Helicoil Info

I need to repair one of the threaded bosses where my shifter bolts to the transmission.  I ordered a 6mm x 1.0 pitch helicoil kit and it arrived the other day. The hole and corresponding bolt are about 1" deep/long. (sorry my metric fo is not good) The kit came with inserts about 3/8" long. Are these stackable or do I just repair the 1st 3/8" of the hole and that it all it needs. The inserts have a small tab that would seem to keep them from being useful stacked, does that make sense. What else can you tell me that o need to know. 

You stack them.  You insert the thread part using the tab, then break the tab off with a punch.  You did read the directions, right?

I use Helicoils on a regular basis in order to achieve stronger threads on aluminum castings. These are new parts. 

I never stacked them, I don't see how that would work as they will be very hard to line up end to end. 

I always like to see no less than 1.5x screw diameter of thread engagement when possible. With that being said, if you do not want to buy longer Helicoils (they sell them) you are probably OK with one. 

6mm =~.24”

.24” x 1.5 = .36”

If it was me I would use one.  

Remember to use the correct matching tap, they are matched to the insert.

In reply to Dr. Hess :

That sounds reasonable, I haven't opened the package yet and it does not appear there are any instructions.  It is in a small extruded plastic package but perhaps there is something inside sandwiched between the packaging. There is a tap and about 8 of the coils and a punch . I think I will contact the seller and see if they offer a kit with longer coils , as much as stacking them would seem to work I would have more confidence with 1 coils as opposed to hoping I can get them all inserted properly. I'm thinking I will need 3 or 4 to fill.the hole. Thanks for the ideas.

Just use one. 3/8" (.375") should be plenty of thread engagement for an M6 (.236"). I think trying to stack them will cause you frustration for little to no benefit. 

Also, that's probably the insert tool in the package, not a punch. It basically grabs the Helicoil by the tang to turn it into the hole. One the insert is in and below flush, take a regular old punch and knock the tang down.

As long as the Helicoil length is about 1 1/2 times the bolt diameter you will be fine.  They do come in different lengths. Max torque for a given bolt diameter can be achieved at about 1 1/2  times the bolt diameter without thread damage. 

You are adding a steel thread to an aluminum casting.  That simple act has probably doubled the holding strength of the fastener, so I wouldn't worry about the length. 

The tap you received should have the size of drill bit you need printed on the shank.  Don't fudge that on a 6mm.  If you were helicoiling a 12mm hole, there is some wiggle room, but the smaller you go, the more accurate you want to be. 

Thanks, between you guys and some local input I am going to use just one. I just need a little holding force and one coil should be fine. The kit tells me I need a 1/4" bit and the tool is the insert tool. With my newfound knowledge I am ready to attack it, should be hard to screw up.

Any thread engagement over 6 threads (course or fine) is essentially doing nothing. Really the first three are doing the work.

What I remember from the machinery handbook

Here's instructions with pictures: http://knowhow.napaonline.com/know-how-notes-how-to-install-a-helicoil-insert/