Timesert or helicoil...?

[265bhp]

I need to repair a damaged 7/16 UNC thread on the cast steel differential
The female thread has stripped
It's to hold one of the rear brake callipers...each of which which has 2 bolts

Timesert seems to be a lot more expensive but I want to do the job properly

Thoughts please

Thanks
Jonathan

[paulsco]

Hi Jonathan,

I have used Helicoils many times with great success although I am led to believe that they may be a problem with bottomless holes as they can screw right through.

I personally have not had any problems.

I have not used Timesert's; they are more expensive but appear to be more solid.

Here is a youtube video giving reasons why the Timesert is better.

Paul

[265bhp]

Thanks a Paul
I had seen that one...which made me wonder

[JagWaugh]

For the caliper mounting holes the helicoil will be fine. The big problem with either is getting the hole drilled/tapped at 90 degrees.

[PeterCrespin]

Your proposed application involves mainly shear forces trying to move the clamped caliper around with the disc. I would think helicoil would be fine.

[Series1 Stu]

Hi Jonathan

The time sert appears to be a good solution but there is nothing wrong with the helicoil if fitted properly. Just follow the instructions and all will be well.

Regards

[265bhp]

Thanks guys

[E600]

I am curious, how did the thread get stripped given its accessibility. I presume no extension bars were bent in stripping a 7/16th thread? Do you frequent the gym?

[265bhp]

Hi

It's a mystery....first calliper went in fine...just needing 2 spacers to centre on the disc, second one likewise...it's all a bit tricky getting the spacers/bolt/washer and calliper lined up but once I had I realised I was just screwing the bolt in and getting no-where....perhaps the threads were damaged when I disassembled...perhaps there wasn't much thread left and I finished it off with the trial and error of getting the right number of spacers....

Just one of those things..... ...time to learn how to helicoil then...

J

[rfs1957]

I would second JagWaugh's comment regarding the 90° approach.

This has always seemed to be the key, the absolute key, to getting them to work for me - because it's those critical first threads that determine how the insert winds into place.

These are pictures I took a few years ago, but never posted, when reclaiming some cam-cap threads.



I can't remember what the "approach" to the area is like, for you, for the calipers, but when I can I use an offcut of 3/4" x 1" ground steel bar that I bore "tight" for both the tapping drill size, and the clearance size for the Helicoil tap.



In this way, in situations in situ where you can't do both drilling and tapping operations on a mill, by clamping (not seen here) the slab to the workpièce you have a much better chance - freehand - of getting the drill through square, and then, by swapping holes on your guide, getting the tap to follow the axis of the hole you've just enlarged.

I've certainly done 3/8" holes this way, and would think 7/16 possible with more care, especially in an application where, as Peter C says, we're looking at shear where alignment is not super-critical.

With 1/4 and 5/16" it's a breeze, of course.

Unfortunately, in an attempt to democratise the process, the cheaper kits (like the Recoil ones made in Australia ? see below) have simplified the tooling to an extent that - I find - makes it harder to get the Helicoil insert in correctly.



The better stuff involves a cylindrical threaded guide tool (below, see the tool on the left) inside which the helicoil is threaded first, which pre-constrains the coils and - critically - means you can "feed" the insert into the hole in the work-piece with a little compression to maintain the pitch during the operation.



"Feel" is everything when doing Helicoils.

Cheaper and simpler kits just rely on the slotted-end insert driver (see below) to screw the insert into the tapped-hole, and so there is no pre-constraint on the insert and your efforts are located entirely on its leading spire - theoretically the adjustable collar (seen to the left) is meant to get round that, but it's not easy to dose.



Very often, in my experience with these kits, you end up with the last turn of the insert refusing to adhere to the sequence of the previous ones - and you've got to start again. I've never failed to get these to work, but it's trickier, can take a couple of attempts, and is not quite as predictable ?

Below is a set, including spark-plug threads, where the guide noses are apparent ; these also have the double luxury of using stepped taps where the first thread corresponds to the damaged one that you're trying to replicate, into which you thread the tap - then next comes the bigger diameter thread you need for the Helicoil insert, which is then pulled through by the initial thread.

So no drilling, and no problems with alignment - but probably limited to aluminium, and obviously no good with blind holes. I confess to even having done this, in emergencies, with heads in place - ahem, plenty of grease to retain the swarf, and lots of compressed air afterwards.



However you do it, I would accept that you're going to have to practice with a dummy run or two on a test-piece before you go for the real installation ?

[265bhp]

I have also been guided to E-ZLOCK type applications which being solid like a Timesert are presumably more reliable than a Helicoil...rather like the look of these I have to say

http://www.amafasteners.co.uk/products-page/e-zlok-unc