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2 breaker 1 coil distributor


Guest nmh

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Greetings,

I have a 1929 Auburn 8-120 sport sedan. It has 2 breakers and 1 coil.

It has 4 lobes on the distributor, and according to what I've read, the points

Are connected in a parallel circuit and each set of breaker points fires

4 cylinders. This has me baffled. If the points are parallel, each set

Must open before the plugs can fire, so how can each set fire 4 cylinders?

Can someone enlighten me? I need an explanation of how this works.

Thanks

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I think the answer you're looking for is that they alternate.

It can't work that way. Points ground the coil until they open, collapsing the magnetic field and causing a spark. If the two sets of coils are connected in parallel, one is always grounded, so no spark. Dual point distributors used on high performance cars in the 1960s used the two points with overlapping opening and closing so that the dwell period could be maintained at higher RPMs. That doesn't sound like what's going on with the OP's distributor.

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I was thinking of something different, though I still don't exactly understand based on the o.p.'s wording.

From Dyke's, this should be the explanation for his system (which I believe is Delco):

Delco Interrupter with Two Contact-Breakers Connected in Parallel, Using One Coil

In Figs. 4,5,6, and 6A, note that the closed-circuit type interrupters have two interrupters or contact breakers operated by one cam.

One spark plug per cylinder is used and also one coil, but two contact points connected in parallel, both of which open at one time. The primary ignition current which could otherwise flow through only one set of points is divided between two sets, and the resultant wear upon the points is less and an additional factor of safety is provided. The Marmon, Cadillac, and Cole use this principal.

_________________________________________

So, I'm guessing his distributor cam is turning at crankshaft speed, but given the Dyke's explanation I don't understand how each set of points can be divided amongst sets of cylinders.

nmh, where did you read that each breaker fires a separate set of cylinders?

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I looked into the wiring in my National Service Data and, indeed there is a 4 lobe cam in the distributor for the 8 cylinders. The actual distributor wiring is not shown, but they MUST be in series, not parallel. Otherwise, if parallel, the coil primary would always be grounded, since the points alternate. If this is the case, the need for two point sets amounts to smoke and mirrors, unless, I too am in the dark.

Frank

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I looked into the wiring in my National Service Data and, indeed there is a 4 lobe cam in the distributor for the 8 cylinders. The actual distributor wiring is not shown, but they MUST be in series, not parallel. Otherwise, if parallel, the coil primary would always be grounded, since the points alternate. If this is the case, the need for two point sets amounts to smoke and mirrors, unless, I too am in the dark.

Frank

Yes, that's correct. The points must be in series, not parallel, and clocked 45 degrees off from one another. That's the only way two sets of points with one coil can fire eight cylinders with a four lobe cam in the distributor.

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Exactly right - same system that Packard, Cadillac and others used on 8-cylinder cars in the early to mid-thirties; dual points in series, 4-lobed distributor cam on an 8-cylinder engine. In 33/34 Packard also used dual coils and a double-ended (alternate-firing) rotor, but setup is the same. Any good service book of the era, Chiltons, AEA, etc. will have instructions but perhaps this will be of help:

PackardClub.org • View topic - Synchronizing NorthEast dual points

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The delco-remy service manual states: the 2 contact arms form parallel circuits for the ignition current and the circuit thru the coil is not broken until both sets of contacts are open.

One half of the cylinders are fired by each set of points and on the 8 cylinder distributor with 4 lobe cam, the points must open 45 degrees apart. If the points do not open at this interval, half of the cylinders will have different timing from the other half. "

This parallel circuit makes no sense since both breakers have to be open at the same time to pull the secondary circuit in and if they are parallel how can half the cylinders be fired by one set, not both. But the above is straight from the service manual.this relates back to my original question. Early 8 cylinder engine manufacturers wanted to avoid chatter of the points, or bouncing at high speeds, so by using 2 sets of points the odds of both bouncing at once were less and enough dwell would be achieved. Then, the parallel circuit makes sense but not the statement "one half the cylinders are fired by each set of points"

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