Stripped bowl threads on carbs Helicoil guidance needed.

[McCabe-Thiele (Ted)]

I have a couple of stripped threads on two seperate carb bowls that I need to Helicoil.
After a lightbulb moment I realised I had an M4 repair kit that I bought a year or so ago & never used.

I've viewed a video on U tube so know about the tang that needs knocking out. It is also obvious that my Helicoil type inserts are too long. The Tap that came in the kit is a taper type so am conscious that it will soon contact the carb body as it is screwed in. The size is shown as M4*0.7.

Any tips from someone who has done this would be appreciated, can this be done with the carbs on the mounting bracket or do I need to remove them and hold the body in a vice taking measures to avoid the jaws marking the carbs?

Is it best to use a dremel blade to reduce the length of the Helicoil or are they available in the right length without buying a hundred?
I've tapped out threads before but never fitted my own Helicoils.

[K2-K6]

You'd need a "plug" tap to have parallel thread into blind hole Ted, else the helicoil will also be forced into a taper as it screws is.

The helicoil winds in really easily, led by the tang, it contracts it's own spiral to make it really easy, but won't back out as that same spiral expands in reverse. Probably the easiest bit to do in reality.

Taper tap is to lead the tap into the hole by not trying to cut on its leading edge, and so gives more assured vertical to bore approach without much effort. Plug tap,to finish is engineering routine.

I'd wind the insert in then carefully cut off the excess with dremmel cutting disc if they are too long.

Tap carefully with plug, plenty lubrication and clean the bottom of the hole out as you go to get debris out of cutting zone.

[McCabe-Thiele (Ted)]

The tap that came with the kit is marked as STI4*0.7HSS the tip is pointed - is a plug flat at the end as well as no taper?

Any links to source a Plug Tap for the Helicoil  as it's not a standard M4 tap?

Is this the type I need?

.https://www.ebay.co.uk/itm/156252954833

[Bryanj]

Ted, long before dremels we had small triangular files and would file a V groove in thefitted coil just into the hole and break off the excess.
Let me look at my sets and if the M4 is a plug tap you can borrow it for post costs

[McCabe-Thiele (Ted)]

Kind offer Bryan might be worth me just buying a flat ended tap from a local engineering supplier - it will come in handy in the future no doubt.

[Bryanj]

Its NOT a standard tap Ted, its a special that has the m4 profile and pitch on a bigger diameter to accomodate the coil widthx2

[McCabe-Thiele (Ted)]

Thanks I understand that Bryan.

[Bryanj]

I have never found any firm selling just the taps except heliciol original and they were expensive

[DomP]

I had this exact problem Ted, in the end I cut a thread it in af far as i cold before hitting the carb body then trimmed a coil to fit.  Not ideal as there is very little thread length to bite on but it's working  for now.

[ka-ja]

In my engineering past when desperate, grinding a taper tap back (short) is one way of creating a bottom tap, if you have a spare.

[JezzaPeach]

Hi Ted, I had one go and (for now) got away with a longer screw which reached some unused thread, and not over- tightened. Just a thought.

[McCabe-Thiele (Ted)]

Hi Ted, I had one go and (for now) got away with a longer screw which reached some unused thread, and not over- tightened. Just a thought.

I tried that by leaving the washer out - I'm going to do it properly - one day next week if I have a spare box of roundtoits.

[Bryanj]

Got a squaretuit!

[McCabe-Thiele (Ted)]

My box is square - I suspect it's still empty!

[Matt_Harrington]

Ted, I replaced about half of the threads on my spare 400/4 carbs with helicoils. I use Loctite 648 when inserting then trim off any helicoil AFTER it has cured with the ol' dremel.