How Tight Should a Helicoil Be?

[Toestr]

I'm looking to helicoil some aluminum head bolt threads because the bolts were over torqued (bolts were stretched, threads don't feel too bad, but 'slopier' when not fully tightened compared to other threads on the block). These aren't the only head fasteners on the block; the main sealing fasteners are larger nuts on studs which have a torque spec roughly twice these bolts.

I bought a kit from Harbor Freight and tried a couple coils in a piece of scrap. When I partially thread bolts into the test coils it feels about as loose as the 'bad' threads on the block. I drilled one hole slightly undersized to make sure it wasn't the hole size and it was the same way.

I understand that the coils are supposed to be sprung outward against the tapped material to keep them in place; so is this normal? Or are the Chinese tap and coils to blame?

[Tarsun2]

probably just harbor freight to answer your question. But if its mission critical, there are better options out there.

[Ecapnation]

Nutserts all day....

Helicoils are just ok but ultimately can pull out and fail. Depends on application too....a helicoil doesn't seal well with pressure.

[1snowridr]

I prefer retaping the hole with a larger thread when possible.

[cockerpunk]

loosness of the threads in the aluminum is scary cause it probably means they have been deformed and thus are weaker and maybe can't hold the bolt stretching torque.

loosness in the helicoil i wouldnt worry about less. helicoils are stronger threads that the original, and they are being held in place with a larger (stronger) thread that the original.

when you break off the helicoil, the slightly deformed bit at the full depth should hold it in place.