Center punch, dead center of sheered bolt. Use new small drill bit 3-4mm and drill dead center all the way through bolt, keeping drill perfectly square at all times. Take your time an go slow. Your drill should be on high speed. Lubricate as you are drilling with soluble oil or wd40. DO NOT BREAK DRILL BIT IN HOLE. Take your time it wont be easy. Change drill bit if needed. If no swarf is coming away renew drill bit. Eventually you will get through the bolt. Go to an engineering shop and purchase an easy out kit. These will screw into a hole on a left hand thread to remove the bolt. Each easy out requires a certain size hole to screw into. You will then have to re drill your small hole to this size. If the bolt you are trying to remove is large you will need to use a large easy out. Do not use a small easy out on a large bolt it will be futile. You will need a tap wrench to hold your easy out. Do not sheer the easy out in the hole if it looks like it is not going to happen it probably wont. Now you are going to have enlarge your perfectly centered hole up a millimeter at a time until you can almost see the the threads, then you will require a tap set and start to try and clean up your threads. On your tap and die set it will tell you what size hole you need to drill. Start with a taper tab and use it with wd40 one turn in and half a turn out (this is to snap off the swarf otherwise it will rip your threads). When this eventually bottoms out remove it and use an intermediate tap in the same manner with wd40. When this bottoms out you require to do it again with the plugging tap. Remove all tools wash out threads, inspect throughly if they are good and clean insert new correct bolt for the job. Do not use any old bolt they all have different strength ratings. If the threads are poor you will need to use a helicoil kit. This is a similar process but you will drill all your bad threads away re tap and insert a spring into the hole with a special tool. If you can remove your damaged component and take it to an engineering firm (preferably automotive) and they will do the whole job for you without you having to get a lot of expensive kit. They may use a technique called sparking it out (dont worry about the detail) these boys do it day in and day out. It should not cost you more than £40- £50. If you decide to have a go yourself spend as much as you can afford on good tools it will pay for itself in the long run. If you are having a go and snap a drill bit in the bolt do not try to drill it out you will only snap another. Try to get broken bit out with needle nosed pliers small screwdriver, compressed air anything you have got to hand. If you cant get it out remove component and take it to an engineering firm and tell them what has happened, they will sort it out. If you get to the end of the process and it has all failed, remove the component and take it to an engineering firm. If you decide to take it to a local garage and thy ball it up they will send it to an engineering firm and you will have to pay two bills. Hope this helps. It all sounds long winded but it is easy really. Have fun and dont snap any drill bits
