Ignition coil question

My son asked me and I didn't know the answer so I thought I'd pose it here. His bike has two ignition coils. The coils are not the same,
they are from different years of manufacture for different models of motorcycle. The timing is not the same for each cylinder, but should be the same. The coils have different resistance. My son was wondering if the difference in timing could be because one coil takes longer to build up enough voltage to cause the spark plug to spark. The coils are connected to the same control box. So I'm wondering if the voltage rise from two ignition coils could be that much different. Eric
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On 6/4/2014 8:15 PM, snipped-for-privacy@whidbey.com wrote:

Rl is the time constant. Likely the heat of the spark in one cylinder is needed to be more or less. Timing is critical and heat is also.
Martin
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snipped-for-privacy@whidbey.com wrote:

Yup, the coils need to have the same resistance. Your son is correct in the reason the timing is off.
--
Steve W.

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wrote:

When he says the timing is off, how is it being determined and how far off is the timing? If he is checking with a timing light on the secondary it might be BAREL:Y noticeable but the coils should be matched for other reasons. The build-up has nothing to do with timing - the spark happens when the magnetic feild collapses.(unless it is a capacitive discharge system -which is a totally different kettle of fish)
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On Wednesday, June 4, 2014 9:15:55 PM UTC-4, snipped-for-privacy@whidbey.com wrote: My son was wondering

I doubt it. Assuming this is a Kettering type of ignicion, the way it wor ks is that when the points are closed the current builds up in the coil. W hen the points open the magnetic field collapses which creates the high vol tage. The condenser across the points keeps the voltage from arcing at the points. You might swap the condensers and see if that changes things. If it does one of the condensers is bad.
Dan
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On Thu, 5 Jun 2014 04:05:12 -0700 (PDT), " snipped-for-privacy@krl.org"

Greetings All, I guess it's sort of a Kettering ignition. It doesn't use points though. Some type of inductive sensor tells a box when to make the coils spark. My son says he checked the timing with a timing light, which is why he knows when each coil is firing. Eric
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On Thu, 05 Jun 2014 09:11:06 -0700, snipped-for-privacy@whidbey.com wrote:

===================two types of ignitions
Kettering, where the coil "fires" when the points open. This is because the magnetic field in the coil collapses faster than it builds giving a "hotter" spark.
CD [capacter discharge] where a capacter discharges a higher surge of current/voltage with a faster rise time into the coil and it fires as the magnetic field builds up. If you have a "pointless" system, which is likely as you mention a module rather than points, it may well be a CD. Is this a computerized system where the advance is controlled by the module, and the sensor or points are just index location signals?
Coils are not that expensive, and he should use a matched set of used coils, if not new a new set.
here's a few places to start
http://www.motorcycle-superstore.com/motorcycle/Ignition%20Coil
http://ricksmotorsportelectrics.com/ignition-coils
http://www.jcwhitney.com/ignition-switches-and-coils/c51121j1s17.jcwx
--
Unka' George

"Gold is the money of kings,
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Dan sez:

We stopped using the term "condenser" in the 1960s <G>
ANYway... that's not all the capacitor does. It also controls the decay time of the field in the coil. And that depends upon the inductance of the coil -- the old "LC constant".
If the coils are noticably different in resistance, there's a really good chance they have pretty large differences in numbers of turns. That vastly affects the inductance of the coil.
If you wish to have both coils "fire" at the same time, you must have them inductively matched, and have the same capacitance across both sets of points (gotta be two, unless they were really dolts and paralleled two coils!)
Don't forget point gap. If there are two sets, then if they're not gapped exactly the same, the timing will change there, too.
Two new coils, two new capacitors, and two new sets of points are the best way to go. (might as well throw in plugs and HT wires, too...)
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in

That's on the assumption that both coils fire at the same time, but of course, if they don't then why are there two coils?
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

On my truck there are two independent sets of coils and plugs, on opposite sides of the engine. Except during starting they fire at the same times. I could add a Mag Drop switch.
-jsw
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And points, no? If only one set of points, it's a system destined to be unreliable. Even minor changes can affect the timing and voltage of the spark on one coil.
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

http://rockledge.home.comcast.net/~rockledge/RangerPictureGallery/DIS_EDIS.htm Look at figure 2. SPOUT is Spark Out, a logic signal which mimics the closing and opening times of points for the correct dwell and timing. The DIS module connects the (-) sides of the coils to ground like points, but electronically, and sends back something relevant to how the coil fired on IDM, Ignition Diagnostic Monitor. IDM was flaky on the module I replaced, giving a code though the engine ran well enough.
It's a computer controlled Kettering system, not CDI.
-jsw
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It still has two sets of "points", whether they be big MOSFETs or mechanical.
Lloyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

Actually it has four MOSFET switches, two for the right side coils and two for the left side coils, two plugs per cylinder. They replace the point contacts and the computer replaces the distributor point cam and the centrifugal and vacuum advance.
-jsw
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On Thu, 05 Jun 2014 17:46:28 -0500, "Lloyd E. Sponenburgh"

Electronic ignition - and computerized timing advance on the only 2 2 plug per cyl automotive/light truck engines I'm aware of.
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snipped-for-privacy@snyder.on.ca fired this volley in

A lot of them tried it in prototype, and should have stuck with it.
Anyone who's flown knows the difference in power that occurs when you switch to just one plug. ALL ATC'd aircraft (with piston engines) have dual ignition circuits. In aircraft, they're totally independent -- absolutely NO common components between the two systems, and often they are magneto systems to simplify the system, and ensure ignition in the absense of DC power in the aircraft.
Lloyd
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On Thu, 05 Jun 2014 20:54:38 -0500, "Lloyd E. Sponenburgh"

2 plug per cyl systems are a requirement on large bore engines to ensure all of the charge gets lit. On a small bore engine they are not required, and the ONLY reason for using them was emission compliance.
And as far as magnetos and reliability - there is a good reason they use two!!! Many "experimental" planes are using electronic ignition on at least one set, and there are STCs (Supplemental Type Certivicates) to allow installation of electronic ignitions (like lightspeed) on virtually ANY certified plane. With the electronic ignition systems you get more power and better fuel burn (lower fuel consumption) as well as generally easier starting, as well as better plug life, less fouling, - all advantages when an old "tractor engine" is all that's keeping your ass in the air.
Clare Snyder, Technical Director RAA (Recreational Aircraft Association) Canada
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On Thu, 5 Jun 2014 18:28:18 -0400, "Jim Wilkins"

Sounds like a Ford Ranger or a Nissan??
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On 2014-06-05, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

    If one fires too quickly after the other, there may not be sufficient time to build up the field for the second one.
    I know that my wife's Mazda RX-2 (Wankel engone) had two distributors, two coils, and two spark plugs per rotor -- one near the leading edge and one near the trailing edge. At a guess, this was to ensure more complete combustion.
    It made it fun trying to figure out how many cylinders for income tax purposes (when you got different mileage allowances depending on the number of cylinders. So to analyze it:
Actual number of cylinders:    0
Number of rotors:        2
Number of spark plugs:        4
Number of firing strokes per rev: 6    (three per rotor -- about                      equivalent to a V12).
    So -- how many cylinders could I claim? :-)
    Enjoy,         DoN.
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Depends on the *exact* wording of the law, but I bet that you can claim zero and cite the definition. For a parallel, look up the history of the mansard roof architecture of houses.
Joe Gwinn
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