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Helicoil came out with the bolt: why, and how to fix it
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#helicoil came out#thread insert came out with bolt#remove helicoil#coil insert repair#stripped thread repair#thread insert extraction

Helicoil came out with the bolt: why, and how to fix it

Amir Khan

A coil insert that comes out with the bolt was not held by its hole. The usual causes are a hole tapped with the wrong or a worn tap, a hole drilled too big, a thread not cut deep enough, or an insert left sitting too high. Don't screw the old coil back in. Take it out, check the tapped hole with a new insert, and fit a new one. Only if the special thread itself is damaged do you need a bigger repair.

This follows Stripped thread: thread chaser, coil insert or bigger bolt?, which covers choosing the repair and fitting it. This piece is for when that repair has failed.

Why did the insert come out?

An insert stays put because it is wound into a thread cut for it and springs out against that thread's flanks. If that thread is wrong, the insert grips the bolt harder than it grips the hole, and the bolt takes it with it. Böllhoff, which makes HELICOIL, sets four conditions in its kit catalogue. Each one matches a way the repair fails:

  • Only the special tap. Böllhoff says to use "only the special HELICOIL taps". A standard tap in the next size up cuts the wrong thread. The coil has nothing to lock into.
  • The right drill, held straight. Böllhoff gives drill sizes "only for orientation" and says to tap with the hole centred and vertical. A drill that wanders or wobbles opens the hole up, so the tap cuts shallow threads.
  • A fully cut thread. The insert must be "seated in a fully cut thread". In a blind hole, the first threads a tap cuts are tapered, not full. If the hole was not drilled and tapped deep enough, the bottom coils sit on a weak thread.
  • At least a quarter turn below the surface. An insert left proud or flush has its top coil on the hole's lead-in, where it can catch on the bolt and unwind.

How do you get a half-out insert out of the hole?

If the insert came away cleanly on the bolt, unwind it from the bolt and discard it. Refit with a new insert, not the one that failed.

If it is half out and binding, use an extraction tool. Böllhoff lists HELICOIL extracting tools by size, from M2 up to M36. The usual tool sets a blade into the top coil. Turn it anticlockwise, and pull up gently as the coil loosens. Keep the tool centred so the blade does not touch the tapped thread. Then clean the shavings out of the hole.

Can you put a new insert in the same hole?

Usually, yes. First run the kit's tap through again by hand to clear the thread and take it to full depth. Then wind in a new insert with the installation tool. It should take steady resistance all the way in. Stop when the last coil is a quarter to a half turn below the top face, and break off the tang with the kit's break-off tool.

Before you refit the part, test it with the bolt. Run the bolt in by hand, tighten it to the original torque, and back it out again. The coil should stay where it is.

TOPTUL JLAZ stainless steel coil inserts
TOPTUL JLAZ stainless coil inserts: refills for the JGEW kits, so you can refit without buying a whole kit.

The new insert will not hold if it spins freely, goes in with almost no resistance or comes out with the bolt again. That means the special thread in the hole is the problem: it is oversize, cracked or off-centre. Two options are left:

  • An insert inside an insert. Böllhoff's Twinsert kits are made for holes that are "over-sized", cracked or off-centre. A larger insert goes into a larger hole, and a standard insert goes inside it. The bolt stays the original size. Böllhoff makes them for metric coarse threads from M2 to M16.
  • Re-drill for a larger insert and bolt. This only works where the part has wall to spare and the mating part can take the larger bolt. The torque figure and socket size change with it, as the stripped-thread guide explains.

What should you check before you start again?

Check that the kit matches the bolt exactly: thread size, pitch and insert length. For example, the TOPTUL JGEW2403 kit for M8x1.25 holds 12 mm (1.5D) inserts, an 8.3 mm HSS drill, an HSS tap, an installation tool and a tang break-off tool. If the first repair was made with a mixed set of parts, or with a tap from another kit, start again with one matched kit.

Find the TOPTUL JLAZ replacement coil inserts and the JGEW coil-insert repair kits by thread size in the Vesprr Tools catalogue.

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