Helicoiled my caliper threads today. Thought i'd share.

[Maverik]

I second that, do elaborate on double insert, interesting topic.

Mav

[landroversforever]

I'd imagine it involves one insert inside the other. Drill the hole out another size larger and have an insert the size of a normal Insert tapping drill.

[Lewis]

I assumed the same as Ross, you would need a vast selection of unusual pitch helicoils though - an M8 x 1.25 standard bolt would go into a helicoil which would need an M10 x1.25 threaded hole in which to be inserted. That's a standard helicoil, but to double up you would need a helicoil to suit that M10 x 1.25 thread, which in turn would need an M12 x 1.25 threaded hole. All these fine thread helicoils are available but it's gonna get expensive quickly. It gets worse for a larger original size, I don't know whether the larger sizes are available in a wide enough variety of thread pitches

Does any of that make sense to anyone?

[AMB]

Double inserts? Do you mean double depth?

No - one insert inside another.

We used Twinserts (http://www.helicoil.com.sg/HeliCoil-Oversize-Twinserts.shtml) but you can also get oversize helicoils (larger gauge wire) that require a larger hole for the same thread size as standard. In both cases, much larger contact area than for standard helicoil, therefore much stronger.

[Gazzar]

When doing the rocker shaft retaining stud holes on my tdi200 head I used a US product called a "big-sert" it was a machined insert, rather than a coil product. It worked well, and, though expensive, was cheaper than throwing out the head. A standard helicoil wouldn't work as the hole had already been bodged by a previous owner.

G.

[AMB]

When doing the rocker shaft retaining stud holes on my tdi200 head I used a US product called a "big-sert" it was a machined insert, rather than a coil product. It worked well, and, though expensive, was cheaper than throwing out the head. A standard helicoil wouldn't work as the hole had already been bodged by a previous owner.

G.

Yes, if you have enough metal. Then Big-sert or Time-sert bushes can work well. I've had no practical experience of Big-sert. Time-serts have a "top hat" section with rim that requires countersink to sit flush. Also a self locking mechanism which activates on first use. Does mean that you need a long enough bolt to activate the lock and, ideally, a little clearance beyond the insert to fully expand the self-locking.

[Gazzar]

You're right, they did have a top hat liner type flange. As I recall I milled this out with a hand drill. The mill was included in the set.

I'll post up the pics.

G.

[Gazzar]

I wrote a review on another forum, but in summary you drill, mill, tap and insert.

The insert driver tool puts the insert in place and also activates the lock tab sot hat the insert can't reverse out.

This was the problem:

[Gazzar]

I wrote a review on another forum, but in summary you drill, mill, tap and insert.

The insert driver tool puts the insert in place and also activates the lock tab sot hat the insert can't reverse out.

This was the problem:

[Gazzar]

The bodge didn't work and the rocker shaft broke (twice).

So I bought the big sert set.

[Gazzar]

I drilled out the hole.

[Gazzar]

I drilled out the hole again half way down to a wider diameter to allow for the flange, and milled it with the included mill.

[Gazzar]

more pics!