<VV> Two helicoils in line?

[Frank DuVal]

I commonly used two helicoils in line, as I had a source for shorter 
helicoils. I can now buy longer ones...

You tap the hole for the helicoils, and this sets the threads per inch 
for the helicoil. Now, when you screw in the second helicoil, it has to 
be synchronized to the first, as it is in the same tapped hole.

Once you install the second helicoil, you must remove the tang, as it 
will stop the bolt (stud, etc) at the shallow depth. I use a pin punch 
and hammer to break off that tang. Trap the loose tang, as you do not 
want it to be lost inside moving parts! Sometimes the tang is strong, 
and just bends, not good, as that lifts the helicoil off the sidewall of 
the hole. Best bet is to set the punch right against the tang at its 
attachment to the coil.  Do not apply the force of the punch to the 
loose end of the tang, mechanical advantage will help bend and not  
break off the tang. Breaking off the tang in a blind hole (valve cover 
bolts) is trickier, as you must use a magnet and a small diameter steel 
rod to get that tang out, or turn the object and let gravity do its job.

Frank DuVal

On 2/21/2012 11:40 PM, chuck mckinley wrote:
> The helicoil inserts
> are only about half the length of the threaded part of the stud, and I'm
> wondering if it's possible/smart/insane to drill and tap the hole far
> enough to twist in two helicoils, one behind the other, to give the stud
> that much more thread to grab. I've never tried this trick before,
> although I've used dozens of helicoils of all sizes. One is tempted to
> think that the threads tapped for the helicoil should automatically
> force the helicoil inserts to line up in such a way that the stud
> threads wouldn't get "confused" transitioning from the first insert into
> the second insert (if you get the sense of what I'm trying to describe.)
> For once, Google isn't providing any help with this question, so I'm
> asking for your experience and expertise.
>
>