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Thread Repair Helicoil Inserts Occasionally threads, both internal and external, are only partially stripped. These can be readily cleaned up using a die or tap. In cases where there are no threads a tap does little good. In these cases a stainless helical wire insert called a “Helicoil” can be used. Thermostat housings, cylinder heads, exhaust manifolds are a few of the places that Helicoils can be used. Helicoiling begins by drilling out the old threads with a specified drill bit for the insert size to be used. Drill straight is easier if you use a machinist square to serve as a guide. Each Helicoil requires a specific tap. (part of a kit) This will cut „oversize threads to fit the insert. Use cutting fluid, tapping fluid, WD- 40 or even a little oil when tapping aluminum to avoid galling and stripping the thread often leaving a weak thread. Clean out the shavings and hole completely. Using the insert tool, carefully wind the insert in to the threaded hole. Insert so that the Helicoil is below the surface and embedded into the recut threads. The tail is snapped off with a punch once the insert is in position. Answer the following questions: 1. What is a “Helicoil”. 2. What is the purpose of using a machinist square when drilling? 3. How are oversize threads made? 4. Why should you use cutting oil? 5. What two things will tell us if the Helicoil has been inserted correctly?
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