Sheared Bolt

Another interesting day of challenges.

My TF developed a squeak from the back right, on investigation the bottom mounting bolt for the alternator adjuster had snapped. I had only replaced the bracket a month or so ago with the adjustable version from MG Mania. Anyhow, I decided the simplest solution was to try to remove the broken piece that was flush with the block! Tapping it out with a centre punch was not viable as the space was too restricted. I had a dig around and found a drill bit that I could get in to try to drill out the bolt! After a bit of a struggle I managed to drill into the bolt but as luck would have it off centre! Trying to work the drill back around to recenter the hole caused me to snap the drill bit. Easy-outs haven't worked, I don't have a welder to try to weld a nut onto the sheared bolt, so clutching at straws a bit! Worst case scenario its an engine out job, best case is the Fairy Mechanic Godmother turns up waves a magic spanner and it falls out!!

If the broken drill is still stuck in there, you are struggling as even high speed steel drills are to put it mildly very hard. I understand the difficulty you're facing with limited space and the frustration that brings.
Do you know how much of the drill is still in there, and is it possible to grind it all back flush to remove the drill? You could then always drill out a larger size to remove the broken bolt and helicoil the oversized hole.

I’m not at home & don’t have a proper computer at hand so am using my iPhone which is remarkable for most things but for editing on t-bar it is lacking.
There was a post on suspension bolts a while ago & I referred to it on your post earlier & ended up sticking my thoughts on that!
You might find some aspects useful & you’ll find my earlier thoughts at the bottom.
M

The broken drill bit was about 3.5 - 4mm dia and there must be 4 mm of it stuck in! Unfortunately, the bolt sheared off flush to the block, and when I started to drill it out I drilled in with a centre drill about 6mm o/dia which was good but slightly off centre. I can make out the threads on the left side of the hole. Going to try another HSS drill this afternoon to see if I can get down the side of the broken bit but if it catches it will just break the next drill bit.

That last stanza was going through my head almost verbatim whilst I was reading it. I wish you all success, which is what you would expect from all of us.
M

I do this stuff for a living.
Now I’ve written previously about removing broken bolts……..pity you didn’t see it.

Before you even start, you need to equip yourself with a large selection of obscenities, profanities, blasphemies, oaths, curses, abuses and insults….. believe me you can never have enough, any shortfall in this regard will probably result in a brain aneurysm due to insufficient release of pressure!
This is an OH&S issue and no place to skimp.
Another thing to consider is appeasing the engineering gods, you will need to make a blood sacrifice, hopefully they will settle for some skinned knuckles, some bruises and a cut or two…… but you will need to be leaking blood or the job is doomed.

Now down to business…..

Rule #1, don’t attempt drilling without proper preparation first, you need to grind the broken area with a ball ended carbide burr in a die grinder, you can use a drill at a pinch.
You want to create a depression in the bolt.

Rule #2, in order to drill in the centre you need to use a centre punch to create a crater in the centre of your ground depression, be for drilling. If you miss the centre, grind the crater away with the die grinder and try again.

Rule #3 use a drill bit and drill that is properly suited to the task, a slow pneumatic drill is best, butt a good quality battery drill will do, by which I mean something that has very good balance and progressive speed control, cheap shit and handyman rubbish rarely have these qualities, Hilti and Bosch professional series drills are by far the best battery drills.
Next is the drill bit, yet again handyman rubbish won’t do, you need cobalt drills M35 (5% cobalt) or M42 (8% cobalt) with a 135 deg tip.

Rule #4, use a proper drilling cutting fluid, not rubbish like WD40!

Rule #5, first drill a 3mm pilot hole, for this I use the short double ended cobalt drill bits that are used for drilling out rivets, the reason is that they’re stronger. Then I use left hand cobalt drill bits to expand to hole, the reason for the left hand bits is that when they grab they will exert an unscrewing force on the bolt, remember to put the drill in reverse to use left hand drill bits and use a very slow speed, this will increase the chances of the bit grabbing in the bolt, work you way up in diameter, in stages so maybe for a M10 bolt start with a 5mm drill bit, then M7 and if it doesn’t come out with that then you would go to the size that you drill to tap a hole, in the case of M10 that would be 8.5mm.
Once you’ve done that the individual threads will be able to be easily removed.
Run a thread tap down through the thread of the bolt hole to clean up.

Rule #6, for small diameter bolts ( under M12) ezyouts an other bolt removal gimmicks, are a waste of time and money and are likely to break off in the bolt leaving you with a real headache, however they do work quite well in very large bolts over M30 and up to M75……not something that you’re likely to encounter in automotive use.

YOU DO NEED TO DRILL CENTRE AND STRAIGHT, and FFS don’t use crap, be properly prepared, take your bloody time and be careful……. Bugger it up and it will more than likely very costly to fix in time, effort, frustration and finances, as you are about to find out!

I thought I would persevere as no garage would touch it with a broken drill bit in it! At least the half dozen I called in to see wouldn't. Why take on a hard job when there are hundreds of easy ones out there!!

Tried to drill around the broken piece of drill but kept on snagging the bit and didn't want to break another one so thought I would try a centre drill again! I have an extension piece for my drill which is perfect for 6mm drill bit. Its held in place with the use of two grub screws! I had of course mange to loose one and decided to use the same threaded bolt. The one;y down side is as you drill its spinning around! As I was drilling using the centre bit, the bolt struck the block and snapped the centre drill in the hole.

Tried to encourage it out with anything and everything but failed. So, it can stay in there!!

OK, next question how can you tension an alternator belt when the original mounting hole for the tensioner is not available?

The block has threaded holes just above the original mounting point but 90 degrees in the other direction (same thread). So I came up with a solution using the old adjuster bracket (I had opted for an MG Mania rose jointed adjuster) which I still had and bolted that to the block, unfortunately the hole that was in it was in the wrong place so I drilled a new hole (or two, as the first one was too far in). A bolt was no good so I found some threaded bar and banged to put together an adjuster that could tension the belt.

That’s a cracking bit of scratch engineering & a credit to you for thinking at right angles to convention (in this case literally). You could only do this mod with a rose jointed adjuster, but there again if you hadn’t be using a rose jointed adjuster you wouldn’t have faced the initial problem. And you still retain the micro adjustment you wanted in the first place.
I’m glad you got it sorted; but nowhere near as glad as you, I’d like to bet.
M

You are going to love this!

After sorting out the alternator bracket tensioner modification. I thought I should do a quick tyre check before putting it back on! Yes, there was a nail in it, the head had gone and it was fairly small, so I pulled it out with a pair of needle nose pliers. To an instant hiss of escaping air! Great time to go off to the tyre repair shop. The one I normally use was closed! 1pm on a Saturday! So I found another who on taking the tyre off said, do you know you have a crack in your rim!

So! Guess I'm off to the specialist welders on Monday when they open!!

Could I recommend finding the root of the crack & drilling a small hole there. By doing this you will, in all probability, prevent the crack growing further into the casting, even after welding. It can easily be welded over.
However I would be looking for a replacement.
M

If it wasn’t for bad luck you wouldn’t have any luck at all!

I’d go for another wheel, it’s not worth arsing about with.

Back to you alternator pics, I see that you have used a helical spring washer on your bit of all thread, as the angle isn’t perfect that is doing nothing of any use, ( mind you helical spring washers no nothing useful anyway, both NASA and the US Navy spent millions of dollars doing exhaustive studies on them, and came to the conclusion that they don’t work )

I won’t use them, I’d replace the with nice thick hardened flat washers, and use a jam nuts against the nuts you’ve used, there is enough room for them.
I would’ve tapped that hole you drilled in the bracket.
To remove the broken drill bit will need either a EDM or carefully attack it with a carbide burr in a pneumatic die grinder.

One of these days, I’ll have the luck to have the time and someone handy to video me removing broken bolts for an instructional thread on doing this, unfortunately I rarely have the spare manpower and as these situations are usually time critical, I can’t seem to easily do this.

Looking again at those pictures I would question whether a reliable & safe job could be done economically.
In addition to drilling at the root of the crack the welder would have to grind into the crack to achieve adequate penetration of the weld. His welds (inner, outer & edge) need to connect in the same weld pool & it’s not like welding steel. Aluminium requires an an awful lot of heat input as it conducts that heat away from the weld site rapidly. I’ve seen “heat dams” used where a clay material is formed around the weld site, I assume to keep the heat localised, but I’m not knowledgeable enough to know how effective that would be in an application like yours.
Once done, if successful, you would need to create a surface at the periphery where the bead would seat & seal properly.
How well the wheel & tyre would balance up would have to wait until everything was done & how happy would you be to trust it on a track day?
Finally, if the rim has failed then the stresses within the casting have changed, that changed stress might be saving up problems for later.
Sorry, M