blue coil, ballast resistor, and crane 700

[Bad Dad]

Same symptom on the way home from work. Had a nice little break on the side of the road, and then off again problem free for the rest of the drive. The car runs like a champ with no stutter until it abruptly cuts out. 
 

I realized I do not have the black/white wire connected from the starter, it’s just the green. But that seems fine. The only issue I can see now is that the Crane XR700 is faulty. I read somewhere that part of the function of the distributor is to also tell the coil when to rest? It seems my coil isn’t resting at all, full blast at all times. Perhaps someone more knowledgeable can enlighten this part. 
 

Either way, the Hot Spark is on the way and I will have a mechanic install it and report back. 
 

Quote

Coils are energy transfer devices and the transformation mechanism is magnetism which doesn't involve heat so there's no intrinsic reason for a coil to get hot except.....

When the points close or the equivalent inside an electronic module the coil has 12 volts or so across it and current flows limited by the coil's resistance (well, technically, it's impedance) and the electrical energy is converted into magnetic energy stored in the soft iron core of the coil. At some point in time, the coil's core will be "full" of magnetism, ie saturated and any further current flow is just turned into heat until the points open, the current flow stops, the magnetic energy field collapses and the only place for it to go is via the high voltage generated by the coils secondary winding and off to the spark plug.

How long the points stay closed for is called the dwell angle and as in all design compromises the combination of how long the points stay closed, the number of cylinders to fire per revolution, the maximum RPM, the coil resistance and the mechanical constraints of a distributor all constrain the need to fully charge the coil and saturate it but minimise current flow that is just generating heat.

The most extreme situation is a stationary engine with the ignition on and in a position with the points closed (which is most likely) where the coil will just sit there sinking several amps and getting hot.

In a distributor with conventional points you are limited by how long the points can remain closed (and charging up the coil) by the fact that due to mechanical limitations it also takes time to open the points and you have to manage one open and one close cycle before the time comes to do it all again for the next cylinder which is not long in a 6 cylinder engine at 6000 RPM! If you have electronic points your open time is negligible and you can sink greater currents into the coil so there is more freedom to alter the dwell time to get a full spark at all RPM but to match that the designer may choose a coil with a lower resistance hence the rise of coils made specifically to get the most out of electronic ignition. That said, many electronic points modules or distributor replacements are designed to work with a standard "points" coil (2 to 3 ohms) for compatibility and originality and will do so very well and much better than mechanical points.
 

 

Edited August 14 by Bad Dad
Added quote

[John76]

47 minutes ago, Bad Dad said:

the function of the distributor is to also tell the coil when to rest?

Not exactly. When the points (or ignition module) is grounded, the coil is energized (building voltage).

When the points open (or the module tells it to stop charging) the coil fires volts to the plugs.

Further noodling on your issue.... does the XR-700 require +12 volts via the red wire?  What is the power requirement???

The 3-ohm coil gives the XR the return voltage through the yellow wire, so it should be a happy camper.

The 3-ohm coil therefore requires a 12-volt supply from the ignition switch. Resistor is not needed.

Check the resistance of your green wire from the hot side of fuse #12 to the coil (+).  If more than 1.9 ohms, you have a resistor wire.

Also, no need for the black/red or black/white wire from the starter. Not needed if you get +12v to the coil (+) through the green wire.

[Bad Dad]

Thank you @John76 I am learning a lot here, and hope my questions aren’t too elementary. I’m really puzzled by this issue. I almost want to see if relocating the coil would help, for airflow, but it would be strange to move it out of its 50 year home. 
 

I am puzzled by two things; PO claims he never had this issue, and the car runs like a rocket until it shuts down. Starts right up when cold. Everything seems in order. Whole rev band has plenty of juice. 
 

From what I can see in the Crane manual, 12V is the correct voltage (image attached) I can not see any other voltage mentioned. (And red wire straight to coil)
 

Tomorrow morning I will reinstall the original blue coil sans resistor and see if this changes anything. Last combination I haven’t tried. Since the car runs so well until the coil overheats, I feel the Crane unit is fine? However, perhaps it is the Crane unit overheating. (It never feels that hot to the touch) But if that was the case, I feel I would have some stutter. 

 

I think your advice on checking the green wire for resistance is my next step. 

 

One last thing. Since I picked up a new voltage regulator yesterday, I drove a little bit alternating between both today. The new one shows a more consistent and stable reading, just above 13V. So there’s that. And I have new plugs on the way. 

[John76]

Just to summarize:  

-  XR-700 needs +12v on the red wire.

-  XR-700 needs a 3-ohm coil.

-  There is +12v on the green wire from the ignition switch.

You have all the correct ingredients.

Connections:  Red wire to coil (+), Green wire to coil (+), electric choke wire to coil (+).

Yellow wire to coil (-), Black tach wire to coil (-).

 

I see no reason for the external resistor or a black/white bypass wire from the stater.

 

John

 

[Bad Dad]

I agree. But pardon my ignorance. Where does the coil draw negative current from? The only wire I see is the Crane feeding to the chassis. Thus, since the green positive and red from the crane are connected to the same place on the coil, won’t the Crane unit bypass the internal coil resistor, as the unit draws negative current from the chassis, and its red wire shares a connection with the green wire on the coil? Does the tach wire feed the coil with current?

 

This morning I replaced the plugs, and reinstalled the original blue coil with no resistor. The car took me to work in morning traffic without stalling. After the 40 minute drive both coil and crane unit felt hot, but the car ran fine. Rush hour heading home will be another test. Old spark plugs looked rough to say the least. 
 

I’m starting to realize why the resistor was put in place originally to the red Crane wire, as I feel the internal coil resistor doesn’t do much as the crane is connected to the chassis. But maybe I’m completely wrong here. 

Edited August 14 by Bad Dad

[John76]

1 hour ago, Bad Dad said:

Where does the coil draw negative current from?

The coil (-) is grounded by the distributor. Check to make sure the distributor is well grounded to the engine, and the engine is grounded to the battery (-).

The box (XR-700) needs +12v for the electronics and the trigger light. It has its own ground (black wire to chassis).

The external resistor is only needed if the coil resistance is less than the 3-ohms specified by Crane.

Example: If you have a 1-ohm coil, you need a 2-ohm external resistor. This will provide the right voltage/current on the yellow wire to the box.

The Bosch type K Blue coil has a 3-ohm internal primary resistor, so an external resistor is not needed. 

Double check the green wire to make sure you get battery voltage (+12v) when the ignition is on.

Perhaps the PO used the original Bosch type KW Black coil. This has a primary resistance of 2-ohms, and therefore required a 1-ohm externa resistor (or 1-ohm resistor wire). The red wire should have been attached to the side of the external resistor with the green wire from the ignition switch to maintain the +12v to the box.

Another thought...heat builds up when things are powered but the ground path is weak. Scrub all ground points and check the resistance of the wires all the way back to the battery (-). Should be as close to 0-ohms as you can get.

 

John

 

 

 

 

[Bad Dad]

This is very helpful, thanks again @John76 I will get hold of a voltmeter and measure everything. 

[visionaut]

30 minutes ago, John76 said:

heat builds up when things are powered but the ground path is weak. Scrub all ground points and check the resistance of the wires all the way back to the battery (-).

Heating can also possibly lead to “Low Voltage’ to the unit…

 

Perform the power and ground checks that John advised (both cold and hot).
If the voltage supplied is insufficient, the system may run for a period of time, and then shut down as the voltage drops further due to engine heat. The period may vary from minutes to hours depending on available voltage and wiring condition…

 

 

[Bad Dad]

update: New plugs made the car feel better and the new voltage regulator is giving me a better voltage reading (just north of 13 pretty constant) — but stranded again on the way from work. 
 

Blue coil is back, without resistor. I have been able to make some measurements. 
 

Green wire shows 0.05 ohm from fusebox to coil. 
 

Blue coil shows 3.7 when cold and 4.4(!) when hot and dead. Coil + to Crane Box ground shows 2 ohm. (For comparison the Pentronix coil reads 3.5 cold.)
 

Coil measures 8.5V while running. Coil to ground measures 13.5V. (I think I saw somewhere that the Crane box expects 9V)
 

Still not sure why the coil overheats. Car runs absolutely great until it abruptly cuts. 
 

I have the Hot Spark unit arriving this weekend, so I guess that is the next logical step. 

Edited August 15 by Bad Dad

[Bad Dad]

7 hours ago, John76 said:

The coil (-) is grounded by the distributor. Check to make sure the distributor is well grounded to the engine, and the engine is grounded to the battery (-).

Thinking further about this, I realized I have not seen a ground wire around the distributor. I came across this post related to it, but it describes a tiny internal wire in the original points assembly as far as I can see. Does anyone know whether the Crane assembly utilizes a similar approach? 
 

My only lead at this point. 

[John76]

The little internal wire on the stock distributor is the ground from the points plate to the engine block (through the distributor body).

The distributor is grounded by contact to the engine head through the gear and the clamping collar. 

Is the optical part of the Crane unit mounted to the points plate/advance mechanism? Looks like one of the three wires on the Molex plug is a ground wire.  Sorry, I'm not familiar with an optical trigger switch.

[Bad Dad]

Thank you. This is a good lead. Something tells me the coil doesn’t get a proper discharge, and lack of correct ground makes sense. I will dive in to the distributor in the morning. 
 

The crane manual mentions no ground, but I’ll look for anything that might seem like one. The middle wire could be it, I can’t see another reason why they’d be three of them. 
 

Thanks again for the leads here. I hope this thread can be of help to someone else in the future. 
 

 

[Bad Dad]

Nothing to see inside the distributor. The housing for the optical reader which has three wires going in, is all plastic, so I can’t see how this would ground anything. 
 

Engine stopped again. Made a new measurement. Coil resistance reads 4.6 ohm when hot. This tells me the Crane box doesn’t get enough power due to the increased resistance, when the coil heats up. 
 

(The new Petronix coil shut down in a similar fashion.)

Edited August 15 by Bad Dad

[jimk]

16 minutes ago, Bad Dad said:

Nothing to see inside the distributor. The housing for the optical reader which has three wires going in, is all plastic, so I can’t see how this would ground anything. 
 

Confusion crept into the distributor with a sensor.  The distributor does not have a grounding for this installation like a set of point contacts has.

The Optical pick up is only a sensor that reports to the Crane box which has any necessary grounding functions in it.

Edited August 15 by jimk

[Bad Dad]

Thank you. That eliminates that issue. 
 

Tonight I will redo do the green ignition wire to a proper 12gauge, and double check the Crabe box ground. Also have new spark plug wires on the way.