Help me understand dual points?

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JAV
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Help me understand dual points?

Post by JAV »

I'm new to the Colombo v12 and have been studying the ignition system and while I know it works, I must admit I don't understand how.

I'm fairly adept at electronics and understand how a normal coil / contact points system works... the swtiching off (or opening of the points) causes a loss of the ground source to the coil which collapses the feild and generates a voltage spike.

What has me stumped on the Ferrari schematic is that both breaker points in a single distributer are connected to the same negative coil lead (through the resistor). Then, it appears each of the points are opened individually by the 3 lobed cam... which means one set of points or the other is always closed, and thus providing the groung path to the coil. This begs the question.. how the heck does the coil fire if there is always a ground connection?

Am I missing something? Do both sets of points have an open overlap that I'm not seeing?
John Viveiros
1964 250 GTL
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tyang
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Post by tyang »

Hi John,

Let's see if I get this right. The Ferrari ignition is wired positive lead from the ignition switch through the coil to the points and through the resistors to ground. The points are wired in series so when one opens, the field in the coil collapses. With two sets of points on three lobes, they are spaced to alternately fire the six cylinders on that bank.

Does this make sense?

Tom
'63 330 America #5053
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JAV
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Post by JAV »

Tom,

that would make perfect sense except that in the manual that I have, it shows both points connected to ground with the ouputs wired in parralel to the coil neg post. It does not show the points in series.

I suppose the manual could be wrong and that might be my confusion since the with a parralel wiring approach, the only way ground would be interupted is if BOTH points open.

I seem to recall Detomaso/Pantera using a dual point arrangment that did just that, dual points with an open overlap (to increase dwell and coild energy_... I wasn't sure if ours were the same because it doesn't look like the cam would provide that type of movement?
John Viveiros
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Post by tyang »

Hi John,

Which manual do you have? Some later Ferrari distributors for U.S. emissions had 6 lobes and two sets of points so one set could be used for idle and ease of starting. Once the throttle was pushed past idle, the second set of points would come into play. Does your manual describe this wiring?

Tom
'63 330 America #5053
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JAV
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Post by JAV »

Tom,

the manual I have is a photo copied compilation of what appears to be someones notes and it's mostly geared to the 330 but has quite a bit of 250 info in it as well. It has some diagrams and the distributer does show only 3 lobes, with dual points... and parralel wiring (which I suspect is wrong).

There isn't a functional description of how the system works, just directions for setting up the points and timeing. I got the manual from John Vardanian (thanks again John!) and it has really helped with understanding the ignition and carburetion. I think that one schemetic may be wrong though.
John Viveiros
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Post by 8339 »

Hi Guys, I just had to put a V-12 distributor on my Sun Machine to answer the question for myself. The points to the best of my knowledge are wired in parallel, each set of points grounds through the base with a wire off each set of points to the single post on the distributor. Each set of points operates three cylinders, Columbo was pretty smart to do this. the points are working half as hard, less point bouce, less heat generated for each set of points and the points can be phased. Also in the old days if one set of points crapped out they would only be down three cylinders. Ferrari always wanted to finish a race. I personally think these distributors are a work of art, ball bearings at the top and bottom, contact points with multiple leaf springs. the design is not far removed for the first 1.5 GP motor.
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JAV
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Post by JAV »

8339,

thanks for the info and if true, then I'm confused again.

If both points are grounded, in parralel, and both outputs are connected to the coil negative lead (I presume you meant "coil" not "distributer"?)... then how the does the coil fire? In this arrangement, how would the coils negative connection be interupted to colapse the feild? :cry:
John Viveiros
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Post by 8339 »

Hi John, I just had to go back and look again, using a VOM, both sets of points overlap each other, so when one set is about to close the other is opening. The points are closed more than they are open. Timing is everything, the clearance of the points is the difference of working and not working. Dwell is the amount of time or degrees the points are closed. Both points have to be phased to give a 60 deg. firing of the spark per rotation of the distrbutor. You made me really think about this!!

Richard
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JAV
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Post by JAV »

Thanks Richard!

If the points overlap "open" then that makes sense.
John Viveiros
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Post by whturner »

JAV wrote:Tom,

I seem to recall Detomaso/Pantera using a dual point arrangment that did just that, dual points with an open overlap (to increase dwell and coild energy_... I wasn't sure if ours were the same because it doesn't look like the cam would provide that type of movement?
Thanks Richard, for clarifying the issue.

That is the same same procedure used for many years (think pre-WWII), in both production cars and aftermarket. It would be more important in a high rev. Ferrari engine than the low RPM Packard, Ford V-8 and others. But they were 6 Volt ignition systems, so perhaps the same dwell increase for high rpm was deemed desireable even then.

But I am still having a bit of trouble visualizing the sequenceing which lets one set of points fire 3 plugs, and the other set fire, as has been described. the other 3 plugs. Or is that statement wong/misleading?

Cheers
Warren
330 GT Series II sn 10069
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JAV
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Post by JAV »

Warren - I think I can answer that one.

The points don't fire the plugs at all, all they do is cause a coil discarge. The distributer rotor controls which plug gets the energy like a rotary switch. Since each distributer is feeding 6 plugs , there needs to be 6 coil discharges thus with 2 sets of points and 3 distributer cam lobes, you get 6 coil firings per revolution of the distibuter.

The confusing part is the parralel / series arrangement of the points. Each set of points can fail individually and cause all the plugs to stop firing, or they can fail such that only 3 plugs fire.

For example- in a parralel system, if one set of points fails in the closed position (always supplying ground to the coil), the coil will never fire, and thus no plug will ever fire either.

If one point set fails in the open position, the other set of points, by virtue of it's parralel wiring, will still cause 3 coil firings per revolution as it makes and breaks the coil negative connection - thus only 3 plugs will get the energy through the rotor.

It's exactly opposite on a series system. When one set of points fails in the open position, no plugs will fire and visa versa.

Does that make sense?
John Viveiros
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Post by whturner »

Hi John:

I did use "fire" in a casual sense, like a rifle fires by pulling the trigger. But I was wondering about the ststement that one set "fires" 3 plugs, and the other "fires" the other 3. I couldn't see how that could be true, but I have seen that several times.

Of course there were in the past dual point sets coupled to distributor caps and rotors that could achieve that within one distributor body,(complex to say the least) but the Ferrari system is none of those. The ignition is the same as my '47 Ford. (Maybe Ferrari copied it)

Cheers
Warren
330 GT Series II sn 10069
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JAV
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Post by JAV »

Warren,

I hope my explanation didn't come off as condescending... as that wasn't my intent. I appologize if came off that way.

But I think I understand your point (pardon the pun)- that in each setup (series or parallel) "both" sets of breaker points play a part in firing all 6 plugs - if the system is working correctly. And either set can disable all 6 plugs in certain failure modes. In a literal sense though, each points "break event" does control the firing of just 3 plugs.
John Viveiros
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Post by whturner »

Hi John:

No apology needed - it is often appropriate to start a discription from the basics, especially when the audience has an uncertain background. I often start a presentation with such a "review".

In thinking about the Ferrari ignition, it appears to me that a 3 lobe distributor cam, coupled with the appropriate rotation speed and firing order, would have to be analysed in more detail than the straughtforward 6 lobe cam and single point setup for other 6 cylinder engines.

Or am I making it too complicated and confusing myself?


Cheers
Warren
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JAV
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Post by JAV »

No,

I agree completely- I too find it more difficult to understand, hence my original question. Even now that I understand it's a parallel system, I'm still wondering if adjusting one set of points will change the timeing on the second since it's the overlap that counts?
John Viveiros
1964 250 GTL
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