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Critic
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Re: Hard to see how this is possible
Critic   7/16/2015 10:17:20 AM
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@ErnieGG:

I am a firm believer in graphical documents like schematics and wiring diagrams that make clear how things are connected for this very reason.  Words are inadequate when it comes to describing how things are interconnected, and are not an efficient way to convey the information.  I don't think that my ways of saying things are any more correct than the ways that most other people say them; there is no right or wrong when it comes to languages, nor is there any right or wrong language.  The best we can do is to take steps to verify that we are on the same page, and I think you and I are on that page.

I have also seen distributors with secondary terminals that point sideways, on cars that had limited hood clearance.  This Volvo didn't have limited clearance above the distributor, though.

Secondary wires are usually well insulated, so even if they do touch something like a dipstick, there is no short.  It is not at all unusual for secondary wires to touch grounded metal parts and still perform as intended.  Low voltage terminals are often exposed because there is no hazard and no expectation or corona or arcing.

ErnieGG
User Rank
Iron
Re: Hard to see how this is possible
ErnieGG   7/16/2015 9:41:24 AM
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As I said, I was wrong about the fuse, and yes, wrong on two counts.

However, you're focusing on one detail rather than the overall idea. You said

"You remember incorrectly.  The points, which make and break the primary circuit of the ignition coil, were typically located in the distributor.  One contact of the points was grounded at the distributor; the points broke the ground-side contact to the coil."

I had said

"If I remember my old cars properly, the INPUT to the distributor is 12 volts from the primary of the ignition coil. How could repeated contact with the dipstick not result in a fuse blowing?"

So you're saying that the points broke the ground-side contact to the coil (which is at 12 volts when the contacts are open), while I said the input to the distributor is 12 volts from the coil (which falls to ground when the contacts close. Both of those are true so it's not possible for ONE of us to be correct on these points. Those statements are

"different points of view of the same thing."

I already said I was wrong about the fuse. And you're right about the high voltage wire being on the top of the distributor, though I have the nagging sense that I've seen one come in from the side and make a 90 degree turn down into the distributor. Let me rephrase, turn downward at some angle less than 90 degrees to the ground, lest someone point out that distributors don't always sit with their shafts normal to the ground.

Critic
User Rank
Platinum
Re: Hard to see how this is possible
Critic   7/16/2015 9:25:49 AM
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@ErnieGG:

If your "approach and mine are different points of view of the same thing," then why would you think that shorting a terminal that is shorted by the points during normal operation would blow a fuse?  Grounding the distributor side of the coil primary does not generally cause an over-current condition.

How do we know that the dipstick didn't short the secondary (high-voltage) terminal?  The article says that the dipstick shorted a terminal on the side of the distributor.  The high-voltage terminal is on the top of the distributor.

Here is a picture that shows the positions of the dipstick and distributor:  www.californiaclassix.com/Bernard/PV544-6.html

ErnieGG
User Rank
Iron
Re: Hard to see how this is possible
ErnieGG   7/16/2015 2:49:38 AM
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You and I are talking about the same thing. I say the points get 12 volts through the ignition coil. When the points are open, the voltage at the high side of the points is indeed twelve volts (yes, I know, nominal!). 

You say the points ground the ignition coil. Yep, they sure do. They complete the circuit that energizes the coil so that it can provide the spark when the field collapses.

I can understand that there are two approaches to describing this. What I don't understand is your not seeing that your approach and mine are different points of view of the same thing.

I was wrong about a fuse in the circuit. But surely the dipstick running into and making contact with the lead from the ignition coil would interfere with operation. If the dipstick contacted the lead at any time near the points' release, a spark would be inhibited and/or would fire randomly later.

The original poster may have intended to say that the dipstick shunted high voltage to ground, reducing the spark. High voltage is also input to the distributor. 

One point I was making was that he was not explicit as to which "input to the distributor" he was talking about.

Critic
User Rank
Platinum
Re: Hard to see how this is possible
Critic   7/15/2015 10:28:49 AM
NO RATINGS
 

@ErnieGG:

You remember incorrectly.  The points, which make and break the primary circuit of the ignition coil, were typically located in the distributor.  One contact of the points was grounded at the distributor; the points broke the ground-side contact to the coil.  When the ignition switch was on, battery voltage was connected to the other primary terminal of the coil.  The subject short caused by the dipstick would have been on the ground side of the coil primary; at the points terminal. The short would not have caused excessive current to flow because shorting that side of the coil periodically was normal.  The short didn't allow contact to be broken when it was supposed to be, though, which killed the ignition at times.

Many cars (including this Volvo) from this era did not have fuses in the ignition circuit, so even if the battery side of the coil primary was shorted, it wouldn't have blown a fuse.  It might have caused some wiring damage.  Some later cars had fusible links (wires that were designed to melt, basically) in the ignition circuit, but these might not have been damaged by an intermittent short on the battery side, if there were one.

Later cars also had ballast resistors in the primary circuit.  The ballast resistor would limit the current to increase the life span of the points (and coil and battery if the ignition is left on when the car is parked).  The ballast resistor was typically bypassed during cranking for a hotter spark initially.

ErnieGG
User Rank
Iron
Re: Hard to see how this is possible
ErnieGG   7/14/2015 9:17:58 PM
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It truly is hard to see how this is possible!

If I remember my old cars properly, the INPUT to the distributor is 12 volts from the primary of the ignition coil. How could repeated contact with the dipstick not result in a fuse blowing?

Now, if you mean the High Voltage input, which is the Ignition Coil output, I'd say right! And I'd say please give better descriptions!

Rob Spiegel
User Rank
Blogger
Re: Hard to see how this is possible
Rob Spiegel   9/9/2013 8:09:28 PM
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Yes, Ann, Berkeley was a bit more mature than the typical hippie ghetto -- although Telegraph had its hippie ghetto flashbacks. What I loved most about Berkeley during the early 70s was the music. Live music was everywhere, and it was all great. It was in the clubs, the coffeee houses, the bars, the theaters, even the parks.

Ann R. Thryft
User Rank
Blogger
Re: Hard to see how this is possible
Ann R. Thryft   9/6/2013 1:12:42 PM
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Wow, Rob, then you know what I mean. You must have seen a lot in Berkeley, too. It was still interesting in the 70s, after the Haight had imploded.

Rob Spiegel
User Rank
Blogger
Re: Hard to see how this is possible
Rob Spiegel   9/3/2013 11:45:28 AM
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Those were amazing times, Ann. I lived in Berkeley in the early1970s before I moved to New Mexico.

Ann R. Thryft
User Rank
Blogger
Re: Hard to see how this is possible
Ann R. Thryft   8/29/2013 2:21:04 PM
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I think I was mostly lucky because of who I hung out with. And yes, I was in San Francisco in the mid and late 60s as a teenager. Those were amazing times.



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