installing a Helicoil

[Donald]

Going to be installing a 5/16" Helicoil shortly. A couple of questions. The directions say to install the Helicoil so top is 1/4 of a turn below the top. The hole is about 3/4" deep and the Helicoil is about 1/2" long.

Here is the question:

Do I tap the hole all the way to the bottom and then just screw the Helicoil so its 1/4 turn below the top? Or tap the hole only deep enough so the Helicoil will bottom out at the end of the threading when the top is 1/4" turn from the top?

 

[Trav]

As long as the coil is 1/4 turn below the surface when installed it doesn’t matter one way or the other. I find it easier just to tap down to the bottom or through whichever is the case, the coil wont move.

 

[Chris142]

Loctite it too.that way it won't come out with your bolt next time you take it out.

 

[Ethan1]

It shouldn't matter if you tap the hole a mile deep because the helicoil insert will fit very snug. It will stay just exactly where you put it.

If you are installing it into aluminum, don't worry about threadlocker; galvanic corrosion will take care of that

 

[howie2092]

Thread depth does not matter, as long as the helicoil goes in to the correct depth.

Use red loctite on the helicoil, blue on the bolt. Don't ask me how I know that.

 

[Omahaug]

Yup rule of thumb is blue is usually removable with hand tools. Red is only removable with applied heat like a torch then they have some other weird colors like purple and green the latter I think is for low torque fasteners so it's like blue but weaker so you can use them with small bolts without snapping them.

If you do end up using Loctite make sure at least one of the metals from the two that sandwich it is "active", metals like stainless and plated metals are "inactive" and will require primer or you can buy primerless Loctite with primer already mixed in.

 

[Merkava_4]

Originally Posted By: Donald
The hole is about 3/4" deep and the Helicoil is about 1/2" long.


Why not tap the hole 3/4'' and install a Helicoil 3/4'' long?

 

[Trav]

It doesn’t matter if the threads are 2 inches deep as long as the threads are 1.5 times the bolt diameter deep maximum holding power is achieved.
Rounded off a 6mm bolt in a 10mm thread depth the 5/16 would be 1/2".
High strength bolts in aluminum and depending on on thread pitch 2-2.5 times is possibly more appropriate.
These application might include main bearing bolts and crankshaft nose bolts, etc but usually not in small diameter applications.

Originally Posted By: NoNameJoe
colors like purple and green the latter I think is for low torque fasteners


Green is for already assembled fasteners and purple is low strength. I use the purple and small diameter screws use on some watchbands for example.

 

[Donald]

I drilled the 21/64 hole but its not a clean hole, there are leftover threads. I assume someone tried to thread in a 3/8" bolt. The top few threads were 3/8" and the bottom few threads were 5/16".

I suppose I could go to a larger Helicoil, but I think I will try what I have (5/16").

 

[Donald]

Originally Posted By: Donald
I drilled the 21/64 hole but its not a clean hole, there are leftover threads. I assume someone tried to thread in a 3/8" bolt. The top few threads were 3/8" and the bottom few threads were 5/16".

I suppose I could go to a larger Helicoil, but I think I will try what I have (5/16").


Maybe Loctite would be a good idea here?

 

[Trav]

The red will hold it permanently but you run the risk of getting it on the bolt threads when you install it. I don't think you need it in this application. Just a little never seize on the bolt will do.