stripped heat shield mounting lug - helicoil?

[Vintage Veloce]

The exhaust on my old dirt bike has a lug that is stripped out. The lug is one of four used to mount a lightweight heat guard.

The lug is 6mm - 1.00 pitch and about 8mm deep.

I'm trying to figure out how to repair it.
*edit: This repair has to leave the exhaust and heat shield looking as they were originally. This is a restoration project.*

I bought a helicoil kit, but actually using it looks to be a problem.
Drilling out the lug is at high risk of drilling through the exhaust if I drill to far. And then the tap won't tap all the way to the bottom of the lug anyway. Even my "bottom" style tap is going to leave at least 3mm of the bottom of the lug untapped. So that would leave me trying to cut down the helicoil insert to 4mm length, or something like that.
It just doesn't seem like that is going to work... am I missing something?

Removing the lug and replacing it seems like a good idea, but again a delicate cutting job on the thin exhaust metal.

I mentioned to a welding friend that maybe I should have the lug's hole welded up in place and re-tap it, but he said the weld material would be very hard, and I would still have the problem of tapping the shallow closed bottom hole.

I find myself now considering filling the hole with some kind of high temperature filler and tapping that. (JB-Weld?) It's an exhaust, so I'm not sure various fillers would really stand up to that. It will see rather heavy vibration.
And again, tapping the shallow closed bottom hold is the problem.

So... any easy ideas I am missing?

 

[Vintage Veloce]

I will add I have considered this idea, but I don't like it:
Have the full perimeter of the lug welded to the exhaust, gas tight. Then intentionally drill through the lug and into the muffler, so that it is easy to tap and helicoil. And them use sealant on the screw when I assemble the heat guard, so the lug/bung will now be sealed.
But this just doesn't seem "right".

 

[CJM8515]

Tap for 1/4" standard bolt. Drill it out use a nutsert.

 

[Bigblue&Goldie]

If you are just going for function stainless steel band clamps or hose clamps works well.

 

[Vintage Veloce]

If you are just going for function stainless steel band clamps or hose clamps works well.

This is a restoration, so it has to look original.

 

[joe_padavano]

That boss was threaded before it was welded to the exhaust. If the hose clamp idea doesn't work for you, the next quick and dirty solution is to find a self-tapping bolt that you can use. Next option would be to cut the boss off of the exhaust, repair the threads or replace it, and weld it back on. Finally, consider welding a threaded stud into the boss and use a nut to retain the heat shield.

 

[joe_padavano]

This is a restoration, so it has to look original.

Well, in that case, your only option is to cut the welds holding the boss to the pipe, fix the threads, and re-weld.

 

[MattT]

Removing the lug and replacing it seems like a good idea, but again a delicate cutting job on the thin exhaust metal.

Cut a little high then grind the welds down to the pipe.

Or if you can get away with spacing the heat shield further from the pipe welding a nut on top of the existing boss would be the quick and easy fix.

 

[Vintage Veloce]

Tap for 1/4" standard bolt. Drill it out use a nutsert.

Nutserts I see are all way too deep.

 

[Vintage Veloce]

Joe and Matt,
you may be right: I may have to try and find someone with more cutting and welding of this kind of stuff than I personally have. I'd make a mess of it.

 

[CJM8515]

If your going for full resto its probably a better idea to weld it shut, then drill and retap it. Nutserts are about 1/4-1/2" deep.

 

[harley jim]

I would cut it off repair it then weld it back on. I ran a job shop in the fab shop so we were doing that type of stuff all of the time

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[Kenstone1]

Carefully cut of the stock lug with a DREMEL/CUTOFF WHEEL.
Fabricate a new lug to the OEM dimensions.
Clamp/tack/Tig the new lug onto the muffler in the stock location.
The only proper way to do it to remain stock (looking).
not rocket science,

 

[Kevin54]

HeliCoil it. Grind some of the tip off of your drill bit so it won't cut. All you need is a small lead on the drill and a flat bottom to stop you from drilling through. If you have a pointed tap, start the hole with the tap, back it out, grind the tip off of the tap, then finish tapping. Clear out the chips, insert the HeliCoil, BUST THE TANG OFF AND REMOVE, then cut any coils off that is sticking out the top. 30 minute job, tops.

 

[rlitman]

HeliCoil it. Grind some of the tip off of your drill bit so it won't cut. All you need is a small lead on the drill and a flat bottom to stop you from drilling through. If you have a pointed tap, start the hole with the tap, back it out, grind the tip off of the tap, then finish tapping. Clear out the chips, insert the HeliCoil, BUST THE TANG OFF AND REMOVE, then cut any coils off that is sticking out the top. 30 minute job, tops.

This! Treat the helicoil drill bit and tap as consumables. The drill bit doesn't need a point, because it's just cutting out the threads. The tap needs a lead-in to start, it needs less and less as you progress inwards.

 

[kerrynzl]

Nutserts I see are all way too deep.

Is this on an exhaust pipe or muffler?

If so, you should be able drill right through. The hole will end up with a bolt plugging it anyway .

I would drill it through , then countersink the top slightly and use a countersink nutsert

You can also get "blind" nutserts

 

[APEowner]

I'd just cut off the lug and weld a new one on. That's a 30 minute job including making the new lug.

 

[rlitman]

Is this on an exhaust pipe or muffler?

If so, you should be able drill right through. The hole will end up with a bolt plugging it anyway .

I would drill it through , then countersink the top slightly and use a countersink nutsert

You can also get "blind" nutserts

Two problems with a nutsert. The biggest one is grip length. Nutserts only work in a narrow range of grip lengths, with most being made for sheet metal. They will not expand and/or grip properly with this much insertion depth.

Then there's the seal issue. Yes, a blind insert would solve this, but if you use an open one, even the smallest leak will lead to awful freezing up of the bolt.

 

[harley jim]

I'd just cut off the lug and weld a new one on. That's a 30 minute job including making the new lug.

X2

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[Jack84]

Can you go a step up and make it M8?

Chopping the old lug and welding on a new one is a good idea too.