Bolts break for one of several reasons:
Excessive tension- the bolt is subjected to excessive length-wise pulling force and is pulled apart. Fracturing of the metal of the bolt due to repeated loading and unloading can exacerbate this effect.
Shearing/bending- excessive side loading, especially of an under-tightened fastener.
The likely one in this case, excessive torque/twisting force which separates the bolt across its structure. A common reason for this effect is the use of excessive torque in the attempt to free seized threads which resist turning such that the fastener fails across the weakest are of unsupported structure.
Easy-outs and other devices intended to assist in removal are seldom applicable in this case although many stories of tragedy begin with their attempted use.
Let's look at this problem in the light of two simple possibilities:
1) The bolt was over tightened, sheared off, etc. but the threads of the remaining portion of the bolt are not seized to the surrounding structure. In this case, the remaining threaded portion of the bolt is relatively free to rotate within the threads, allowing a low torque/twisting force to easily thread the broken portion out of the head. In this case, drilling the broken portion or even cutting a screwdriver slot should allow the broken piece to be screwed out. No big deal.
2) The bolt's threads were seized into the cylinder threads such that the bolt's body was unable to withstand the torque applied in the attempt to screw the bolt out. In this case, drilling the bolt in order to drive in a smaller diameter easy-out cannot be reasonably expected to provide sufficient torque resistance to allow the seized portion to be forced to turn. Not rocket science, right? So why do people routinely drill a small hole, drive in a tiny easy-out and expect to rip loose the bigger bolt?
Beats me too!
One of the best means of dealing with such a seizure is often to arc weld a nut onto the end of the broken piece and to use this as a means of working the piece loose. The welding causes extremely rapid heating & expansion of the broken piece which will cause the steel to attempt to expand with great effort. Since the surrounding structure will not allow the steel stud to expand and the steel is well into the red/yellow temperature range, the steel has become plastic. The expansion force causes such high pressure within the steel that it will yield axially (length-wise) and flow so that the stud becomes longer but thinner.
When the stud cools, it contracts away from the surrounding material because there is less steel in the cross section and so the thread clearance becomes greater, releasing the stud.
If you are unable to accomplish this and are forced to another solution, drilling the piece, in whole or in part is a popular means of removal. Left hand drill bits combined (not rocket science I know but it may not surprise you to hear that some people don't work out that left hand drill bits require the use of a left hand/reverse rotation drill) with a left hand drill work well because of the torque applied in drilling having the effect of attempting to turn the piece out rather than inward.
Start by accurately centre punching the end of the broken piece to be drilled. The punch mark will be the beginning of the drilling so must be very accurately in the exact centre of the bolt!
Next, use a small bit to begin drilling and reinspect the hole to ensure that you are drilling on centre! Don't make any mistakes with this as it is critical. I have removed at least hundreds/likely thousands of broken fasteners so know of which I speak.
Some prefer to pilot drill/use a smaller diameter drill to drill through the length of the stud first and then to drill to just under the thread root diameter. A small minority drill to that size with one drilling but I am not one of those. Regardless, make no mistake that the drilling must be concentric to the stud!
If you drill off centre, you will be unable to drill to the full root diameter of the stud and will be self-inseminated if the piece cannot be turned by a easy-out. Don't go there as dealing with that is a really puddle of pus.
If you start on centre and drill off the concentric line of the stud, you will drill through the wall of the stud into the cylinder threads. This will be fun because the piece will be locked into place such that it will never turn. Don't go there! Nasty to deal with!
Drill straight down the centre of the broken stud, all the way through the full length, and gradually increase the size of the drill bit until you have reached just smaller sizing to the root diameter of the threads. Then try a tapered easy out to see if the piece will thread out.
If not, tap the easy out from the stud and heat the tube of remaining material rapidly with an oxy torch to see if it will free due to the plastic effect to which I referred earlier.
If necessary, drill out to the root of the threads and then pick and remove the remaining threads.
If you drill off centre or out of the body of the broken stud, you will find out how dentists make the big bucks! I have removed hundreds of these because it remains illegal to hunt down and execute idiots. Yep, still illegal although I do check with the local police from time to time.:lol:
In the case of having drilled off centre, the remaining portion will need to be cut into segments which can be removed, piece by piece. I use a small die grinder and tiny dental-sized burrs but the cost of doing this is not modest for two reasons: the time and cost of the tools; the desire to punish the idiot. Do I sound bitter?
Someone mentioned doing some trial runs and no one should fail to heed this advise. I should have been typed in capitals and large font as he knows of which he speaks! I used to force apprentices to do broken fastener extractions over and over until they were near rebellion but later, they always thanked me.
Go slow, think twice and take care. Use drilling lube!
Hope I didn't miss something which could help. If you were in the Upper Fraser Valley of Canada's Wet Coast, you could bring it over and I'll gladly help. It would only cost you a 40 oz of Wisser's rye. I find that drinking some before starting really improves my confidence!
HIH
Norm
....any suggestions? I circled the location on the cylinder block were the bolt is broken off ..thanks!
