing order is:



So you adjust #1 when the pulley is at Z1 AND #1 is on its compression stroke and ready to fire (rocker arm is loose).

Adjust #6 when the pulley is at 120 deg
Adjust #2 when the pulley is at 240 deg
Adjust #4 when the pulley is once again at Z1 - but this time #1 rocker arm is tight and #4 is loose
Adjust #3 when the pulley is once again at 120 deg
Adjust #5 when the pulley is once again at 240 deg

Back to #1 at TDC when the pulley is at Z1 and #1 rocker arm is loose. You've now rotated the engine crank pulley around twice.

[sugarwood]

Thanks for the replies.

While on the subject, when the valves DO need adjusting, what do they feel like without the feeler gauge? When on TDC #1, will the rocker arm be too loose? Or too tight? What is the "symptom", or can you not tell anything this way?

[Walter_Middie]

The valves can be either too loose or too tight. There is a range where they are OK, and in general, the rocker arm should feel slightly loose. Usually, the valves get too loose, and you will hear more clacking than usually when the engine is running.

Experienced mechanics can do this with feel alone, and don't need to measure the gap. They just know how loose they should feel.