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Old 12-31-2020, 06:09 PM   #1
ericr
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Default (Yet Another) Electrical Question

I have read that the Model "A" engine always stops in one of two positions.

I always turn off the gas valve and let the engine die before shutting off the
ignition switch. I have noticed that if I fully retard the spark before turning the ignition off, the ammeter goes to zero but advancing the spark causes a negative reading on the ammeter....is that because the points are going from closed to open?

As a related question, what exactly happens if you let the engine die by lack of gas but forget to shut off the ignition switch? Does it burn out the condenser or
the coil or the points?
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Old 12-31-2020, 06:36 PM   #2
Oldgearz
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Default Re: (Yet Another) Electrical Question

I don't know about your ammeter part of this, but I do know that if you leave your ignition on and the points happen to be in the wrong position, you can cause the points to pit or actually fuse together.
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Old 12-31-2020, 07:02 PM   #3
Chuck Sea/Tac
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Default Re: (Yet Another) Electrical Question

It’s the opposite. The points are going from open to closed, which energizes the coil. If left like that, the coil will curl up and die from overheating.
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Old 12-31-2020, 07:28 PM   #4
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Itís the opposite. The points are going from open to closed, which energizes the coil. If left like that, the coil will curl up and die from overheating.

The battery will die as well.


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Old 12-31-2020, 10:10 PM   #5
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Default Re: (Yet Another) Electrical Question

Quote:
Originally Posted by ericr View Post
I have read that the Model "A" engine always stops in one of two positions.

I always turn off the gas valve and let the engine die before shutting off the
ignition switch. I have noticed that if I fully retard the spark before turning the ignition off, the ammeter goes to zero but advancing the spark causes a negative reading on the ammeter....is that because the points are going from closed to open?

As a related question, what exactly happens if you let the engine die by lack of gas but forget to shut off the ignition switch? Does it burn out the condenser or
the coil or the points?
ericr,

I forgot to shut off the ignition and my battery discharged. It was totally dead when I went back a week or so later. I had to buy a new battery and it started right up. I guess I was lucky because others have stated the coil and points can be damaged.

David Serrano
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Old 01-01-2021, 09:01 AM   #6
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ericr,

I forgot to shut off the ignition and my battery discharged. It was totally dead when I went back a week or so later. I had to buy a new battery and it started right up. I guess I was lucky because others have stated the coil and points can be damaged.

David Serrano

When my pop out ignition switch went bad a while back, in effect, it left my ignition on all the time. I happened to notice that the coil was very warm the next morning (prior to starting the car), and the battery voltage had dropped from 6.2 volts to around 1.8 volts. Apparently, it would take more than overnight to run down the battery totally. Fortunately, it didnít harm my coil or points either. Actually, that happened a couple nights in a row until I figured out the ignition switch was the culprit.

I could see accidentally leaving the ignition on for a week could kill a battery.


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Old 01-02-2021, 03:16 AM   #7
Ak Sourdough
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Default Re: (Yet Another) Electrical Question

To answer the non electrical part of the question, the engine will stop on the compression stroke of whichever piston is coming up when the flywheel no longer has enough inertia to overcome the resistance of compressing the air in the cylinder. The highest compression will be at the top of the cylinder, so it will very likely always stop near the same piston location.



If you mark the crank pulley every time the engine stops there will only be 2 marks on the pulley and it will look like it only stops in 2 places 180 degrees apart. Each mark will be the compression stroke for cylinders 1 and 4 or 2 and 3. Being a 4 stroke engine it takes 2 revolutions to make a complete firing cycle, 720 degrees. 1 and 4 will have the same mark, but fire 360 degrees apart, same with 2 and 3.
Clear as mud, huh?
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Old 01-02-2021, 08:39 AM   #8
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To answer the non electrical part of the question, the engine will stop on the compression stroke of whichever piston is coming up when the flywheel no longer has enough inertia to overcome the resistance of compressing the air in the cylinder. The highest compression will be at the top of the cylinder, so it will very likely always stop near the same piston location.



If you mark the crank pulley every time the engine stops there will only be 2 marks on the pulley and it will look like it only stops in 2 places 180 degrees apart. Each mark will be the compression stroke for cylinders 1 and 4 or 2 and 3. Being a 4 stroke engine it takes 2 revolutions to make a complete firing cycle, 720 degrees. 1 and 4 will have the same mark, but fire 360 degrees apart, same with 2 and 3.
Clear as mud, huh?
oh that is pretty clear.....but next, explain why the firing order is 1-2-4-3 instead of 1-2-3-4
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Old 01-02-2021, 09:03 AM   #9
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Default Re: (Yet Another) Electrical Question

Thatís not an electrical question

The middle pistons (2 and 3) rise and fall together. So 3 canít follow 2 in the firing order, it has to skip to 4.
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Old 01-02-2021, 09:07 AM   #10
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Sparky said this but here is my explanation.

Firing order: The two center pistons (2 and 3) go up together and two outside pistons (1 and 4) go up together. So when #1 is firing, #4 is up and switching from exhaust to intake stroke. And 360 degrees later the opposite is true. So if you look at the firing order as numbers on a circle rather than in line, you can see that #1 fires opposite #4 and #2 fires opposite #3, etc. The circle represents 720 degrees of engine rotation and the firing of the pistons are separated by 180 degrees. The #1 and #4 and the #2 and #3 are separated by 360 degrees. Hope this helps.
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Old 01-02-2021, 12:14 PM   #11
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Default Re: (Yet Another) Electrical Question

I always install quality battery cut off switches (Cole Hersey 2484 or the longer shank version) and get in the habit off shutting them off when a car is not running, and / or especially during /after maintenance, etc.
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Old 01-02-2021, 03:38 PM   #12
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I always install quality battery cut off switches (Cole Hersey 2484 or the longer shank version) and get in the habit off shutting them off when a car is not running, and / or especially during /after maintenance, etc.
I looked those up, how/where do you install them?
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