HCCT coil adjusting
I am sure this has been covered before, but I could not find anything. As I have understood it in the past, to adjust coils on an HCCT, one must adjust it to draw 1.3 amps and have 16 sparks around the ring with no double sparks. I notice some brands of HCCT have 16 evenly spaced marks on the spark ring, some do not. I believe I have read on the forum that it does not matter where the sparks are located, as long as there are no double sparks and the amp draw is 1.3 amps.
I do have questions, and I am not trying to stir controversy, but I have also read that some believe the ECCT to be slightly superior to the HCCT because it adjusts a coil to a dwell/time to fire, not an amp draw to fire, so that it is not the amp draw- thus spark strength- that is first importance, but the spark timing that is first important, and by adjusting for time, all four will spark at the same time relative to crank TDC allowing for smoother operation.
When I read the “Instructions for using the Ford Agents’ Coil Unit and Magneto Test Stand” as found on Fun Projects website, there it does not specify the 1.3 amps as critical, it states 1.2 to 1.4 amps, but it does also specify the spark should be located at the marks or points on the spark ring, not just randomly located. My question is, and sorry if this has been covered before and I missed it, but should the spark location be critical? It seems to me that by making the spark location critical as instructed to do in this old manual, (and not the amp draw) one is doing exactly what the ECCT is doing, it is adjusting the coil to a dwell to fire time, so all four coils fire at the same time relative to TDC. And of course, if this is true, then the pointer on the HCCT must be properly timed to the magneto position. With the pointer timed properly, it seems one could see where the spark is on a properly marked spark ring very precisely, even down to being off by one degree, which I believe is the resolution of the ECCT.
And so, if I am interpreting all this correctly, isn’t the HCCT, used as in this old manual, indicating that Ford did clearly understand that coils should be adjusted using the dwell to fire method, just as the ECCT does? And, for what it is worth, the HCCT would adjust about as accurately for dwell to fire as the ECCT, (although still much heavier to move around)?
The system designed by the Ford team was not as complex as the modern critics state.
The system operates on alternating current from an alternator, the magneto, to operate an induction coil.
The coil will operate on AC or DC voltage. But better with AC.
Depending on the source, the author and the authority at the moment, an operating buzzing coil is going to ignite the air fuel mixture and the engine will produce power.
The HCCT and the buzz box, with meter, will be sufficient to adjust the coils to allow the motor to run.
Anything else is over thinking, and taking the enjoyment out of the driving and Model T experience.
Actually, no instruments are necessary to adjust coils to allow the motor to run according to those who post they do so by ear.
There is, however, a huge difference between a motor that "runs" and a motor that runs optimally. Those who have never experienced a Model T engine with accurate and consistent ignition timing are understandably skeptical of the remarkable difference it can make. Hopefully others will share their driving experience with coils adjusted for equal dwell time to fire.
The challenge with the HCCT spark gap as an indicator of spark timing is the number of variables involved. The spark gap can vary between the pointer and marked ring locations. That's the idea behind the rotating spark gap, its gap never changes but then becomes a moving reference. The oxidation on the spark ring also can cause delayed or missing sparks to occur. I believe that's why coil current was used as the indirect approximation of coil dwell time to fire spark. Assuming all coils are electrically identical and firing consistently (periodically without intermittent point arcing) setting them for the same, steady, average coil current is a reasonable indication all coils have the same dwell time to fire spark. It should be noted that this adjustment is done at abnormally slow engine speed of 60-120RPM with abnormally low magneto output voltage of 3V-6V but still resulted in marked improvement in engine performance compared with coils adjusted by ear or buzz box which made it the preferred method of coil adjustment for ~100 years.
I think you are spot on. Some of the old HCCT's didn't have the marks on them (mine doesn't). As an experiment, I placed masking tape on mine and inked it where the spark occurred. Unless the gaps are all over the place, the sparks occur from one coil to the next at the same spot once adjusted. I have seen claims that they can be off by 6 degrees. I do not believe it and here is why. Using an 8" drum and dividing the circumference by 360 it shows each degree is .070 inches from the previous. This means the sparks would have to be 7/16 of an inch away from where the previous coil sparked. I have played with too many coils to believe that actually happens. Start fooling with the gap adjustment and see if you can even make the spark move 1/8th.
If individual coils are marking at the same point, there will be no timing error. In the case of a double spark , one will be slightly to one side of the reference and the other will be about 3/16 from that one. That is about 2 1/2 degree error.
Coils are current devices. They create an electromagnet to open the points. Ford understood it enough to know the strength of the magnetic field being the same on all four would produce like results. The timing errors are created by a misunderstanding of the cushion spring and the function of the limit rivet. If the rivet isn't set to the correct depth or if the cushion spring isn't set to the balanced spot, that is where the error is introduced.
My experience has been if you have four coils set on an HCCT that all throw single sparks while cranked at low speed, they tend to spark in the exact same spot and will produce a car that runs very smooth.
I used to use a buzz box, and got my car to run very well with it - but the important thing was that I did not have a magneto, so multiple sparking was not such a problem.
Having analysed how the firing actually worked, it occurred to me that there is a definite time to fire once the 6V is applied to the coil via the timer. And, this time to fire is dependent on coil setting. This is when I started experimenting, measuring the firing time with an oscilloscope.
Once the coils were adjusted to fire equally; 3.5ms with 6V, there was a noticeable increase in smoothness and low end pulling power.
I then learned of the ECCT and how it used the same principles. So, I was curious to try the ECCT. It worked so well I bought one.
The buzz box will tell you if the coil is bad, if you see no sparks at all.
The buzz box cannot tell you if the coil has random mis-fires, or has double sparks, or how good it is.
If the HCCT has spark ring notches, the 16 sparks might not line up with the notches or half way between them either.
With the Allen Original or Repro HCCT, it is easy to just loosen the big lock nut and shift the flywheel slightly to position the spark alignment with the notches or half way between them.
The fundamental operation of Model T coils and the magneto powered ignition is relatively simple and easy to understand. Achieving the best engine performance possible, however, requires far greater detail that is much less apparent, frequently misunderstood and therefore, often under appreciated.
Consider 3 coils with dwell times to fire of 0.001s, 0.002s and 0.003s driven by the same magneto voltage and test them in the venerable HCCT with the same 8" spark ring as Gary's. How far apart are the sparks? The answer is: it all depends upon the engine RPM. At brisk HCCT speed (120RPM) they are just a fraction of a degree apart (+/-0.72 degrees). However, at normal engine speed (1000 RPM) they would be a whopping +/-6 degrees apart. Take a look at the table below to appreciate the importance of coil dwell time to fire variation with engine speed. At high to top end (1500-2000RPM) these coils will have a huge +/-9 to +/- 12 degree timing error! Yet they fire only One Thousand of a second apart.
Now let’s translate this timing error to spark position change. At brisk HCCT speed (120RPM) sparks will be just +/- 0.050” apart on an 8” spark ring under ideal conditions (uniform spark gap, free from oxidation, constant rotational velocity, etc.). However if you could crank the HCCT at mid to top end engine speeds, the sparks would be a very noticeable +/-0.419” to 0.838” apart.
Its true coils are basically current operated devices but details of operation that dictate engine performance are vastly more complicated. The magneto output is AC with amplitude and frequency proportional to engine RPM. The faster the engine turns, the higher the magneto output voltage and the higher the frequency of that output voltage. The coil dwell time to fire spark is inversely proportional to magneto output voltage. The higher the voltage output, the faster the coil current reaches the level necessary to pull open the points to fire spark. At the same time, however, the higher magneto output frequency causes an increasing phase shift (time delay) between magneto output voltage and coil current and since voltage output is directly associated with crank shaft position and coil current level is directly associated with when the coil fires spark, the spark timing relative to crank shaft position also varies with engine RPM in a self compensating way. Anyone who tried shining a timing light on a Model T crank while operating on magneto will notice ignition timing remains essentially constant over a wide range of engine RPM. This is also why the previous linear extrapolation of predicted spark timing will deviate from prediction. Adjusting coils for equal dwell time to fire spark using a fast voltage pulse consistently produces excellent engine performance in my experience.
In the end, the best way to adjust Model T coils is the method you choose, enjoy and produces engine performance that you enjoy driving.
I appreciate all the responses, but apparently, I am not asking my question clearly, as the responses are not answering what I thought I was asking. I am not asking about various methods of adjusting, why they should be adjusted, how much difference adjustment makes, whether by ear or buzz box is good enough. Let me try again.
My question is (without the background stuff I included above)-
What is the proper way to use an HCCT:
1. Adjust for 1.3 amps and 16 single sparks on the spark ring, location not important (I believe this is the method I read about on the forum.)
2. Adjust for somewhere between 1.2 to 1.4 amps and the location is important, sparks being at the 16 marks on some HCCT model rings. (this is the method I believe the old Ford instructions outline.)
Once this is determined, I may follow up with more questions.
And try to use same cranking speed for each coil. Doing so eliminates 90% or more of the peripheral issues raised above.
I set all 4 coils to fire at 1.3 amps with single spark around the ring. My Allen does not have index marks and no volt meter. I see getting the timer centered to the cam as important in setting the dwell. Isn't dwell the ramp up time to fire when the points open?
If the cushion spring is set for single spark, the gap is correct for both it and points and draw is 1.3 wouldn't it follow that if all the magnets are the same strength and the wave is occurring at the same point and strength, that the dwell would be self set. ? I am thinking that the important numbers in Mike's chart are in the under 1500RPM (which would be over 35MPH with stock rear end)range were most people operate their T's.
Ok self disclosure, I am not an electronics wizz.
Jeff, (or anyone else) what is the logic that #1 is better than the way Ford suggested?
I use your #2 question.
I have been into Model T's since 1964 and played on them from the 1950era. My family T's, 1912,1916,1918,1918TT know how to go which surprises members with other "better" quality veteran cars.
In the late 50s I was an Indentured Electrical Apprentice and got involved in Model T coils in the auto electrical department at my works. These things were a head ache.
When we, my wife and I, bought our 1923 T, my headache got worse so you have to think more. Never heard of a HCCT and the ECCT and I assume Mike K were not even thought of back then.
I ended up using a 1923 T engine block, crank, coil and flywheel. MY 16 spark points were the aluminium magnet bobbins. you would be surprised what that tought me about setting coils. Current range up to 1.5A,Bridge to core gap varies. What I set for was a vertical spark of 1/4inchon each bobbin. a 2nd spark would show off at an angle. you could also pick up the advance and retard action of a coil. I Picked up KRW HCCT in the 90s and don't use the pick up ring but opting to use my bobbins as the spark earthing point.
I have an allen hcct that has no index marks, the sparks float in the air, therefore, i pay no attention to where the sparks occure as long as they are not double sparks.
#1 is essentially what the Ford HCCT instruction manual recommends. If you read it carefully, you’ll note that it does not specify an exact location for the sparks on the ring.
When I use one of my HCCTs with a fixed spark ring, the sparks always seem to be in the same location, equidistant around the ring, but not exactly on the center of the notches.
Eric, I do not read it as you do.
Per the manual- “…if the vibrator on the coil unit is properly adjusted and the unit in good condition the hand on the meter will register between 1.2 and 1.4. Also one good spark will jump from the ring to the pointer at each of the sixteen points on the ring.”
I read "at each of the sixteen points on the ring" to be just that- at the points, not randomly???
Mike, questions on your comments above. First, in your opinion, is there an ideal dwell time? 0.001, 0.002, 0.003 seconds, or something else?
Also, you mention the spark pointer/ring effects timing. I thought the timing occurs when the vibrator points open, largely independent of spark plug gap or plug condition in the chamber.
The dwell time to fire spark depends upon the applied coil voltage amplitude and rise time. The nominal dwell time to fire spark operating on 12V battery is 0.002 seconds in my experience.
Please note that the dwell time to fire in my previous example (0.001, 0.002 and 0.003 seconds) was a rather extreme case to convey the physical position of the spark depends upon how fast the HCCT crank is turning. Such large variations in dwell time to fire spark would be apparent the coil current difference when tested on the HCCT. For example, I adjusted a coil to fire spark at 0.0015s, 0.002s and 0.0025s when tested with a fast rising 12V pulse; this is half the dwell time to fire spark variation in by previous example. I then tested the coil on an Allen HCCT. The average coil current readings were 1.1A, 1.3A and 1.7A. I did not mean to imply the HCCT is not capable of detecting such large variations in coil dwell time to fire spark. Just that the physical locations of the spark is not a good indicator of differences in dwell time to fire spark when observed at abnormally slow (120RPM) crank/engine speeds.
Coil dwell time to fire spark is mainly dependent upon the time the coil current takes to ramp up to a level sufficient for the corresponding magnetic field to pull the vibrator spring contact away from the cushion spring contact. There are several other factors which determine when the arc actually occurs but with much less significance such as the spark gap distance, ambient pressure, ambient humidity, ambient temperature and electrode oxidation. In the extreme case, I have experienced missing sparks when testing a known good coil on an HCCT with rotating spark needle to a fixed ring. I found that reliable and consistent sparking was restored at all 16 points when I cleaned the spark needle and ring with scouring pad to remove any oxidization. I was surprised by this observation and surmised that some of these variables could influence when and where the spark actually occurs on the spark ring but do not have measured data to determine to what extent. HCCT average coil current is the best indication of variations in dwell time to fire spark in my experience.
One of the most difficult challenges I found using coil current as an indirect approximation of coil dwell time to fire spark was point arcing. Double sparking is very apparent on the HCCT when the cushion spring has in sufficient tension to follow the vibrator spring contact until the cushion spring hits the limit rivet and the contacts open prematurely. However, the cushion spring may still lack sufficient tension to follow the vibrator spring contact all the way to the limit rivet, especially when the limit rivet travel greatly exceeds Ford's recommended 0.005". Point arcing occurs when the vibrator spring contact slowly pulls away from the moving cushion spring contact before the cushion spring hits the limit rivet; stopping its travel. An electrical arc develops which does not cease coil current flow in the primary winding. Coil current continues flowing, increasing the dwell time for fire spark (i.e. retarding the spark). A second (double) spark does NOT occur because of the time delay; the magneto voltage is now decreasing in amplitude and the resulting current is insufficient to open the point contacts again at this time. Point arcing can occur on an intermittent basis which causes ignition timing variation and degrades engine performance. The skilled HCCT user must develop an eye for judging excessive point arcing and/or irregular coil current fluctuations to realize additional cushion spring tension is necessary. There is always some point arcing that occurs when the point contacts finally break contact so judging how much arcing or current fluctuation is too much is a bit of an art which I found difficult to master reliably.
Mike, thank you for your response.
I can understand why dirt on the spark ring would prevent a spark, but I have trouble understanding how it would effect spark timing to any degree. I have never previously heard that spark plug gap, dirt, etc., would effect spark timing on any other engines. But if that is what you observed???
Next, you say on 12V DC, 0.002 seconds in nominal. Is that what the ECCT tests for, or does it test for something else?
Lastly, in your view, back to my original question, do you believe Ford's instructions of spark location being important, was to adjust to a dwell to fire rather than current to fire and that that would be preferred?
Tom, I read it as Mike's response to having dirt or a little bit of corrosion insulating the area where the spark should occur on the tester spark ring this just has reference to tester ( hcct ) not how the coil would perform in the engine. It is important to keep the tester clean and contacts bright and shiny
Tom, the other variables have a much less significance on when the spark occurs as I stated previously. This mainly depends on the amplitude of the coil secondary voltage necessary to produce the arc. The secondary voltage builds up very rapidly (microseconds) compared with the coil dwell time to fire spark (milliseconds) so any variation should be insignificant. I don't have data on the time delay effects of the oxidized high voltage contacts other than the observation that it can suppress the spark from occurring all together.
Yes, 0.002s is the ECCT nominal dwell time to fire.
I think the Ford instructions specify checking for 16 individual sparks occurring rather than 16 individual sparks occurring at specific physical locations. I think the physical location the spark arcs to can vary due to some of the variables I mentioned so think that is not a good indication of dwell time to fire. The consensus is; setting all 4 coils for the same average current at the mid rang point (1.3A) provides the best indications all 4 coils will fire spark with the same dwell time. Assuming, of course, all 4 coils share identical electrical characteristics.
I have read much discussion on the double spark issue, and to eliminate double sparking, the cushion spring adjustment is typically the problem. I also understand that the goal is 16 good single sparks, but could not find a discussion when one does not have them. So what is the cause of missing sparks on the HCCT tester, and how does one get the missing sparks back?
Tom, Missing sparks on an HCCT can be caused by three things in my experience:
1. Defective coil - A coil operated without a proper spark gap (1/4" maximum gap) can arc internal to the coil; producing a carbon trail which promotes internal arcing before the spark can jump the spark plug gap under compression within the cylinder.
2. Oxidized spark needle or spark ring can cause missing sparks. Clean spark needle and spark ring with scotch bright to remove oxidation and repeat test.
3. Arcing between spark ring and HCCT housing. Inspect insulation between spark ring and housing. I found this happening on mine by having someone operate the HCCT dark and viewing the HCCT from different angles. Mine was arcing intermittently between the spark ring and the Jewell meter housing. The insulator was not doing its job so had to replace it.
Hope the cause is not number 1 because a coil arcing internally is typically not recoverable.
Thank you, so if the missing spark is a coil problem, not a tester problem, it most likely is a bad coil, not improper adjustment.
While might not be true for all HCCT's, another point could be the pickup ring behind the drum. My Allen has some flex in the plate mounting so when I see missing sparks I think that might be the issue. The one on mine is brass so it could also have dirty spots. It needs to be clean also. The Allen has a single spark jump point so is easy to clean that one spot. In case you wonder, unlike the types that the spark jumps from the point to the inside of a drum or ring, the Allen has a spark gap on the outside. As the handle is turned there are the normal 16 sparks, but they are on the outside of the center drum.