broken bolt

Today while I was riding 5K, this bolt broke :

Does anyone have any ideas how best to get the broken part of the bolt out of the fork, without destroying it? I could drill, but I’m afraid to damage the screw threading.

I don’t see an image, even if I cut and paste the url.

You can simply upload the image to this server (unless it’s huge, then you’ll need to resize it to meet the requirements).

There’s some problem with the url. If I type all the characters in, I can see and download the image. Here it is:

It appears that the bolt is flat at the break point. A flat surface makes center punching easier. The back of the bolt is certainly flat. Can the bolt be driven all the way through? Can you get a drill onto the back of the bolt or is the frame in the way?

Regardless, you’ll have to drill it. Carefully center punch either the break plane of the bolt or the back of the bolt directly in the center. Drill a hole smaller than the bolt. If you’re really lucky, the drill bit will snag the bolt and drive it all the way through. You’re probably not really lucky, though.

Use, buy, or borrow a screw extractor of the appropriate size. They are left-hand pitched so as you drive the extractor (anti-clockwise) into the hole you drilled, it grabs the bolt and unscrews it. You will need a tap handle to drive the screw extractor. Lubricate the threads of the bolt with penetrating oil.

Alternatively, if (and only if) the bolt can be driven all the way through either direction, use a larger drill bit in some kind of holder to screw the bolt out. Again, lubricate the threads of the bolt with penetrating oil.

Thanks for the advise. I am half thinking of just going to the local bikeshop, in case i do some permanent damage.

Sorry for the image. First the size wasnt good to save it on the forum, so i made it below 600px but then it said it should be below 97kb, which i couldnt with paint. Then some things went wrong when hosting it through free webspace.

If the bike shop is equipped to do this sort of thing and have experience doing it, that is your best bet.

I like the distorted reflection of you on the crank taking the photograph.

The reflection isn’t distorted. That is just how I look.:smiley:

Nothing to add to the advice, except that you may want to try to find someone a drill stand with some kind of a vise.

Although not the correct replacement bolt, you may like this one to:


Seems like he’s greeting us.

How did that happen? Very weak bolt? Bad luck? Overtightened?

Stainless bolts are difficult to drill. Doing it wrongly even for a moment could make it practically impossible to ever drill because stainless steel work hardens very easily. It is vital that the drill not be allowed to spin without cutting so it must be done at low speed with a very positive feed. Definitely don’t try it with a hand held drill.

I don’t think it could be drilled from the top due to the frame getting in the way of the drill. Moreover the location of the hole needs to be most precise at the bottom side if the bolt is seized must be entirely drilled out.

I would make a jig that the frame bolted into to ensure the mating surface of the frame is absolutely perpendicular to the drill spindle. Ideally do it in a mill rather than a drill press because a mill can be very precisely positioned with its cross feed work surface. The mill can can also be used to put a perfectly flat face on the broken surface.

Finding the centre of a damaged threaded hole as it is, wouldn’t be easy. Use the bearing cap to find the correct location. Assemble it to the frame and use it as a guide to drill out the first couple of millimetres of the hole in the frame. Do this turning the bit by hand to avoid any surprises. Ideally, turn and fit a steel sleeve to protect the bearing cap hole and reduce the bit size. Grind the tip off the drill bit if necessary to avoid hitting the bolt. This will give you a perfect circle in the correct position to work from. The thread is clearly wrecked here anyway.

Best start the hole with a centre drill. They do not drift like an ordinary bit does due to flexing.

If an ordinary drill must be used then be aware that the bit will drift from the centre mark and needs to be adjusted soon after starting. After centre punching, just start the hole so that the drill bit cuts a cone shaped hole. Assess the centricity of this hole. If it is off to one side then centre punch a row of points down the side the cone the hole needs to move toward and continue.

Then enlarge the hole with a progression of bits. Hopefully you will be able to use an extractor before you reach the full diameter of the thread root.

Otherwise, if the manufacture drilling and your drilling have both been done precisely, the bolt can be drilled out until only the thread remains and can be peeled out.

Worst case scenario you can have it drilled it out to a larger size and a Helicoil fitted.

Does the other end protrude past the frame? If it sticks out a bit you may be able to cut a slot with a hacksaw and remove it with a screwdriver.

I really have no idea how it happened. It had been screwed in like that for a several months and last week I rode trips of 15 and 10 km without problems. Then this weekend, when just riding on asphalt there was a loud pang and that was the broken bolt.
The other bolt that didn’t break was screwed in deeper actually.

I find it very odd it broke so deep inside, and not at the edge or at the head.
Anyway, good luck with the drilling. Maybe make sure the thread is OK after the job. And let us know if it worked out (or not).

Have considered inserting the other hub cap bolt and screwing it in so that it forces the broken bolt to screw out :thinking:

Hey that is a good idea. I will try that before bringing it to the bikeshop :slight_smile: why didn’t I think of that right away.

Doing so you will only break the existing thread.

How would it break the existing thread? The hole for the bolt goes all the way through to the top already.

I reckon worst case scenario would be if I can’t use the current hole anymore, I can take a bolt with a nut on the other end and just screw it all together again.

Because it will jam against the broken bolt and be apt to strip the threads of the softer material. Jamming two bolts together doesn’t equal one of the bolts turning out.

I wish you were local because I’d have you up and running in just a few minutes.

Removing the broken bolt should be as easy as center punching the existing bolt, drilling a small hole careful in the center, and then using an ez-out/bolt extractor to back the bolt out. If your lucky the drill bit will catch the bolt and spin out the back side without even having to use the ez-out. In worst case scenario the threads in the frame may be damaged and then it would be best to drill them out and heli-coil the hole to the factory bolt size.
In all reality if your asking how to deal with the problem in the first place your probably not to familiar with the tools and your best bet would be to have a automotive machine shop repair the frame for you or someone experienced to guide you through the process. I say automotive shop because steel bolts braking off in aluminum cylinder heads is super common and very easily fixed, most of the time…

That would depend on how stuck the remaining part of the bolt is. The ez-out has to be able to apply enough torque and a “small hole” might not fit a large enough ez-out to apply that much torque.

But if you are unlucky the break in the bolt thread will be jagged and misshapen and damage the thread as it drives out through the back.