1. PARTS AND ASSEMBLY

A basic understanding of the parts and assembly will later help in the application and interpretation of the plug. (Cut-away plug below)

PARTS

A. Insulator – Aluminum oxide ceramic, must have good dielectric and mechanical strength, good thermal conductivity and resistive to heat shock

B. Center Wire – Must have good conductivity and be chemically and electrically erosion resistant (Approx. melt temp. of std nickel is 2500 degrees Fahrenheit)

C. Terminal Stud – Either solid post or removable terminal nut made from mild steel

D. Shell – Extruded or bar stock machined mild steel

E. Ground Wire – Typically made of same material as center wire

F. Washers (internal) material – Copper and steel

ASSEMBLY

A. Insulator - Molded dry under high pressure then kiln fired to vitrification at a temp. above the melting point of steel

B. Center Wire - Two pieces welded together, lower std. chrome nickel, upper iron (for strength in sealing process.) Center wire is dropped into the insulator then packed with sillment powder by a tamping process

C. Terminal Stud - The terminal stud has the cement applied then screwed on and tightened to a specific torque then allowed to dry or bake, providing a gas tight seal

D. Shell - After machining or extrusion the threads are rolled, then the ground wire is welded on and the unit is zinc or nickel-plated

F. Washer Material  - Racing plugs then get washers and the insulator unit is placed inside the shell, sillment is added with tamping if the shell is cold pressed or if it is to be hot locked no sillment is added (c types are hot locked; s and v types are cold pressed) finally the ground wire is trimmed and the gap is set

***NOTE: While our racing plugs all have a positive contact between the center wire and the terminal stud, (because of a slight indentation in the terminal stud), not all plugs will show continuity when tested with an ohm meter.  This is not a problem as the approx. .002" gap which the low voltage (approx. 1.5V) ohm meter cannot bridge, causes effectively no resistance to the minimum 5000V of an ignition system.  Some plugs have actually had a built in gap to combat a weak ignition/fouling problem.