Wrapping up my head job and I have 3 questions

Fellow aficionados

Other than figuring out the meaning of life I have 3 other questions …

1 How do these intake manifold gaskets go ? The middle dark gasket is actually a thick spacer which is sandwiched by the upper and lower green gaskets. Both green gaskets are identical and have a light green smooth side and a darker slightly textured side. I have no idea if the darker green or light green side go against the spacer ???

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  1. I simply can’t figure out where the end of the hose (#1) coming off the oil filler tube goes ?

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  1. Something I’ve never thought about until I put my distributer back on. How is the timing set ? Although I’m totally comfortable that the distributor is back where it should be (I took a lot of pictures before I removed it) there aren’t any indexers on the engine damper so how is this done ? The distributor clamp has a slot so you can rotate it sightly before you tighten it down obviously to adjust the advance and retard of the spark … what’s up with that ?

Question #2 solved :grin:

The reason I couldn’t find a pipe nipple to attach the hose to was … it’s on the valve cover !!

Now any ideas on questions 1 and 3 … Hmm

#3
The engine will set its own timing automatically as long as you are installing the distributor per the shop manual. I replaced my head gasket last year on my '90 XJ40 and had no timing issues .
#1
I don’t remember worrying much about the green intake gaskets. Car started right up after the work.

Sounds like you are getting close to the end. Good luck

When I re-installed my intake manifold last month, I replaced the SINGLE paper gasket with another SINGLE gasket (no spacer etc) - maybe your kit had some ‘extras’ in it?

As per Jamie’s post the CPS picks up the timing from the reluctor wheel, the missing tooth tells the ECU where the crank is.
Immaterial as to which side goes where on the paper gaskets.

BTW, I also had two green gasket and the black insulator plate.

Jamie and Robin …

First thanks for the input. But I’m still a bit confused as how the timing actually works.

As I understand it the spinning rotor which is always energized by the coil sends out an electrical impulse to a spark plug every time it passes a terminal on the distributor cap. And that determines when each spark plug fires… OK so far ?

So the only thing that can actually determine when each spark plug fires is the physical relationship of the rotor and the terminals in the cap. I can easily understand how a car with a coil pack can change when the signal is sent to the spark plug by the computer, but how can a computer change the physical relationship of a distributor and it’s cap to adjust the timing ?

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Dennis,

The ignition timing is determined by the EMS ECU based on a signal from the CPS telling it where a piston is in its progress up the cylinder on the firing stroke of that cylinder (i.e when both valves are closed).When the ECU tells the coil to generate a spark, it travels down the king lead to the distributor and from there across the rotor arm which (hopefully) is pointing to the plug lead pick-up for that same cylinder.

The small movement of the distributor in its fixing slot merely increases or decreases the gap between the curved tip of the rotor arm and the plug lead pick-up in the cover to slightly delay or advance the spark as it jumps the gap.

Bryan, hello mate …

You stated that “The small movement of the distributor in its fixing slot merely increases or decreases the gap between the curved tip of the rotor arm and the plug lead pick-up in the cover to slightly delay or advance the spark as it jumps the gap.”

My question is how do you determine what that “slight delay or advance” should be with no timing marks since it’s a physical adjustment not a computer controlled one.

Groove, STOP :slight_smile:
The spark, as described by Bryan is generated by the ECU, the position of the dissy cap/body is only critical in that if the dissy is too far out of position the spark can miss the post its supposed to jump to when the ECU is advancing the spark.

If you know for certain your crankshaft is top-dead-center on #1cylinder, install the distributor making sure the rotor arm is aligned with the lead to #1 cylinder and let the ECU figure out the exact timing necessary for the engine’s running conditions.

Thanks guys …

I’m "almost " there :cowboy_hat_face:

So the computer (based on all it’s inputs) energizes the rotor when it determines it’s the optimum time for that spark plug to fire, am I correct.

And, the slight physical adjustment of the distributor has nothing to do with the timing other than to insure everything is in the ballpark when the computer decides to fire it. I hope I’ve got it because it all makes great sense.

Here’s a picture of my distributor at TDC. This would explain why the tip of the rotor is so wide, so that whenever the computer decides to energize the rotor it is still adjacent to the proper cap terminal with room to slightly increase or decrease the “timing” of the spark.

NOW THIS MAKES SENSE !

Groove et al, let me float this thought and all y’all can take pot shots at it. I took a photo of my distributor with cap off and rotor on.


Then I enlarged it until the diameter of the dizzy measured 60 units (mm). The tip of the rotor measured approximately 10.5 units. With a diameter of 60 units the circumference is 188.5 units, so the tip of the rotor is about 5.57% of the circumference of the dizzy. 5.57% of 360 degrees is about 20 degrees. Let’s assume the signal to fire the coil is sent when the center of the rotor tip is aligned with the center of the contact in the dizzy cap and that is also when the cylinder is at top dead center (TDC). If the signal to fire the coil is sent at either of the extremes, that is when either the leading or trailing edge of the rotor tip is aligned with the contact in the cap, you would be half of 20% or 10% before or after TDC. Or so it would seem. Commence taking pot shots!

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Dennis,

Yep - that’s why the ignition timing is always expressed as ‘degrees before TDC’ and the rotor arm should be pointing directly at the pick-up for the plug lead of that cylinder at that number of degrees before TDC.

Just to muddy the waters here, timing will vary quite a bit between engines and even for the same engine it can vary depending on whether it is driving a manual or an auto transmission. For example, for these Chrysler inline six cylinder engines (source: https://www.allpar.com/mopar/V6/slant-six-specs.html):

1968 Slant Six Timing

                           |**170 Manual**|**170 Auto.**|**225 Manual**|**225 Auto.**|

Timing (Degrees)| 5ATC | 2.5 ATC | TDC | TDC |
|Timing (@RPM) | 700 | 700 | 650 | 650 |

Note these are base timing specs at the RPMs shown; as engine RPM increases the timing will be advanced. These engines were in the same ‘family’ with the same cylinder bore (3.4 in.) - the 170 cu. in. engine was a short (3.125 in.) stroke version while the 225 was a longer (4.125 in.) stroke version.

Mike …

Looking at the two pictures of our distributors it appears that both rotors are at TDC (I know mine is) as far the relationship to the A/C muffler

But I’m surprised at the different positions of the distributor body. The notch that my arrow points to is the #1 plug position on the body. Im puzzled that your distributor body is rotated counter clockwise quite a bit and not lined up with the #1 plug ? Of course if your distributor shaft was inserted on a different spline and the rotors not positioned at TDC that would explain it.

Groove, we may be comparing apples and oranges here. I do not know whether my engine was at TDC when I took the photo of my distributor (I am going to posit it was past TDC) as I just ran out to the car, popped off the dizzy cap and snapped the picture. The A/C compressors and mufflers are different between your '89 model and my '94 which may account for the differences you are seeing.

Mike …

Right you are sir ! I don’t even know why I posted that :confounded:

Because you could :slight_smile: looks like you are ready to fire it up.
That’s always the time that theres an involuntary rectal movement for me :slight_smile: