Sheared Stud On Bulkhead

[mowflow 67]

In a moment of absolute nuggetry I sheared one of the threaded studs on the bulkhead. It's the one that holds the triangular bracket which then holds the bracket for coolant hoses. I failed to realise it was a plastic clip that threaded on here so wound an m6 nut on which was a tad tight and caused shearing.

 

Anyway, I'm looking for suggestions on a repair. It's sheared with about 2-3mm protruding. A quick weld of a new stud (m6 bolt cut down) has been suggested but my issue is that my engine bay is resplendent in all new shiny paint and I don't really want to screw that and have to do a spot paint repair which will no doubt look crap.. Any suggestions?

[allanallen 528 2 Cars]

Drill it out and fit a bolt from the back?

 

Drill it out and riv-nut it so you can bolt the bracket on?

[Tom Fenton 1,541]

I have repaired a few of these. They way I do it is to carefully grind/linish the protruding broken stud flush. Centre punch it then drill through 5mm. Tap M6. The "boss" on the other side of the panel is just about thick enough to get away with tapping it.

Then from the other side, remove the fash with a countersink bit then fit a screw of appropriate length with a dab of high strength threadlock on it so it can't wind out backwards when you fit a nut on the other side. I prefer flanged button heads as they are a low profile. I use stainless because I have them to hand and it means the nut can't rust to the stud/screw.

Finished article looks as it should and works as it should from outside, and is hidden on the inside.

[allanallen 528 2 Cars]

You use stainless because you were a yacht builder in a previous life.....

[mowflow 67]

Looks like this is going to be another project within the project (curse my impatience). Hopefully I can get a drill in without having to remove any of the bits I've not long put back in the car.

[Tom Fenton 1,541]

Have you got the interior out? If so, you can do the repair as above all from the other side.

[mowflow 67]

Seats, carpets and most of the dash is out. Heater matrix is still in. I had a feel up behind the black rubbery sound deadening and the stud seems much higher inside than expected. Engine, box and subframe are all on but shafts and exhaust aren't in so will see if I have a drill small enough.

 

I bought my dad a makita cordless that's pretty short so might fit.

 

I've never been good at drilling things out so will try that with the rivnut as plan B.

Edited July 30, 2015 by mowflow

[mowflow 67]

Just thought i'd give a little update as this bastard stud has turned into a nightmare.

 

So I went for Toms solution of drilling it out. Not easy with the engine still in but I found a drill short enough and cut a drill bit down. Ground the stud flush screwing my lovely fresh paint work. Took ages to drill through as it turns out the drill bit I was using was made of toffee. After ages stood in a stress position using various levers to pressure the drill into the bulk head I eventually drilled through. Managed to get it right through the meaty bit of the stud on the inside of the car so a good amount of depth to take a thread. Got my m6 tap out and started to wind it in..... PING. The bastard snapped in the hole.

 

So now I have a hole in the bulkhead with a snapped M6 tap protruding into the cabin about 10mm. Pissed off does not even begin to suggest how fed up I am. I lay upside down in the footwell for about an hour trying to get the thing out but it looks like all the heater gubbins will need to come out to get any sort of access.

 

FML as they say.

Edited September 22, 2015 by mowflow

[Tom Fenton 1,541]

Oh dear. Sounds to me like your s*it drill has got the area too hot, which in turn makes it hard. The giveaway is needing excess force to make it drill through. With a good sharp drill I'm through in seconds with minimal force. Then you have tried to tap it and bust the tap off due to the steel being harder than the tap. Did you use any tapping grease/lube on the tap? Usual tapping technique is half turn in, quarter turn out, this breaks the swarf off.

Can you get hold of the end of the tap and back it out of the hole?

[mowflow 67]

I sacked the crap drill bit off after realising it wasn't going anywhere and bought a couple of 4.9mm and 5.2mm bits from a local tool shop. These were much better and the first one got through in seconds.

 

As for the tap. It seems that I misjudged how simple this was. I used no grease or lube and no half turn/quarter turn. I just battered right in. So it would seem it's completely my stupid fault.

 

There's none of the tap accessible via the engine side. It's snapped about half way into the hole. There's about 10mm on the inside of the car so i may be able to get some mole grips or similar on that an wind it through. I need to create some access space for that though. The heater fan housing is almost completely obstructing access. Would heat be a good idea when trying to get it out?

 

If all else fails my options may end up using a smaller drill to try drill the tap out or smashing it out with a hammer and punch. Either way it looks like there's going to be an m8 going in here.

[SkyQuake 70 1 Cars]

Bugger! This is going to be an absolute pig to remove.

 

As Tom has said, first try and backwind the tap if there's anything to get hold of. Be really careful not to do anything other than unwind. If you wiggle, bend or pull the tap it will just dig its barbs in and stay put forever.

 

There's not much strength to the bulkhead, so getting it hot and beating it out are out of the question. Forget trying to drill it out with cobalt drills or anything like that, the tap is much harder than the outer material so the drill will always wander down one of the flute holes.

 

One option you could try is cryogenically freezing it (using plumbers freeze spray) and grinding it out using the diamond grinding bit on the dremel. This works, but it does take absolutely forever. Plus the diamond bits are expensive, and you'll use at least a can of freeze spray. I tried this on an M8 I broke off and it took a whole weekend. I've never been so furious with anything in my life!

 

If you haven't snarled up the tap, and it has just torque failed as you're winding it in, I would suggest that you buy a Walton Tap Extractor. These use steel fingers which fit into the flutes of the tap so that you can carefully unwind it. I've not used one myself, but I have heard really good things about them. You can read about them here, and buy them here.

 

If this doesn't work, then drill another hole next to it and pretend you never touched it!

 

I hope this is helpful. Good luck.

[SkyQuake 70 1 Cars]

There's about 10mm on the inside of the car so i may be able to get some mole grips or similar on that an wind it through.

 

Whatever you do, do not try and wind the tap forwards, i.e, carry on in the direction of cutting, unless you are sure you're past the drafted (angled) faces of the tap. You must be on the parallel part of the tap to attempt this.

 

If in doubt, wind backwards.

Edited September 22, 2015 by SkyQuake

[Tom Fenton 1,541]

It sounds to me like it must be most of the way through. Try backing it off but if it won't budge i'd try and hammer and punch and belt whats left through into the car. You will probably have to go up to M8 then.

 

When tapping its always in 1/2 a turn, out 1/4 of a turn. With some experience you can feel when its getting tight. Obviously with bigger size taps they are a lot harder to bust than small M6 etc.

Drilling size for metric is size minus pitch. So for M6x1.0 then correct tapping drill size is 5.0mm.

Tapping compound/fluid/lubricant is essential. ROCOL do some of the best I have used.

[mowflow 67]

A few lessons learned the hard way here i guess.

 

The parallel part of the tap is definitely in. If i hadn't snapped it I could have wound it out and it would have been done. Instead i thought "wind this bugger right in and make sure it's done" idiot!

 

I'm going to try get access from inside and see if it'll wind in or out and think of a solution from there. If it won't budge then I guess i can just cut the tap sticking into the car, plug the hole in the bulkhead with weld (since the paint is screwed now anyway, drill another hole and put an m6 in from the inside tacked on the inside.

[mowflow 67]

Fixed.

 

More by way of miracle/sheer luck rather than any particular skill or ingenuity. In the end I resorted to pulling the dash out again and Shifting the heater assembly so I could get access. However, it was still a bit awkward so I actually found I could access the broken tap by sticking my arm down the intake for the blower under the windscreen.

 

In the end I wound it back out. Struggled with the last bit but after throwing the whole a-z of swear words at it and prodding with various jewellers screwdrivers, tweezers, picks, pliers etc it suddenly just popped out.

 

Amazingly I'd managed to create a perfect threaded hole (despite resorting to a punch and BFH at one point) so I now have a lovely new stud by way of a stainless bolt from the inside. Sealed it all up with liquid metal and just needs a wee blow over with paint on the engine side now.

 

Glad that's done and a valuable lesson about tapping learned. Thanks all for your advice and help.