Valve adjust-which takes precedence for TDC-rotor pointing at notch or Z1?

[89PS911]

Hi,

I am adjusting my valves and have a couple of questions.

In Wayne's 101 book, page 59, it says that that the Z1 mark should line up with the mark on the fan housing AND the distributor rotor must point to the small notch on the distributor housing for cylinder #1 to be at TDC.

On my car, the center of the end of the rotor's metal tip is pointing directly at the notch on the distributor housing only when the Z1 mark is a few degrees (~ 1/2 inch) past the mark on the fan housing. Alternatively, when Z1 is lined up with the notch on the fan housing, the right edge of the end of the rotor is just approaching the notch on the distributor housing (i.e. not really pointing at the notch).

Question 1: Which takes precedence in determining TDC -- Z1 lined up with fan housing mark or the center of the end of the rotor pointing directly to the notch on the distributor housing?

Question 2: Does it matter if I adjust the valves with the Z1 mark a few degrees past the mark on the fan housing (when the center of the end of the rotor is pointing directly at the notch on the distributor housing)?

For information, when rotating the Z1 mark (or any of the other marks at multiples of 120 degrees off of Z1) a few degrees before the notch on the fan housing and a few degrees past the notch on the fan housing the motor turns easily (including up to where the center of the end of the rotor is pointing directly at the notch on the distributor housing).

Also for information, both the exhaust and intake valves seem to remain closed in that sweep of a few degrees around when Z1 lines up with the mark on the fan housing, i.e. the ends of the rocker arms remain for both valves don't seem to move.

Thanks,
Jonathan

[trak ratt]

All things being equal Z1. On pre '84 cars the timing is set by moving the dizzy. So not lining up means it's either advanced or retarted. "84 and beyond timing is set by computer

[JJ 911SC]

Where is the dizzy pointing when at Z?

Mine is a bit before the notch but the same distance past the notch when I move the rotor to it spring loaded advance CW position.

[blucille]

I may be in the minority, but here's what I'll say...

It doesn't really matter.

Look at the lobes on a camshaft, they only open a valve for a short time, the rest of the time you can adjust the valve backlash, whether it is exactly at the right time or not, the only time you can't check the valve backlash is when the lobe of the cam is applying pressure on the rocker arm.

[timmy2]

Go by the crank pulley markings. They are mechanically set when the cams are set up.
The dizzy can be all over the place depending on timing adjustments.
The rotor pointing to the notch (or close to it) tells you you are TDC on cylinder #1.

[James Brown]

sonett43 your minority report is in the majority, it only counts when the cam lobe is not opening or closing the valve. don't get hung up on where the timing marks should be, just note the lobes position

[JJ 911SC]

As long as some of the metal end line up with the mark...

At Z:




At Z, Spring Loaded on Dizzy Expended:

[Walt Fricke]

The distributor mark is only useful for telling which TDC you are at. There are two of them for each distributor revolution, same as with the cams. So TDC firing (both valves closed) is the one where the rotor is at or near the distributor notch.

As to setting the lash, the fact is that at least half the rockers are on the base circle at any given time. If you have all four valve covers off, and don't like rotating the motor, you can do the ones which are on the base circle, rotate, and get the rest.

Naturally, how to-its (including the factory, I think I recall) say start with #1 at TDC firing to set intake and exhaust, then rotate 120 crank degrees and do the next cylinder in the firing order, and so on until you are done. That is a kind of safe harbor. But if the engine is in the car, it is also the one which calls for the most clambering around, under the car, up top, rotate, back under, up top, etc. With the motor on a stand, rotating is easy, but so is looking at the rocker - you can tell by looking if it is on the base circle, or if it is on a ramp. Plus if this is just maintenance adjustment, you know the valves which won't wiggle are not on the base circle, and generally the ones which will are on the circle if you are at 0, 120, or 240 on the pulley.

You only should worry if you face cognitive dissonance: you are at crank TDC, and the rotor is not near the distributor mark, but also is not pointing 180 degrees away from it. That usually means that the distributor is installed incorrectly. Though it could mean that the crank pulley has sheared its locating pin and is itself not where it belongs. Missed shifts can do this to the pulley.

[K Sykes]

Dizzy - because you can be at Z1 and be 180 off at the dizzy. It's a four stroke engine and your are at Z1 twice for every time the dizzy goes around once. If you were asking which is more accurate when you know you for sure you are at TDC, then Z1, but as someone else pointed out, it isn't that critical as long as you are off the lobes.

[89PS911]

Thanks everyone. By the way, forgot to mention my car is a 1989 3.2.

So if I can easily wiggle both elephant feet for cylinder 1 I should be fine adjusting both valves on that cylinder? Even if the Z1 mark is slightly past the mark on the fan housing while the rotor is pointing directly at the mark on the distributor rim?

[JJ 911SC]

Originally Posted by 89PS911

... Even if the Z1 mark is slightly past the mark on the fan housing while the rotor is pointing directly at the mark on the distributor rim?

Use Z1 on the mark with the rotor pointing in the vicinity of the the notch on the rim.

[Ronnie's.930]

Originally Posted by trak ratt

All things being equal Z1. On pre '84 cars the timing is set by moving the dizzy. So not lining up means it's either advanced or retarted. "84 and beyond timing is set by computer

Unless it is a Turbo/930 . . .

[Walt Fricke]

Yes, OK if Z1 slightly off. Both valves are closed for quite a ways on either side of Z1 firing TDC.

But we are all telling you to forget - that is just forget - where the distributor mark is pointing as long as it is close at all. Use Z1 for all your timing and adjusting work. All the distributor mark is good for as far as adjusting anything, really, is to tell you where in the 720 degree engine cycle you are.

Z1 is exact and precise. The relationship between the rotor and that mark on the distributor (which marks where the center of the #1 spark plug post is on the distributor cap) is not precise, and doesn't need to be. The tip of the rotor is wide for a reason.

[89PS911]

Thanks again to all of you. Will use Z1 and not worry about exact position of rotor, so long as it is pointing close to the relevant wire terminal.

Cheers,
Jonathan

[T77911S]

listen to walt.
the dist is only to get you started in the cycle or procedure.