911SC timing and idle adjustment

[jcadwell]

I just finished replacing the permatune with an MSD ignition box in my 82 SC. The MSD seemed sluggish in comparison to the permatune, and the idle was different, but it otherwise runs well.

I went to verify the timing, and it is significantly advanced. (Distributor is twisted as far clockwise as it can go). If I set the timing to 5 degrees BTDC the idle is too low to run...

The Haynes manual says that the idle adjustment is too complicated for a mere mortal, so I need to take it to a dealer...

Does the idle require any special tools or know how? Or do I find a screw and twist?

[James Brown]

There is a big knurled screw on the left rear of the throttle body. turn to increase or decrease the idle.

[Steve@Rennsport]

Originally Posted by jcadwell

I just finished replacing the permatune with an MSD ignition box in my 82 SC. The MSD seemed sluggish in comparison to the permatune, and the idle was different, but it otherwise runs well.

I went to verify the timing, and it is significantly advanced. (Distributor is twisted as far clockwise as it can go). If I set the timing to 5 degrees BTDC the idle is too low to run...

The Haynes manual says that the idle adjustment is too complicated for a mere mortal, so I need to take it to a dealer...

Does the idle require any special tools or know how? Or do I find a screw and twist?

Make sure the green trigger wire from the SC distributor is properly connected to the MSD's green & violet trigger wire. Phasing is critically important otherwise the timing is about 10-12 degrees off.

[jcadwell]

I have the inner green wire connected to MSD green, and the outer sheath connected to the violet. I didn't check the timing before I did the replacement (permatune was not functioning correctly).

Right now I have the timing set at 5 BTDC at idle with both vacuum advance and retard hoses unhooked and plugged. I increased the idle speed from its previous setting, as the change in distributor position changed the idle speed.

The car runs well in the garage, and revs cleanly throughout the rpm range, then settles to an idle quickly.

I haven't driven the car since I set the timing, but I'm hopeful this setting is better.

Are there any 'seat of the pants' tests for proper timing?

[Walter_Middie]

Are there any 'seat of the pants' tests for proper timing?

Setting the timing at idle is a good start, but you should really set it at 25 degrees BTDC at 4,000 RPM, and check that it doesn't go any higher. The idle timing isn't that important other than to show you if your mechanical advance is working. If you have 5 deg at idle, and 25 at 4,000 RPM, then your advance weights are doing the right thing at the right time.

[schumicat]

I don't think the sc timing retard and advance are controlled by weights; they are controlled by vacuum. There are blue and red rubbery vacuum hoses attached to the distributor (I think blue is retard but don't recall offhand). Like another post says, the idle speed on SC is very easy to change using a large flattip screwdriver (on the 84+ it is controlled by the ECU). the idle speed affects timing a little and vice versa. when you mess with one you should check the other to confirm it is still w/in spec.

Originally Posted by Walter_Middie

Setting the timing at idle is a good start, but you should really set it at 25 degrees BTDC at 4,000 RPM, and check that it doesn't go any higher. The idle timing isn't that important other than to show you if your mechanical advance is working. If you have 5 deg at idle, and 25 at 4,000 RPM, then your advance weights are doing the right thing at the right time.

[James Brown]

Schumicat, the dissy on SC's has vacuum advance, vacuum retard, and mechanical advance. To check the mechanical advance, remove the vacuum hoses and increase to 4-6k like Walter says. Only way to check this.

[83_Silberpfeil]

Now that my SC has re-started (but still on jack stands). I want to get idle adjusted (too low at the moment), and verify/adjust the timing. So, I searched and found this old thread to revive.

QUESTION: when the instruction says, "vacuum hose disconnected", which lines to I disconnect? There are two attached to the vacuum module: one blue ; one red? Do I disconnect one or both?


I just ordered a timing light from AMZN, and will tackle this on the weekend.

Thanks!

[Flat6pac]

What it’s telling you is there is 2 separate lines of vacuum, one at idle and retarding the distributor and the other at full throttle advancing the distributor. The idle vacuum is correct if you feel vacuum at idle, as the hose is connected to the port below the butterfly
Quite often the pods are defective and don’t respond to the needs of the distributor
The counterweights in the dist are working if the timing advances.
On the 80-83, the pod connects to an outer rotational lever that many times are frozen and don’t respond to the vacuum. This you find out by removing the pod screws, pull and push on the pod to see rotation inside the distributor actually happens. If it doesn’t rotate, inside the distributor needs work to correct.
The 78/79 SC is vacuum advance only on the pod but the inside workings of the distributor are the same as above where removing the pod screws permits movement to be seen on rotation of the inside the distributor
Bruce

[83_Silberpfeil]

Thanks for the explanation Flat6pac. It helps me understand the general idea of what "the pod" does and how it interacts with the distributor.

So, one vacuum line is for idle retard, and other is for full throttle advance. I guess I'll have to each line and feel for vacuum at idle to validate which one is which --- that is if it is working properly.

Originally Posted by Flat6pac

What it’s telling you is there is 2 separate lines of vacuum, one at idle and retarding the distributor and the other at full throttle advancing the distributor. The idle vacuum is correct if you feel vacuum at idle, as the hose is connected to the port below the butterfly
Quite often the pods are defective and don’t respond to the needs of the distributor
The counterweights in the dist are working if the timing advances.
On the 80-83, the pod connects to an outer rotational lever that many times are frozen and don’t respond to the vacuum. This you find out by removing the pod screws, pull and push on the pod to see rotation inside the distributor actually happens. If it doesn’t rotate, inside the distributor needs work to correct.
The 78/79 SC is vacuum advance only on the pod but the inside workings of the distributor are the same as above where removing the pod screws permits movement to be seen on rotation of the inside the distributor
Bruce

[83_Silberpfeil]

Question: Should the TDC mark on fan housing be directly above the center line of the engine pulley?

Finally got garage time and checked the timing on my 83 SC.

I set my timing light to 5* BTDC. Then, looked for the Z mark on the pulley to match the TDC mark on the fan housing. As is, without any adjustment, timing seems a bit too advanced. But there's something that makes me question what I'm seeing.

I've tried to diagram this on the image below. The TDC mark on the fan housing doesn't look to be directly above the centerline CL of the fan pully. The TDC mark appears a bit to the left of the CL of fan pulley. In the diagram, I'm indicating that Point A looks to be to the left of Point B.

Back to my timing light check. As it is, the Z mark (w light set @ 5* BTDC) appears right at CL of the fan housing, and closer to CL of pulley. Could it be the fan housing rotated/slipped, or was just not installed properly?

Thanks!

[proporsche]

the alt.housing sits on a big pin so it is not likely moved..Also always check your timing when engine is warm..
Ivan

[83_Silberpfeil]

A quick follow up. For the timing check, I removed both vacuum lines attached to the pod on the distributor -- both blue and black tubing. Using my finger to block the end of the tubing, I was able to detect a bit of vacuum on the black line; nothing detectable on the blue line.

Is the black line for "retarding the distributor at idle" OR "advancing distributor at full throttle?

Thanks!

[83_Silberpfeil]

Hi Ivan -- thanks for your reply to describe how alternator housing is mounted. It sounds like, I should just trust that the alt housing TDC mark is correct, and adjust accordingly.

I'll report back again later today.

Originally Posted by proporsche

the alt.housing sits on a big pin so it is not likely moved..Also always check your timing when engine is warm..
Ivan

[Flat6pac]

If the fan housing is mounted off location, which is easy to do, you could be off on the timing by several degrees.
Instead of a drawing, post a picture of the fans housing line in reference to center line of the case. Very possibility you’ll need to loosen and reset the fan housing to proper location.
My posting pictures shows the reference and pin on a case and fan housing
Bruce

[83_Silberpfeil]

For the rest of afternoon, I was able to get the idle near 950 RPM, and set timing (gun/light @ 5* BTDC) and align the marks Z1 and alt housing TDC marks.

@Bruce - thanks for the comments and posting your fotos. They do help me visualize how the housing is mounted.

I will go back and look in the engine bay - check alt housing TDC mark & how it aligns w case center line.

I must say beforehand, it is so crowded back three, and dark. Really hard to find stuff let alone take a clear foto. But, I'll look for them and try.

[Flat6pac]

When you plug the hoses back on the idle will drop and the timing light will show you after TDC showing the correct hose is connected and the pod and distributor are working properly
You still need to know that the fan housing and case centerline are the same.
Bruce

[PeteKz]

The split between the case halves is the standard reference point for TDC. If the mark on the fan housing is directly on the case split, then it is correct.

For timing at idle, I disconnect both lines. Then set timing 5 BTDC. Then rev it up to 3000 RPM or wherever the timing mark stops advancing. The timing should then be close to 25 BTDC. Then reconnect the vacuum lines and check the TOTAL timing (mechanical + vacuum). It should be 33-35 degrees. Adjust the timing as needed to get this TOTAL advance.

[83_Silberpfeil]

Pete - I will check where the mark sits relative to the case split.

Thanks for the timing adjust/check procedure. I will revisit as well.

Originally Posted by PeteKz

The split between the case halves is the standard reference point for TDC. If the mark on the fan housing is directly on the case split, then it is correct.

For timing at idle, I disconnect both lines. Then set timing 5 BTDC. Then rev it up to 3000 RPM or wherever the timing mark stops advancing. The timing should then be close to 25 BTDC. Then reconnect the vacuum lines and check the TOTAL timing (mechanical + vacuum). It should be 33-35 degrees. Adjust the timing as needed to get this TOTAL advance.

[83_Silberpfeil]

@PeteKz - finally got back into the engine bay.

I looked for and found the engine case half/split line behind the fan housing. And, to best of my ability, visually verified that the TDC mark on the housing aligns w the case half/split line. Was quite dirty back there, but I used shop paper town and a flat screw driver to reach behind the housing and wipe down that area. The split/half line became more visible, and I was able to align, validate. But, too small of gap, and not enough light to take a good foto of what I saw/validated. I'll just have to go w what I saw. Thanks for helping/suggesting this.