Just yesterday I had to insert some Helicoils in my Sanglas bike. I use to take the camera with me and document everything I do on my bikes, so I thought some of you could be interested because the subject pops up often.
In one of the engine covers, sometimes in its previous life, the threads were damaged. Somebody, either not knowing what a helicoil was or being unable to find it, simply threaded a bigger bolt -not even using a tap-. I could have lived with that, but being kind of perfectionist, I decided to give Helicoil a try.
You need a set first. Each sets comes complete with inserts, drill, tap, insertion tool and blunt chisel. Each set is specific for one measure: M6, M8 etc, and there comes different insert lenghts. You can buy spare inserts. What you need to buy if you don't have it already is the tool to turn the tap -sorry I don't know the name-. This set costed 46 euro.
With the drill provided you clean the stripped thread and prepare the hole for the tap. Use compressed air to clean the shavings out. Then, WD40 into tap and hole and tap new threads. I should have to check it out, but I think the dimensions of the tap are not standard, but specific for the inserts. That is, if you lose or break one you will probably have to buy it from the Helicoil company or buy a new set.
If you have never tapped a hole, it is a matter of making sure it starts perpendicular, and as you feel the tap "biting" the metal, turn a little backwards every now and then to let the tap put the material into the recesses. It is easier to do than to explain, but to remember easily, something in the line of "two steps forward and one step back". How much should you introduce the tap? As much as the lenght of the insert, or the hole.
You need to know the threaded lenght you need. If the inserts are short you can "stack" them. Insert one to the bottom, and then insert another one in front of it. Once the second one bottoms out with the first, you need to break the ends of both -later-
Before inserting the Helicoil it is recommended again to blow the hole to clean out the shavings. Again, WD40 in hole and insert is recommended. You need the special tool to introduce the helicoil, as easy as inserting a bolt. You will need the "turn tool", the same that you used for the tap. In the picture you can see the end of the helicoil protruding out of the hole. It is just for the picture; you have to introduce the helicoil below surface level. The end of the insert wil "bite" or "punch" into the metal, avoiding it going out when removing the bolt. We are almost done....
Finally, with the blunt chisel and a hammer, a light blow will break the opposite end of the insert. The insert is machined so the end will break clean and the end of the helicoil will also "bite" the metal, therefore the insert will remain there without going backwards or forward. You have to remove the broken piece of wire. In my case, in one of them it jumped out and it hit me hard in the hand; wear googles. In the others it stayed inside. I didn't have tweezers so I just blew air inside until I couldn't see it. If there is remaining hole at the bottom you can live it there, but if the helicoil is the same lenght than the hole you will need to remove it or it will damage the bolt and/or the insert. A thin stick or cotton bud smeared with grease can work too. If you have used two inserts stacked, it is just a matter of breaking both ends. As you can imagine, if the hole is too long you can use two inserts, one at the top and another at the bottom, without nothing in between. The helicoil is harder than the aluminium threads, so chances are you will be good enough with that.
And that's it! A new threaded hole for the original M6 bolts....
