Wednesday night I went to a club members house and we tested my coils with the club's coil tester (I did not get the make or model). Each coil tested fine, except that each coil had a double spark, only when testing on high and they all showed in the same place, which was at the top mark (12 o'clock) on the dial. The info sheet said that was caused by a poor or weak bottom spring. Can anybody explain what a double spark is or means as far as the operation of the engine goes?
The basic idea is that one strong spark is better then two weak sparks.
If you only have one spark all the energy goes onto the one spark that fires the air/fuel mixture. If you have two sparks, each spark will be weaker and be less efficient for the first spark that fires the engine.
The anomaly is that Ford wrote in there HCCT manual that a double spark was okay and maybe preferred sometimes but today no one really knows the logic behind that idea.
It will affect inter-cylinder timing as you are sparking twice (with a time lag between first and second spark) with much weaker than normal sparks. Cylinder may fire at first or second spark (or not at all occasionally). This will vary the timing of firing between cylinders similarly as will coils set for different amperage (causing different time lag between contact and coil operation from coil to coil). It can also lead to incomplete combustion with resultant power loss as well.
At one time you could find the earliest Dykes manual claiming this was a benefit for easier starting and more complete combustion, but that opinion was abandoned, and I believe rightly so.
This is the one time where a modern device (Strobospark) is in my opinion, better than the original HCCT in that the Strobospark may be used to test at various voltages and the user can tune the coil to operate properly at what are essentially low, medium and high engine speeds (assuming driving on MAG). The HCCT is only at best effectiveness when cranked at CONSISTENT speed for all 4 coils when setting amperage and double sparking will not always show up at a particular speed of the flywheel, but will at another.
we were typing at the same time. You're fast!
for a good and clear explication you should contact Ron Patterson. He will be pleased to tell you how it works.
1> When the coils are installed in the coil box do they buzz and spark on battery?
2> When you hand crank or push the starter switch on battery, does the engine start?
2a> If you only have a magneto as designed by Huff and you hand crank the engine does the coil buzz and spark?
2b> Does the engine with magneto and coil only start and run?
3> When you switch (if your magneto works) to magneto, does the engine still run smoothly?
4> In my opinion then enjoy the car as it was manufactured, if you want "performance" then upgraded the ignition system install a proper magneto or a distributor.
My opinion is not necessary the same as other opinions.
How about a short, direct answer? If you have double sparks, you don't have the proper cushion spring tension on your upper coil point.
You can adjust cushion spring tension with one of John Regan's tools, or you can very carefully put a little twist in the bridge between the contact posts with a needle nose pliers. Of course, the old fashioned way to increase tension, is to give the upper coil point a light whack with the head of a screwdriver, right near the rivet.
George, in response to #4, the car was manufactured with properly adjusted coils. Don't settle for an underpowered engine due to improper maintenance of the simple ignition system. I can't tell you the number of people that have told me how amazed they are at how well their car runs after installing a properly rebuilt and adjusted set of coils
Eric is correct. Check to make certain the cushion spring is free to move.
Eric -- Same page.
Getting double sparks (or missing sparks) is what happens when coils are adjusted on a buzz box. They run OK on battery but not on magneto. This also what happens when someone sets coils 'by ear' or tries to adjust an otherwise good running coil to give a precise point clearance without putting them on a HCCT or Strobospark.
George is correct about Eric being correct.
Model T coil double sparking occurs when the downward tension of the cushion spring is not sufficient to allow the point contacts to remain in contact with each other until the cushion spring reaches the complete limit rivet travel range.
Double sparks are undesirable because the spark energy is dissipated when the coil starts to fire, stops and then starts again. The best result is when all the coils full energy is concentrated on one single spark.
Ron the Coilman
Ron, could you please expand on "is not sufficient to allow the contact points to remain in contact with each other until the cushion spring reaches the complete limit rivet travel range". What is meant by complete rivet travel range. Thanks....Jerry.
The upper point which is mounted to the cushion spring is supposed to stay in contact with the lower point during its downward travel until the cushion spring contacts the rivet. When it hits the rivet it comes to an abrupt halt and the lower point continues to move downward. This gives the points a good, quick, crisp opening, and a nice strong spark. When the cushion spring tension is not adjusted properly, the lower point will pull away from the upper point before it hits the rivet, but it is not a nice crisp break. The magnetic field still collapses and you get a weak spark, but the lower point immediately goes back up and makes contact with the upper one and starts another magnetic field which pulls the lower point down again giving you the second weak spark.
I think the Club owns a Strobo-spark...was that what you were using?
Also, this thread may help:
I slept at home last night!!
Hal the Coilman
Very good explanation.
Thank you to all who took the time to help me with your information. I wanted to check my coils because I keep having misses (but no backfires) when pulling a hill. It seems to me that a weak spark could be causing that problem.
PS: Dave so did I
I had a set of coils that tested good on a Strobo-spark but the car seemed to wheeze at high speed in use. I went through everything and no matter what I did that high-speed wheeze was still there.
One day Bob Jablonski just happened to stop over and at the time his HCCT was always in the back of his station wagon. Why not, let's go through them again I might have missed something before. They were old coils, some being original Ford. They were balanced for amp draw as good as it gets and then Bob did them again. Car still misbehaved at high speed (like driving in OD).
After scratching heads, (then) Big Bob decided to get that HCCT up to spinning at about as fast as humanly possible. Three came through with single spark flying colors...one was double sparking but only at high HCCT speed. We both shrugged and Bob asked if I had a spare coil. I have a dozen or so but they all needed rebuild...so we took a relatively new coil out of my other car and took the offending car for a ride. No bog down, full power when wanted, no high speed apparent 'skip'.
We put the newer coil back in the 15, and Bob offered to exchange my offending coil for one he just happened to have in his wagon which he knew was spot on. Agreed...no bog down, full pep...and it is now 2-3 years and that car is still the peppiest one in the stable.
I tried looking for consensus on why...never got an answer that made sense as most felt single spark at normal rotate speed on HCCT was a sign of 'good enough'. I don't know if Bob ever took that one apart or not.
Those coil points are only part of the problem.
The capacitors are almost always bad in those old coils.
Add to that the fact that many of the newer repro coils have a small .1 yfd capacitor instead of the proper .047 yfd capacitor in them.
Most Repros were made to work on 12 volts DC and were not planned for use with a Ford Magneto, so most do not work well and confuse people into thinking their T runs better on Battery, and it may very well run better, but not as good as it can get.
The StroboSpark measures the capacitor and checks it for leakage. It also verifies the capacitor can charge and discharge in an acceptable manner.
The HCCT can verify that the coil is not randomly misfiring the spark plug.
The HCCT can not verify that each coil will start firing at the same voltage/current level and when each piston is in the exact same position level.
Coils properly adjusted on the StroboSpark apparently kind of fine tune the required curent/voltage level required to produce each first spark.
The correct capacitor size is .47 yfd.
This comment was sent to me direct, from a competent party that prefers to remain anonymous, for posting: In the hands of a competent operator the HCCT can tell if the coil is consistently firing within 1-3 degrees of crankshaft rotation.
I will have to agree that when the piston is near the top, that 1 to 3 degrees does not change the piston level a significant amount.
GEORGE-Cherry Hill NJ:
Normal HCCT speed is about 60 rpm's. Spinning as we did back then was for shitz & giggles. Don't want forum members to believe "spinning" is normal.
Happy we got the '15's coils tuned. Remember when the depot hack acted up ? Suggested you use the tried & true coils from the '15 ...... and the hack's ignition problem disappeared. Yup, one bad coil will show it's ugly head & create doubts regarding all aspects of the ignition system..... timer, wires & contacts, plugs, coils, magneto output, generator & battery condition, coil box wood carbon tracks.
You can't go wrong in sending your coils to Ron Patterson for a complete rebuild that includes new capacitors.
It helps to know that the coils are good when trying to find a problem.
It was one of the first things I did when I got my dad's "beach wagon"
The problem with George's one coil..... bad secondary winding with internal arcing.... went to the recycler.
Interesting point, I rebuilt all 4 original coils for the vehicle months prior to George's purchase, seems that one coil was "replaced" before George took possession. That coil had the original condenser and later aftermarket point set.
Thanks again everyone. I was using the club's StroboSpark tester. Today Arthur came over and brought the tester with him so I could test my other coils. Here are my results: coil #1 cap value .5, cap leak .4, double spark on medium & high: coil #2 cap value & leak ok, amps all readings around 1.8: coil #3 cap value 1.55, cap leak .2, amps ok, but double spark on all 3 sittings: coil #4 cap value .95, cap leak ok, amps low 1.5, medium 1.6, high 1.6: coil #5 cap value .5 ok, cap leak 0 ok, amps low 1.55, medium 1.5, high 1.35 . I think it's time for me to have a talk with Ron Patterson.
I am leaving to attend a Model T tour in Argentina and will not return till October 3rd.
Ron the Coilman
We'll be sitting here waiting for pictures to start rolling in Ron.
I hope to see some good pics of non-Ford bodies on those Ts down there.
Problem solved, thanks to my good friend Dick Welch over in Bow, NH. I took all my coils over to Dick and he set them to the proper specs. Now Seabiscuit runs like the champ that he is. We drove down to the hardware and did not have one miss going down or coming back. The engine run cooler (my have been the weather) and went up the hills better. Thanks again Dick! I am going to see if I can talk Dick into doing a tune-up before next weekend club meet. We're going to the track in Loudon and race around, should be a lot of fun.
Hi Warren . I picked up rebuilt coils when I was in Baldwinville the other week and what a difference it made to our '23 sedan
They are the heart of the Beast. Ron Patterson did mine and they are great. Thanks Ron for getting them to Lang's in such a short time. Regards, John
Hello John, very happy to have met you, Ginny and friends. Yes what a difference good coils make in our pride and joys. I heard a great song the other day that I think you'll enjoy, "Bud the Spud" https://www.youtube.com/watch?v=TNEg65rlnu4