Length of spark3⁄8 inch1⁄2 inch1 inch2 inches
Size of bobbin ends21⁄8 × 11⁄421⁄2 × 5⁄163 × 3⁄84 × 23⁄4 × 3⁄8
Length of bobbin451⁄261⁄261⁄2
Length and diameter of core41⁄4 × 7⁄166 × 5⁄861⁄2 × 3⁄4
Size of base71⁄4 × 31⁄4 × 11⁄29 × 5 × 2141⁄2 × 6 × 13⁄412 × 71⁄2 × 31⁄4
Size of tinfoil sheets4 × 251⁄2 × 31⁄46 × 46 × 6
Number of tinfoil sheets36404060
Size of paper sheets5 × 361⁄2 × 41⁄49 × 5
Primary coilNo. 18No. 182 layers No. 16, silk covered.2 layers 14 B. W. G., silk covered.
Secondary coil3⁄4 lb. No. 401 lb. No. 4011⁄4 lbs. No. 3821⁄2 lbs. No. 36

TABLE OF SPARKING DISTANCES IN AIR.[13]

Volts.Distance.
(Inches.)
5000.225
10000.47
200001.00
300001.625
350002.00
450002.95
600004.65
700004.85
800007.1
1000009.6
13000012.95
15000015.00

Points Relating to Ignition Coils.—1. Most ignition induction coils or “spark coils” as they are called, have terminals marked “battery,” “ground,” etc., and to short circuit the timer for the purpose of testing the vibrator, it is only necessary to bridge with a screw driver from the “battery” binding post to the “ground” binding post.

2. In adjusting the vibrator of an ignition coil, the latter should not require over one-half ampere of current.

Fig. 147 to 161.—Wiring diagrams showing connections of some standard spark coils.
[Larger.]

3. A half turn of the adjusting screw on a coil will often increase the strength of the current four or five times the original amount, hence, the necessity of carefully adjusting the vibrator. When the adjustment is not properly made it causes, 1, short life of the battery, 2, burned contact points, and 3, poor running of the engine.

4. In adjusting a multi-unit coil, if any misfiring be noticed, hold down one vibrator after another until the faulty one is located, then screw in its contact screw very slightly.

5. The number of cells in the circuit should be proportioned to the design of the coil.