BROKEN SCREWS & BOLTS
If the screw or bolt is flush with the case and you can't grab it, soak it with WD or other penetrating agent. Drill the appropriate size hole for the correct size easy out - DEAD CENTER. I like to drill all the way thru the bolt so you can get WD behind it and not bottom out the easy out. You have to use an easy out that will not catch the aluminum. Use a T-type tap handle to apply equal pressure on the easy out. A crescent wrench will apply unequal pressure and possibly break it. If this doesn't work fairly easy use the following method.
Get everything ready to go and then slowly heat the casing around the bolt with a propane torch, but not next to the bolt. The idea is to expand the aluminum and not heat the steel. Aluminum expands at 7 times the rate of steel, so you have to be quick before the steel heats up too. If it does, stop and let it cool, soak it and try again.
Sometimes you can use a left-thread tap, but they can be hard to find.
Moped Army in no way is affiliated with these methods and should not be held accountable for the negligence of an individual who has not had proper training of handling hazardous chemicals**USE AT YOUR OWN RISK!!!
Nitric Acid: The fastest, though risky, method of removing a stud, bolt, or broken tap from an ALUMINUM cylinder is to use Nitric Acid. Though this product may seem hard to get your hands on, you can usually get some from your local universities chem lab or online from time to time. Build a clay bowl around your steel nemesis and pour in the acid and watch your bolt melt away. Use in a well ventilated area away from other metal because the fumes alone are known to rust other metals in the area. Use proper breathing, hand, and eye protection because this stuff is extremely potent and will eat your skin.
Alum Powder: Another method with virtually no risk is to use a product by the name of ALUM. It can be found on the spice isle of most any grocery store and is used in the packaging of pickles to give them more *snap. This is a very slow but effective way...here is the method of use: heat up a large pot of water to almost a boil (you do not need a full pot of water) insert a plastic bucket into the pot and fill it with enough water to cover your ALUMINUM cylinder. Once the bucket water is hot...pour your ALUM into the water until the water can no longer break down the powder and the water is very murky. insert your cylinder and let it sit. You will see tiny bubbles coming from the area where your bolt is and this is showing that the ALUM is attacking the steel. Check on your cylinder from time to time and if the water gets low add more. With the right consistency you can have your bolt out in 3-12 hours. Yes, this is a long time but sometime, especially taps, they simply cannot be drilled out due to their strength. A packet of Alum will cost between $1-2 and you will need about 5-10 ounces depending on the job. Again, this is a slow process but is better than paying $50-100 for someone to blast it with their EDM. Cleanup is pretty sticky but with some soap, water and an old toothbrush you're good to go. Good luck.