Topic: Broken Bolt (Read 8003 times)

ivanidea · « **on:** July 15, 2007, 11:23:13 AM »

I managed to remove the front bumper on my TJ, but one of the top bolts did break.

Since I will be installing a winch, I need to remove and replace the bolt.

I spent 2 hours trying to drill a hole, but only manged to make a hole approx 4mm deep - not enough for the screw extractor.

I have been using HSS (Black & Decker) and titanium drills without any success.

Any suggestions? Also, what size bolt do I need since an M12 is the wrong thread, so I assume I need an imperial equivalent.

The of the nuts is about to break away from the chassis, so when I tighten (or remove) the bolt in the future, I expect it will break. Since I am not a welder, I was thinking of cutting a hole (or 2) in the front bumper, which would enable me to get a spanner into the chassis. A part from filling up with mud, would this be a potential problem for the future?

Ivan

chrisjones · « **Reply #1 on:** July 15, 2007, 11:44:45 AM »

It sounds like you have a high tensile bolt there. I'm surprised that you haven't had more luck with the drilling though, what kind of drill are you using?

Go to a proper tool suppliers and get 3 or 4 decent drill bits including some smaller than the hole you need.. Make sure your drill isn't turning too fast and use some light oil to cool the drill bit and clear any swarf then start with the smaller bits and open the hole up after. It's important that you don't drill for prolonged periods because, if the bit gets too hot it will lose it's edge and be useless.

As for the nut, you're going to need to cut a fair sized hole in the bumper to get a spanner to it. It's better to get it re-spot welded. Maybe leave that bolt out until you can get to someone with a welder. :wink:

shep · « **Reply #2 on:** July 15, 2007, 12:31:36 PM »

from memory the bolts are coarse Witworth :?

Mik · « **Reply #3 on:** July 15, 2007, 01:15:08 PM »

1/2" UNC

Bubba · « **Reply #4 on:** July 15, 2007, 09:11:03 PM »

DarrenR · « **Reply #5 on:** July 15, 2007, 09:58:00 PM »

Ivan, I am sure someone local to you will tack a weld on the nut on the chassis, if you come down to surrey I'll do it for you.
have you got any bolt sticking up, as irwin do nut extractors which bite into the bolt and undo it, jon used them to remove rusted LR stubs in the field at SS when he punctured his tank.
machine mart sell them also screwfix,

Darren.

Dave69 · « **Reply #6 on:** July 16, 2007, 09:40:32 AM »

if the bolt is siezed in place good and proper dont use stud extractors as they have a chance of breaking themselves, which will just add to your problem. use a small drill to start with in the centre of the bolt ( if possible) and use oil to help the drill cut. when through drill again with a slightly larger drill untill you get to the size required. what you can then do is retap the thread and this should then clean out the old thread ready for a new bolt. or you could go oversize and use a metric thread 14mm, the captivated nut should be big enough to thread to this size

JamesH · « **Reply #7 on:** July 16, 2007, 05:57:49 PM »

I'd go with what has already been said, especially to drill and tap, either 1/2" or oversize (M14).

Spend a decent amount on quality drill bits (tungsten carbide?), oil and take it slow - the drill should do the cutting. It's no good pressing down like a loony and spinning the bit at 30,000 rpm (I speak from experience, I'm not accusing you of doing anything quite so silly :oops:

)

You can spot weld items like nuts on with a £50 'buzzbox' arc welder and very little skill (again, from experience) and think of all those little jobs you could do with it

James

ivanidea · « **Reply #8 on:** July 17, 2007, 09:09:06 AM »

I know it sounds wrong to use HSS drill bits at the slowest speed, but that's what I was doing this time. (I remember melting a drill bit trying to drill a hole in the front bumper a few years ago).

I was also thinking the screw extractor might not be upto the job, since it took a 3' breaker bar to remove the other bolts (and to break this one).

Since the bolt is approx M12 diameter, I am now thinking of drilling a 10mm hole (or whatever is required for an M10 bolt) then tapping (is there no end to the expense for a simple job), assuming this would be strong enough, with the remaining 3 original bolts. I know I have access to stainless metric bolts at work, but I think they are weaker than the current bolts.

It's over 20 years since I had a go at welding (electric arc and acetylene) and I did the best (or worst) example in the class of how not to do a weld!

Ivan

Dave69 · « **Reply #9 on:** July 20, 2007, 08:20:10 PM »

stainless bolts are a good choice but check you know the grade. A2 is the norm and A4 is marine resistance. they should be the same tensile strength of normal bolts unless marked with a number higher than 8.8 on the head, cap head bolts are high tensile to start with. even with stainless it is advisable to use an anti sieze compound on the thread.

mattiemjbb · « **Reply #10 on:** July 21, 2007, 01:58:32 PM »

is there space to fit a grinder in and grind the head off, i had to do that with one of the radious arm bolts on my zj took about 5 mins compared to about 3 hrs trying to drill it :swearmad:

Ric Jacques · « **Reply #11 on:** July 21, 2007, 09:43:27 PM »

Tungsten carbide drill will eat through it.

Remember 'LOW SPEED HIGH FEED'. We're talkin REALLY low speed here.

HSS drills on a high tensile bolt (bumper bolts should be grade 5 at the minimum - preferably grade 8 ) will blunt in no time at all. You might get away with using Cobalt drills which are a bit cheaper than Tungsten.

Ric Jacques · « **Reply #12 on:** July 21, 2007, 09:46:44 PM »

Quote from: "mattiemjbb"

is there space to fit a grinder in and grind the head off, i had to do that with one of the radious arm bolts on my zj took about 5 mins compared to about 3 hrs trying to drill it :lol: :lol:

daggie · « **Reply #13 on:** July 21, 2007, 09:56:24 PM »

RTFP, :lol: :lol:

Ric classic

ivanidea · « **Reply #14 on:** July 23, 2007, 09:17:46 AM »

Tungsten drill bit (even at very slow speed and oil cooled) made no difference.

I have now fitted the winch (whilst it was not raining) held on by 5 bolts instead of 6, and have had to ditch one of the recovery hooks (no good with only one bolt).

I looked at buying some more tungsten drill bits, but B&Q only had coated ones, which I presume are not as strong as tungsten only (if they exist).

The bolt is a grade 5, with OF as additional marking. It would have come with the recovery hook, due to the extra length.

I shall probably keep having a go at drilling when I get a few minutes (and the weather is dry).

Thanks for all the advice and suggestions.

Ivan

bonza · « **Reply #15 on:** August 06, 2007, 03:20:35 AM »

Quote from: "shep"

from memory the bolts are coarse Witworth :?

not coarse whitworth

it is 1/2" UNC = 13 TPI

1/2" bsw = 12 TPI

as far as drilling out the broken bolt goes.

make sure the drill is sharp and on very slow speed.
apply plenty of pressure and apply some sort of cutting compound

hey. my first post on this forum. g'day all

Manda · « **Reply #16 on:** August 06, 2007, 10:27:25 AM »

Hi Bonza, hop over to introductions and say hi.

Bubba · « **Reply #17 on:** August 06, 2007, 03:10:00 PM »

ivanidea · « **Reply #18 on:** August 06, 2007, 03:32:18 PM »

Many thanks for all the replies.

Does anybody know the size of the bolts which hold the front swaybar to the chasis are? I would have thought the service manual would have given bolt sizes, but I haven't found it if it does.

I need to use longer ones since I have added a winch plate.

Again, I assume they will be UNC.

Ivan

Bubba · « **Reply #19 on:** August 06, 2007, 06:08:47 PM »

mayo is exelent cutting fluid but gets a bit gritty if you eat it afterwards

Author Topic: Broken Bolt (Read 8003 times)

shep

Mik

mattiemjbb

Ric Jacques

Ric Jacques

bonza