Alright, let's get to it. This week for our Q&A post I’m going to cover the dreaded process of removing broken off bolts from their stuck fortresses. An outline of the process usually entails saying your favorite cursory phrase, repeating this phrase numerous times, then trying to use an extraction tool to get the broken off bolt out. The success of this endeavor varies widely depending on the situation, however I’ll attempt to share some helpful tips with you in case you find yourself in a jam.
My latest purchase, a 2011 KX250F, came with all sorts of subtle problems that required attention. Not only did the engine need a lot of work, but the bolt securing the kickstart pedal to the shaft had broken off inside the shaft. Kickstart shafts are not cheap new, and used ones were still more than I cared to spend on a part, which was perfectly fine apart from the broken bolt. So, I chose a day where my patience level and spirits were good and decided it was time to get the stuck bolt out.
In this write up I’ll cover how to remove a broken bolt using a screw extractor. Screw extractors can be found at most hardware stores, come in a variety of sizes, and are cheap. More elaborate extractors can be found through sites such as McMaster-Carr which may or may not work better for your given application.
It would be far too easy for a bolt to break evenly and flat. Instead, an uneven breakage point is characteristic of a broken bolt. Depending on the severity of the unevenness of the broken face, it can be next to impossible to get a drill bit to track true, even with a punch mark to get started on the right track. To help the drill bit center itself and to locate it so that it drills in the center of the bolt I like to use a rotary burr or a grinding stone to create a smooth and shallow impression.
In this write up I’ll cover how to remove a broken bolt using a screw extractor. Screw extractors can be found at most hardware stores, come in a variety of sizes, and are cheap. More elaborate extractors can be found through sites such as McMaster-Carr which may or may not work better for your given application.
It would be far too easy for a bolt to break evenly and flat. Instead, an uneven breakage point is characteristic of a broken bolt. Depending on the severity of the unevenness of the broken face, it can be next to impossible to get a drill bit to track true, even with a punch mark to get started on the right track. To help the drill bit center itself and to locate it so that it drills in the center of the bolt I like to use a rotary burr or a grinding stone to create a smooth and shallow impression.
Once the impression has been started, a center drill bit can be used to good effect to start the initial hole.
After a nice pilot hole has formed, the drill bit size recommended by the manufacturer of the extraction bit can be used to increase the depth of the hole. The exact hardness of the bolt will be dependent on its grade and it could be very hard to drill. Be very careful to keep the bit aligned perpendicular to the hole and not to apply too much pressure to the bit, causing it to break. Breaking the drill bit off inside the stuck bolt pretty much means the game is over if it can’t be removed. Drill bits are even harder than the bolt and next to impossible to get out if they break off in the hole. Run the drill at a very slow speed to avoid overheating the bit and apply oil to the end of the bit to lubricate it.
The hole will need to be drilled fairly deep in order for the extractor bit to “bite” correctly. A feel for hole depth can be gained by examining the taper of the extractor and seeing how far down into the hole the bit will extend.
Once the hole is deep enough the extractor can be fit into the hole and slowly turned to get a feel for how stuck the bolt is. The bolt may or may not turn depending on how stuck it is. The worst thing that can happen is the extractor is turned too hard causing it to break off inside the stuck bolt. This makes things even more complicated and should be avoided at all costs. If the bolt doesn’t turn right away with moderate force, don’t push the issue. Instead, use a torch to heat the end of the shaft surrounding the bolt threads.
Once the hole is deep enough the extractor can be fit into the hole and slowly turned to get a feel for how stuck the bolt is. The bolt may or may not turn depending on how stuck it is. The worst thing that can happen is the extractor is turned too hard causing it to break off inside the stuck bolt. This makes things even more complicated and should be avoided at all costs. If the bolt doesn’t turn right away with moderate force, don’t push the issue. Instead, use a torch to heat the end of the shaft surrounding the bolt threads.
The heat will help expand the shaft and will help loosen the stuck bolt. With any luck the broken bolt should come out without too much trouble.
Carefully examine the broken bolt. There is a good chance that the reason it broke in the first place will become clear. In this case the threads were full of dirt, which made it very hard to tighten the bolt. Regardless of what the problem was, it is never a bad idea to run a tap through the problematic hole to be certain it is free of debris and the threads are in good shape for the next bolt.
I hope you have found my documentation on removing broken bolts helpful. If you have a techniques or tips you want to share, a tool that makes the job easier, or anything else to add please leave a comment below!
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