I received a box of coils (12-16) a few weeks ago and I would like to test them to see if any of them are rebuild able. What two terminals are to be tested for continuity?
Thanks in advance
Test the secondary windings by checking the ohms value between the two side terminals, points insulated.
Should be about 3300 ohms. Ford coils will usually give better results than other manufacturers.
If the secondaries are in spec, it should be good for rebuilding, barring internal terminal wiring separation.
Check this thread out.
Be_Zero_Be in Leesburg, VA
Good additional info !
Here is a diagram of a Ford coil internal wiring.
The wiring on other coils is always electrically the same, but can be physically different.
An open secondary winding is by far the most common fault. If the winding is defective the coil is usually no economically repairable. Remember they made 75,000,000 Model T coils and finding another is easy.
Other internal wiring faults can easily be repaired.
You also need to carefully inspect the coil box terminals. They are two piece construction and can be open between the parts because of corrosion. Flowing a bit of solder over the terminal will usually correct this problem.
Ron the Coilman
Don't forget internal arcing will make a coil not rebuildable and and it will not show up till the coil is powered up and the spark tested.
Your correct and you will find that latent fault in one out of every 75-100 coils during rebuilding.
You detect this fault during the rebuilding process, when the old capacitor is removed and before the new capacitor has been installed, using a 1000volt a Megger connected across the two windings.
Ron the Coilman
If a person does not have a 1000volt Megger you just install the new cap without soldering and test the coil on the HCCT before soldering, potting and installing the lid.
I also learned the hard way to do a final test of operation in the coil tester BEFORE repotting with tar.
Ok, so i just tested all my spare coils. i got results from the side terminals anywhere from 3.44 to 2.88 and a couple tested open.
soooo, the more variance you have is there more of a variation between cylinder timing?
and is there other things i need to check for the ones that test open? i suppose the connection to the side terminals.
Matthew said:"soooo, the more variance you have is there more of a variation between cylinder timing?"
Not necessarily. Inter-cylinder variance is a function of "ramp to fire" time, which several things can affect, most significantly, point tension.
I am eager to test the ECCT as I think it will take a lot of the guess work out of the inter-cylinder timing issue.
Tom, Im very interested in how you tuned your ignition system for the Montana 500.
You mentioned something about impedence and consistent Q values, could you elaborate on this?
Also any other info you have on coil selection would be great,
The Montana 500 guys from Spokane get angry with me because they think I talk too much. They like to keep some of their secrets under their hat as they are worried about Garrett Green and the Californian bunch. Even though I'm sure Garrett has thought of everything we've done already. As such, I will be a little cagey.
Have you read the Montana 500 newsletter articles that I referenced in some of these threads, namely the "Bucket Analogy" and the "Coil Comparison" articles? If you have any specific questions about something that I wrote that was not clear, feel free to ask them.
Don't get too hung up about impedance and Q-factor. It isn't that big of deal when driving at "normal" speeds, say up to 45 MPH. But, if you are interested in high speed, there is a reason we Montana 500 drivers want a high Q-factor. This is a clue to one thing we do with our coils. Cryptic, I know, but ask yourself why we would want coils with a high Q-factor. If you can figure this out you are on your way to a major speed secret. I will say no more on this at this time.
We all run Anderson style timers which we make sure are well timed. For that I have a huge degree wheel that I attach to the radiator and use the starting crank as an indicator.
Ok now im friggin stoked. im going to go look up those articles. this is exciting.
Here are links:
cool! i read both of them. some of the electrical testing is above my head, but i understand the majority.
hopefully my buddy has enough body parts to put together a T to specs. im thinkin the Montana 500 is my new goal!
I think John Regan makes a tester for that purpose. It goes beep if they are good.
Don't forget the "P" factor. It does seem to help when they look "pretty".
I am with Erich on the check before putting the tar back!
A good quality Chinese 1000 volt Megger costs $60 on Ebay.
In my view, if you rebuild any more than a few coils it is a great trouble shooting tool that will save you time.
Remember my favorite saying; "if you need a tool and don't buy it, soon you will find out you paid for it and don't have it".
But, I am always mindful of the favorite saying of my Colorado Model T Friend; "some Model T folks wouldn't spend five dollars to get cured of cancer" Grin
Ron the Coilman