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benjo · 8 Apr 2009 at 22:19

How about a brief description of what a helicoil is?

GeForce · 8 Apr 2009 at 22:23

helicoils - Stainless or steel threads inserted into aluminum threaded holes to strengthen the connection on the inside for attaching a screw.

I didn't know that either.

Also, why two threads?

SGCWill · 8 Apr 2009 at 22:42

Good job; Could have used your help on my 250 hornet though. :mad:

Cylinder 1 decided it had enough of the plug and so decided to eject it at 18Krpm.

Thank god it didn't have enough force to turn me into a eunuch.

All fixed and working fine.....for now.

I have concluded that 2 stroke engines are much easier to work with.

Dogbreath · 9 Apr 2009 at 00:25

Kermit said:
In essence, with a helicoil you drill out the hole to oversize (a 6.3mm drill bit was supplied), then retap this with a tap (I guess 6.3mm again), then screw in the helicoil which fit the newly tapped 6.3mm perfectly but its inside diameter is M6 like the original thread was

Thread inserts use non-standard diameters, a drill size of 6.3mm would be used for an external thread diameter of around M7.3 for a 1mm pitch.

Handy hint for metric tap drill sizes: subtract the thread pitch from the major diameter to get the drill size required, e.g. is tapping an M6x1 thread, you'd need to drill a 5mm hole.

Fido McNasty · 9 Apr 2009 at 00:38

Good job that man. Satisfying isn't it

Dogbreath · 9 Apr 2009 at 02:15

Kermit said:
wrong (at least in the case of my kit)

My drill bit says 6.3mm on it so I'll take it as read that its 6.3mm and iirc the tap also says 6.3mm.

Maybe there's some helicoil kits (for coarser threads?) where the difference between the whole to be drilled and the tap is greater?

I think you may be confused on drill/tap sizing. If your tap really does show a size of 6.3 then it's showing the drill size it's to be used with rather than thread size. Whilst taps normally show the thread size, STI (Steel Threaded Insert) taps do not use standard metric thread sizes so displaying drill size is probably more logical.

If you think about it, you wouldn't get very far trying to make a 6.3mm major diameter thread into a 6.3mm diameter hole. The tap would just be a snug fit in the hole, it wouldn't be able to actually cut any threads.