Serrated Spark Plug Thread Inserts
Heli-Coil serrated spark plug thread inserts are manufactured from 18-8 round stainless steel wire formed into a 60° diamond-shaped wire. This cold-worked wire, which has a tensile strength of 200,000 PSI, is wound into a helical coil with a driving tang and notch to remove the tang after the insert is screwed into the Heli-Coil tapped hole.
Retention Principles
In its free state, the insert is larger in diameter than the tapped hole. Once installed, the insert assumes the configuration of the tapped hole. The resultant outward spring-like action anchors the insert in place.
In addition, the spark plug insert has a serrated top coil which is offset and staked into the parent material. This process is recommended because of the high temperature and high performance requirements of spark plug ports. The Heli-Coil spark plug insert becomes an integral part of the cylinder head, providing high-strength threads which exceed in surface smoothness, hardness, and accuracy any threads tapped in any material.
Features and Benefits:
Permit easier spark plug removal because the possibility of corrosion is limited between the spark plug and the hard-drawn, smooth-surface stainless steel insert
Eliminate thread failure due to stripping, vibration, and fatigue
Extend thread life, even after repeated disassembly and reassembly
Greatly increase tapped thread strength under all operating conditions
Offer speed and economy in production salvage, providing greater-than-original thread strength
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