Stripping a bolt hole in an aluminum cylinder head can ruin the entire part. Heli-Coil inserts provide a reliable fix. The kit includes a drill bit, a special tap, and a coil of stainless steel wire. You drill out the damaged threads, tap the hole, and thread the coil inside. The coil acts as a new set of high-strength threads matching the original bolt size. It is a standard repair for spark plug holes, exhaust manifolds, and oil pan drain plugs. Always break off the installation tang at the bottom of the coil using a punch when finished.
Mechanic Glossary
Heli-Coil
A precision-formed wire thread repair insert used to restore stripped threads in engine blocks, oil pans, and aluminum parts.
Frequently Asked Questions
They are often stronger. The stainless steel coil distributes the load over a larger area of the aluminum housing.
Usually no. The coil is larger than the hole and stays in place through spring tension. You can use red threadlocker for permanent security.
Place a straight punch against the tang and strike it firmly with a hammer. The tang is notched and will snap off cleanly.
If used on a head bolt or coolant passage, fluid can weep through the coils. Apply thread sealant to the bolt threads during assembly to prevent leaks.