COILs

[ChuckLebeda]

I have taken the coil box of a '21 coupe. Car has not been started. Is there any way to check each coil to see if it is good? Thanks. Chuck

[Humblej]

No, not without the proper equipment.

[ChuckLebeda]

Humblej: That is what I thought. So I will put them back in and see if it starts. Thanks, Chuck.

[Ruxstel24]

If you have a battery hooked up, you can get an idea by hand cranking each cylinder up and checking the corresponding coil. Once you install the box.

[BE_ZERO_BE]

Chuck,
Is there anyone near you that has a coil tester?
If the coils have been "At Rest" for a long time it would be best to simply send them off to a coil specialist to have them rebuilt.
Once this is done they will last a lifetime.

[ChuckLebeda]

Ruckstel24: I can not get the coil box lid off when it is installed under the dash. So I will have to reinstall and reconnect all wires to the plugs and timer. The coils are old wooden Ford inscripted coils; but previous owner had installed all new points,etc. So don't know if they have ever been rebuilt? Previous owner has passed. So I will install and try as you say.

Be_Zero_Be: I had Ron the Coilman rebuild me a set many years ago. Like you said, last a lifetime. These coils may have been rebuilt, not sure? Someone installed all new points on them though???? So for now will try the cheap way out; reinstall and try to start.

Thanks, Chuck

[Mark Gregush]

This might help

[ChuckLebeda]

Mark: Thanks for the diagram. Will see what tomorrow brings. Not supposed to get much above zero tomorrow, so lots of time to work before Spring. Chuck

[MKossor]

Nice coil information but I take issue with a very important specification.

Cushion Spring Gap: 0.010"-0.012" (recommended) By who and based on what data?

Here is data I took on cushion spring travel during development of the Electronically Cranked Coil Tester (ECCT) using a specially modified set of coil points with adjustable cushion spring travel.

Note that there is no significant change in coil firing time or firing current once the cushion spring travel reaches 0.006" That means the point contacts have opened after 0.006" travel even if there is more available travel before the cushion spring hits the limit rivet stop. In other words, the vibrator spring contact separates from the cushion spring contact all by itself after 0.006" of cushion spring travel without the help or benefit of the limit rivet stop.

This is a critical detail many do not understand the consequence. Coil points with excess cushion spring travel (More than the 0.005" Ford recommended) point contacts separate without the help or benefit of the limit rivet stop often do so relatively slowly, negating the purpose of the capacitor (condenser) promoting the formation of an arc. Coil point arcing is undesirable for several reasons. 1. Arcing causes premature wear of the electrical contacts. 2. The arc continues primary coil current flow but at decreasing value which weakens the eventual spark resulting in poor combustion. 3. The arc delays how long it takes for the primary coil current to cease to produce spark. This spark delay is also variable based on the coil point physical characteristics (point gap, cushion spring tension and vibrator spring tension) which produces ignition timing variation that diminishes engine power and introduces engine vibration. Now, it is entirely possible to adjust these 3 variables with the balance necessary for the coil to fire spark with equal and consistent firing time with excessive cushion spring travel. It just may take a while to find the right balance and may drift off that balance much easier over time. I have personally adjusted coils with 0.020" cushion spring travel for equal and consistent firing time in 5 minutes where as others with similar cushion spring travel required over 1 hour!

Ford knew what he was doing by specifying cushion spring travel of 0.005". The primary coil current is already of sufficient amplitude to guarantee a good hot spark with sufficient energy to insure combustion after 0.005" travel of coil point contacts closed. Both point contacts are traveling with considerable momentum after 0.005" cushion spring travel. The cushion spring contact stops abruptly when the cushion spring hits the limit rivet permitting the vibrator spring contact to continue moving, away from the cushion spring contact VERY Quickly. The capacitor (condenser) permits primary coil current to continue flowing for a short period of time (millionths of a second) but that is long enough for the point contacts to move physically apart from one another with the cushion spring contact abruptly stopped by the limit rivet. Abrupt physical separation afforded by the limit rivet and brief continuation of primary coil current by the 0.47uF capacitor is key to preventing electrons from jumping the point gap and forming an arc. This also hastens the collapse of the magnetic field once the primary coil current ceases to flow through the capacitor. This results in a higher secondary voltage to be produced creating conditions necessary for the spark plug to generate spark.

Coil points with excessive cushion spring travel are common due to lax controls during manufacture. It is possible to reduce cushion spring travel by crimping the limit rivet in a controlled way. Mike Vaughn published a method of reducing cushion spring travel in the Jan-Feb 2018 issue of the Vintage Ford magazine. Be careful not to over crimp the limit rivet or the points will be rendered useless.

The cushion spring tension must still be adjusted for proper tension even with 0.005" of travel. Too little cushion spring tension OR too much cushion spring tension will result in the vibrator spring contact pulling away from the cushion spring contact pre-maturely then quickly closing again to produce the dreaded double spark; a dreaded condition because it produces a weak spark earlier then desired followed by a second weak spark occurring later than desired relative to piston position. Poor engine performance results from insufficient spark energy delivered at the wrong time.

Folks who adjust their coils for equal and consistent Firing TIME (better than 90%) know the marked difference it makes in engine performance. There is a huge difference between a Model T engine that "Runs" and one that Runs Well.