Sheared bolt on bonnet spare wheel mount

Now without giving me loads of abuse for putting a second spare wheel on the bonnet...(which I'm doing because I bought my landy with the mount in place and it looks pants just having the mount poking out of the bonnet)...the feckless wonders who had it before me managed to shear the head off of one of the bolts that fixes the spare wheel retainer to the bonnet.

I have drilled the bolt out to 8mm, which is the largest diameter metal drill bit I have, but the remainder of the bolt is not budging from the bolt hole thread. The bolt is 12mm diameter (MRC4473).

I have a few options, unless you can think of something else:
1) Get a tap and die and cut my own thread and get a smaller diameter bolt to fit the new hole;
2) Somehow get the remains of the old bolt out of the bolt hole. It looks pretty rusty.
3) Keep drilling out the bolt and hope that the remains of the bolt crack up under the drilling.

Any of the above are going to involve me buying either a larger drill bit, a tap and die set, or some sort of bolt extractor, unless any of you have had any success by doing something else. Or is there a magic word I can say that will fix it? I tried XXX XXXX but it didn't work.

Whilst drilling I found it really useful to have a magnet to pick up the filings as they came out so that I didn't scrape them all over the bonnet and ruin the once spotless paintwork when I brushed them away...

Cheers!

Have you heated it up?

Die grinder or dremel, cut a slot in the bolt, then large screwdriver or other flat bladed object, I.e chisel wedge in slot and turn with mole grips or some other method of applying leverage, Make sure well soaked in penetrating fluid and to save paint try cold shock instead of heat, I.e co2 extinguisher to help break the rust . Shifted a few sheared bolts. With just the slot tho, good luck

blue beasty said:

Have you heated it up?

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Yeah, by mistake. I was being a lazy sod when I was changing drill bits (starting small and going up a size each time) as the drill I was using had a reverse gear rather than use the chuck key I was sticking it into reverse and holding to chuck to open it, slotting the drill bit in, then flicking it into forward mode before drilling. At 5mm I forgot to put it into forward gear again and after 60 seconds full speed drilling the whole thing got blue hot and buggered my bit.

I think I should have made the outer case hot and tried to cool the bolt body?

disco me said:

Die grinder or dremel, cut a slot in the bolt, then large screwdriver or other flat bladed object, I.e chisel wedge in slot and turn with mole grips or some other method of applying leverage, Make sure well soaked in penetrating fluid and to save paint try cold shock instead of heat, I.e co2 extinguisher to help break the rust . Shifted a few sheared bolts. With just the slot tho, good luck

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I salute you! I've got a dremmel somewhere. Excellent idea!

I've got a complete bonnet mount spare wheel carrier if ya want it. save ****ing about with a seized bolt.

redhand said:

I've got a complete bonnet mount spare wheel carrier if ya want it. save ****ing about with a seized bolt.

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Thanks Redhand - I'm going to try and fix it first but if I destroy it in the process I'll be in touch.

Also, it gives me a chance to use the Dremmel as it was meant to be used as opposed to engraving badly scribbled birthday messages on the backs of watch cases.