non-points distributors question

[Kurt B]

My 84 doesn't have points obviously. Instead, there's just a couple of things that, as the timing lobes cycle, they spread out and contact 2 flanges on the side.
Okay, so the spark comes down from the coil and is passed in turn to each of the spark plugs. Now I assume the when these things (like a pair of scissor fans or something) spread, they contect the outer flanges and that completes the coil/plug circuit I assume.
Now, the problem is, they're smacking it away too hard. I never heard this tapping before, and I realize now the reason I hear it is because the bad injectors were so bad, my car really sounded like a 60s chevy, concealing the noise...this is a guess, could be a valve, have no clue.
Anyway, The spring things are worn, but not broken as I first thought. What is causing them to smack the outer flanges so gdamned hard? Is this a problem in the distributor? And according to Porsche, there are two replacable components in the distributor: the cap and rotor (thanks krauts!).
If anyone looks into their distributor in the future, do something for me.
With the cap and dustcover off, go crank it. Do you hear it go tap tap tap loud?
Also, note the flanges. Twist the main shaft backwards, when you do, the scissors will swing out and hit the flanges, Is there wear on the flanges? Mine quite a bit of wear...it's eating right into them.



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Kurt B
1984 Carrera Cabriolet
911 Page
carrera_cabriolet@yahoo.com

[BRAINIAC]

Kurt, that mechanism is the mechanical advance. What it does is turns the rotor and trigger wheel (the latter is the trigger that tells the control module when to fire the spark) (rough translation) advanced in relation to the crankshaft to advance the spark as the rpm's increase. The faster the dist. spins, the more the weights are flung outward, which turns the rotor and trigger wheel more advanced.

If there is excessive wear on the weights where the pins rub, it may be time for a new or rebuilt dist. If it is minor wear, you can disassemble and lube the mechanism. Check the archives for the dist. spring thread. Someone mentioned they are available from Stoddard. I would suggest replacing the springs as well.



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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[BRAINIAC]

Oh, one more thought Kurt. Is it possible that you are hearing the tapping noise that high voltage spark makes as it arcs to ground? In other words, try it again with the coil wire going from the coil tower directly to ground so it doesn't arc. If that's not it then make sure that the trigger wheel isn't making contact with the pick-up coil. Shoot, I can't remember if those are Hall effect or pulse generator type distributors. I'll check my manuals and get back to you.

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[BRAINIAC]

OK, Duh! That's DME. You don't have any trigger wheel in your dis. It's all run off of the timing wheel on your flywheel. Sorry, it's late and I've been working too much.
Now my question is, why is there a mechanical advance in your distributor? On DME equipped cars all the dist. does is direct the spark to the correct cylinder. The computer should control advance.

Sorry for the above confusion. I was picturing an SC distributor in my mind when you described the inner workings of your dist.

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[This message has been edited by BRAINIAC (edited 07-03-2001).]

[This message has been edited by BRAINIAC (edited 07-03-2001).]

[BRAINIAC]

Alright Kurt, so what's up? Has your distributor been swapped for a different year dist.? I'm 99% sure that you should NOT have a mechanical advancer in your dist. on a DME equipped car.

If it is an SC dist. that someone modified to fit your car then you now have a mechanical retard! SC distributors turn backward from the other models! Is there an electrical connector on the side of your dist. that isn't hooked up to anything perchance?

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[Kurt B]

Hmm...okay, keep in mind I have the old oil cooler too...my car was made in Fall of 83, a very early 3.2 Carrera. God only knows what changes were made there after.

Anyway, there's not wires coming in or out on the side of the distributor...I will get a picture of the inside of it tonight.
But there are two springs, and two halves that are centered on a lever in the middle. You can turn the shaft backwards, and the halves will swing out and touch the outside posts...
Cranking the car with the coil disconnected causes whatever tapping to occur...it seems to be coming from the distributor...
I'd like to know what's in the bottom of a DME distributor...nothing? Just the shaft and it goes into the engine without any springed plates or posts or anything like that?
Now to me it seems that those posts are for the ground...I'm guessing the coil can't be grounded anywhere else..at the instant the spark goes from coil to rotor through the spark wire, into the plug, then back up through the frame, to the posts, through the to spring plates, and back up to the rotor..that's my guess on the circuit, but I don't know!

I very much appreciate your help here Brainiac! thanks


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Kurt B
1984 Carrera Cabriolet
911 Page
carrera_cabriolet@yahoo.com

[BK911]

Hey Kurt, I can't remember who wrote it or where it was posted, but it was from one of the big three who frequent this site and was about the mechanical advance in the carrera's distributor. Sorry to be so vague, but it's either here or Rennlist. I have to go or I would help do a search.

Good luck!
BK

[BRAINIAC]

Kurt, I think I have confused you. What you are describing is definitely a mechanical advance mechanism. It has no current going through it. What I meant about grounding the coil wire was to see if you weren't mistakenly hearing the Zap from the arcing spark with the cap removed. Capiche?

Now about that advancer. The only reason for there to be an advancer in a DME distributor would be to keep the rotor pointing at the 6 different poles in the cap more accuratly. That seems kind of unnecessary to me. The computer does all the advance and retard duties and uses the reference signal from the crank angle sensor on the flywheel. (remember those "chips" that alter the ignition curve and fuel curve?) That's why there aren't any "guts" in your distributor. And I'm still wondering why there is a mechanical advancer in there. WIERD!

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[Kurt B]

Thanks brainiac. Well what it does mean is that I can put some rubber or something over those posts and then start it (if it was part of a circuit it wouldn't start so I didn't, but since I'd not, I can), and if the noise goes away, bingo, I found the problem. If it's still there then it's back to the drawing board. I'll let you know if it goes away when I do this.

[twin plugged targa]

Hi Brainiac/Kurt,
I have been busy working but saw this thread as have had distributor woes and thought I'd investigate further!.
I too have the advance mechanism in my '86
so whats the deal?
Maybe there is no such thing as a Carrera Distributor!.
Or maybe I had someones old SC dist. thrown in there!.
rgds Ben

[BRAINIAC]

Please. Someone. Explain to me why a DME equipped car needs a mechanical advancer!!!!!!!!!!!!! My brain is burning fuses!!

OK Kurt, now that 86rgtp has confirmed that the advancer is supposed to be there. What I said earlier about lubing and replacing the springs still applies. However! What you may be hearing is the weights snapping closed! When you crank the engine with the starter, the RPM are very uneven. fast-slow-fast-slow.
So the weights are going to fling out then the springs are going pull them back in. This is probably why you are hearing the tapping. With the engine running, the RPM are higher and smoother. Therefore the weights don't tap in and out like they do when cranking. You follow? (Damn. I still don't get why DME needs a mech advance. )
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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet

[This message has been edited by BRAINIAC (edited 07-03-2001).]

[This message has been edited by BRAINIAC (edited 07-03-2001).]

[Ned, NYNA 11]

Brainiac,
Sure the DME controls the spark timing and as the engine speeds up, the spark fires earlier in the cycle. However,since the distributor rotor MUST be in line with the connector on the side of the cap when it fires, the rotor then must be advanced otherwise the spark would miss the connector.
That's why there is an advance machanism.
Ned Monaghan

[Roland Kunz]

Hello

Mechanical Advance is needed as the spark point will move ahead and if the distributor is solid the gap will get wider untill the spark will not jump anymore.

You can test it out by pulling the distributor and set it by one theet forward. Now your engine will rev up to 4000/min and then sounds like a machinegun.

The distributor needs regular maintance ( oil in the middle and on the fullcrum wights ). Also the finger and cap are mostly shoot after 20 - 30 000 miles.

The next Motronic generation could run direct from the coil.

The 3,2 was 1983 one of the first Motronic car on the road. Remember in 1983 the first XT/AT with a 286/8 MHz 8 bit board hit the marked. A VC 64 or Atari 800 was the best for low budgeds.


AHHH your problem can be checked as prevoius said. Sorry I´m not one from the big tree but I try to get in the top 10.

Grüsse

[BRAINIAC]

Well that makes sense. That's the only thing that I could come up with as a logical explanation. The thing that was bothering me was the fact that the 4cyl. DME VWs don't have them and neither do the C2/C4 and later.

Then I thought about how 4 cyl. have more room between the poles and can therefore run a wider rotor tip. And of course the 964 and later use twin plug which only requires half the ignition advance of single-plug, so the rotor doesn't need to advance as far.

OK, now I can sleep at night. Thanks!

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Tyson Schmidt
72 911 Cabriolet
92 C-2 Cabriolet