I busted a bolt in the eyelet on the frame for the rear rack. The threads were destroyed prior to removing the bolt and snapped the bolt trying to get it back out.

I have been doing searches online to figure out the best way to remove it and then re-tap it for another screw but everything I am finding on the subject is more geared towards working with bigger bolts on vehicles and the like. Also, most of the things I am finding about it or dated and was hoping to find a more detailed explanation of how to do this specifically for a bicycle.

Thanks

There are two potential real solutions, drill and retap or use of an easy-out or speed-out extractor bit. Extractor bits are more commonly used when the head is stripped but still exists, drill and retap may be the only solution for a small bolt with the head sheared off. There is a third solution of welding a nut to the top of the broken bolt but that is drastic and could do more harm then good on smaller bolts.

A picture of the current situation would help in offering one solution over the other or at least provide a guess about the size of the broken bolt.

An easy out bit would require you to drill into the center of the stripped head or the end of the broken off bolt with a left-hand-twist drill bit particularly sized to the extraction bit (spiral left hand thread) drill and extractor should be sized as small as possible ti fit within the diameter of the existing bolt comfortably.

Drill and retap is intended to drill and retap the bolt hole (drill bit is precisely sized to the tap size) again drilling into the center of the broken bolt and then using the tap to clean and shape the threads of the original hole. You can use the matching hole on the other side of the frame to determine the actual thread size with a tap set.

I like to spray a corrosion breaking oil like PB blaster or similar on the remains of the old bolt to help it clear the old threaded hole and use a center punch on the bolt so that the drill bit doesn't slide off the bolt. If the broken bolt is uneven, use a flat file or grinder on it before using the center punch or drill to prevent the bit from drifting off center.

I have also been successful in using a small pair of channel lock pliers to grab the other end of the bolt as it passed through the frame and extracting it by using a tightening method as long as the entire head was sheared off, again first spraying the broken end with PB blaster.

Here are some links to these tools,

https://www.homedepot.com/p/Vermont-...1829/202850653

https://www.homedepot.com/p/Ontel-Sp...0264/205110987

https://www.homedepot.com/p/DEWALT-M...1450/204787392 (metric sizes)

https://www.homedepot.com/p/DEWALT-F...1451/204787386 (SAE sizes)

I've found drilling works pretty well for rack eyelets. Sometimes the torque of the drill is enough to drive the remains of the bolt out the back of the eyelet.

You don't really need a left-hand bit for this job, since the eyelet is not a blind hole.

If the frame and bolt are not aluminum or titanium or the newest fancy stainless alloys (these metals "gall", or cold-weld to themselves very easily), then drilling is your best bet. If the broken bolt is proud of the frame, I'd file the top flat and use a center punch to get the drill started evenly. I have no luck with hand-held drills, so I'd actually try to find a way to hold the thing down, clamped, so that I could use my drill press. This would avoid the drill wandering around and drilling into the frame rather than the bolt. I'd probably start with a drill much smaller than the bolt diameter, to ensure I had a centered pilot hole.

If the frame is one of the easily galling alloys, one solution that machinists use is called electrical discharge machining, or EDM. Find a machine shop that will do this for you. Worth it if the frame is an expensive titanium one.

If the frame and bolt are steel, and the bolt shank sticks out enough, another machine-shop solution would be to weld a nut to the shank. Simple stick welder can do this. Then you've recreated a bolt, and the heat from the welding process may have loosened up the threads.

But it sounds like the bolt is galled into the frame. Unless you are awfully skilled with a hand-drill and have a steady hand, I'd fixture for the drill press, or find someone to do EDM.

head, if broken off, remains can be screwed in further until it comes out the other side, too..

not easy but can be done

+1 for left hand bits



straight fluted extraction tools work best. be sure to use a proper tap wrench to turn it






take your time



then when retapping the hole, try using the exact same size as was messed up, so you can continue to use the conventional M5? bolt

it's all freaking annoying & expensive (bits & the other tools). you're not alone

Hmmm, let's see: Bolt broke while backing out and "threads were destroyed prior to removing the bolt." We don't know which threads or where damaged, but using an extractor is likely to result in a broken extractor.

Maybe try some heat and/or penetrating oil, and turning out the bolt from the other side.

Maybe consult with someone in person who has a lot of experience with stuck small screws (like an aircraft mechanic).

No, an extractor isn't going to work for me. I actually really screwed up the threads trying to put the screw in to begin with and really jammed that screw in there forcing it. At the moment, I was in a rush, knew something was wrong when I was threading it, and continued to force it through anyway because I was having thread problems to begin with. In my minds eye, I figured by forcing it I would force it to rethread the way it was wanting to go. I literally snapped the screw flush with the frame trying to force it in further under the gun. That sucker is never coming out without drilling the entire thing out now.

And I am worried about doing it by hand since I don't have a press, or even a real drill for that matter. I don't even think that I really need to get the broken screw out, because there is another eyelet right below it that I was able to use for the rear rack instead. I used that secondary eyelet hole that is common on bikes right below it on the frame. I can live with it the way it is, but I was more thinking about for when I eventually sell the bike. Don't want the next person to get stuck with the problem. And it is a good opportunity for me to learn another skill since I am somewhat mechanically inclined, just haven't had the opportunity to do this exact thing.

After I drill it out and have it tapped again, do I need to worry about anything specific about where the new metal in the new eyelet is now exposed? Nothing special has to be done there right? I can just screw a screw back in the hole after tapped, just obviously the next size up for the new hole. It was originally a 5mm hole in there, so I am assuming when I get done it will be a 6mm? The frame is aluminum.

I have to take my entire rear rack off to get a good picture so I will get one up later.

a drop of any readily available lube would be more than adequate in the newly threaded hole

brilliant about not having to do it. another option is p-clips. in case you want to mount a rack & fenders at the same time

but go buy a drill, the correct size left hand bit & give it a try. you might get lucky. that's how tool collections are started. when the need arises you add a tool as you go

If you do drill out the broken bolt you really don't have to rethread the hole. Drill an M5 clearance hole and use a new bolt and nut to attach the rack.

Tap and die metric set

https://www.homedepot.com/p/DEWALT-M...1450/204787392

haha right on! plain as day!

Seems to me if you just drill through the bolt as is with the proper sized bit for a 4 or 5mm? ( whatever the old bolt size is) tap and just re-tap. It will most likely chase the remaining bolt material out and leave you with some nice clean threads in the process for a new bolt.