Helicoil Shrinkage at Installation

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nm9stheham

nm9stheham

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Just as a matter of curiousity.....I was installing helicoils (in a new billet AL flywheel for the pressure plate bolts) and had to run one helicoil all the way through and out the back side, because I missed a burr in the threaded hole and the helicoil was not sitting in the hole right.

It was interesting to see just how much the helicoil shrunk from its original form. (I did have to turn it a bit harder than normal to get it past the burr so that may be part of this change.)

IMG_20200122_140309637.jpg
 
Gotcha.. it was more deformed than I would have expected. Thought it would spring back to the original form when it came out the back side but no. Tried starting it in again and there was nowhere near the original tension, so the material is permanently deforming.
 
One on the left has 14 threads. The one on the right has 16 threads . I believe you have two different coils. But I may be wrong.
 
You have a good eye OMM! I shoulda explained... the one on the right is the exact same part as the one on the left (both out of the same bag of 10), and started out looking exactly like the one on the left. The one on the left has not been installed.

The one on the right is the one that got installed and I subsequently turned all the way through the flywheel and out the back. The wire is deformed and pushed into a smaller diameter as it gets turned into the hole. The smaller diameter forces the helicoil wire to 'wrap' itself into more turns.

I never realized that the reduction in diameter would lengthen the helicoil so much. Or permanently deform the wire so much. Just thought it was interesting and worth sharing.

FWIW... this is for an 8mmx1.25 thread.... pretty much the same as a 5/16" coarse thread.
 
The larger diameter is to make a sort of interference fit so that when installed it will hold the the walls of the newly tapped hole. I learned many years ago thru trial and error on the fact that the hole it takes when you install the insert needs to be longer than the before length of the insert.
 
Might I add to Always be sure to use the correct Heli-Coil Tap and keep that Tap separated from the rest of your Standard Taps. I can't tell you how many guys I've seen grab a Heli-Coil Tap without paying close attention to it and use it to Tap a NON-Heli-Coil Thread = Scrap Part in my Industry.

Heli-Coil Taps will have an STI marking on the Tap = Special Thread Insert and they thread the hole oversize to receive the Thread Insert.
 
Oddly, I designed a trade show display for my work and had M4 spec'd Helical Inserts to be installed. Gave a part number and all. When I got them the shop didn't put them in because they forgot to add it to the quote. I said, "no prob, done this before.." For the life of me and a coworker who is also an experienced car guy could not get a helicoil in. I bought 3 different brands, spoke to the shop and could not get them to work and finally found a brand that would. Now I design in Keenserts (or equivalent name brand stake-able threaded insert) as most of them use a standard tap. I use them for tooling and trade show displays where they see lots of use by people who don't pay attention to much and they have held up great.
 
nm9stheham said:
You have a good eye OMM! I shoulda explained... the one on the right is the exact same part as the one on the left (both out of the same bag of 10), and started out looking exactly like the one on the left. The one on the left has not been installed.

The one on the right is the one that got installed and I subsequently turned all the way through the flywheel and out the back. The wire is deformed and pushed into a smaller diameter as it gets turned into the hole. The smaller diameter forces the helicoil wire to 'wrap' itself into more turns.

I never realized that the reduction in diameter would lengthen the helicoil so much. Or permanently deform the wire so much. Just thought it was interesting and worth sharing.

FWIW... this is for an 8mmx1.25 thread.... pretty much the same as a 5/16" coarse thread.
Click to expand...
I never noticed that myself . Now that you mentioned it I am going to watch for that . That is two complete coils but it does make sense.
 
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