4sfed wrote:Kevin Johnson wrote:
Right after this thread started I had a call from someone working on an alloy Porsche sump casting where a 5mm allen head bolt was stripped. The chemical method sounded perfect and I sent him a link.
It's an interesting method, so I set up an experiment. I dissolved 1.9 oz of alum in one cup of water and put an unplated 6mm stud and a scrap of aluminum in the solution. The solution has been maintained at 80° F for three days. The stud and aluminum are completely intact, although the aluminum is slightly discolored. I'll try a higher temperature, but that would make this method impractical to use on a head or block.
First, make sure to clean any oil or grease off of the bolt (yeah, I forgot to mention that before, sorry
). A good shot of brake clean should do it, then let it dry. Second, warming things up does two things, it speeds up the chemical reaction and it greatly increases the solubility of the alum. At 20C (68F) the solubility of potassium alum (Aluminium potassium sulfate dodecahydrate) is only 14 grams per 100 mL of water, but heating to just 50C (122F) raises this to 37 g per 100 mL water. That's over sixty percent by volume, and taking both temperature and concentration into account should speed things up over ten times. Barely cover the bolt with warm water, add enough alum to saturate the solution (so a little solid alum remains undissolved), and it will go much faster. Any kind of heater you can rig up will help. AvE used a christmas tree sized light bulb taped to his can in the video. If you have a incandescent worklight lay it as close as you can. An infrared heater would be great. I love chemistry but it can be painfully slow, as anyone who has waited hours and hours for Drano to clear a clog can testify. If what is broken off is soft and you can get in and drill, or get in a few whacks with a hammer, or any other mechanical method, do that first. If you broke off a good HSS or carbide drill or hardened screw extractor and drilling that is going to be a real pain, try this to at least loosen things up so you can pick out the hard bits after some hours of soaking. Or, if you have a very fragile piece or a very tiny bolt or other reason drilling is risky, try this. I haven't ever tried adding hydrogen peroxide so don't know how much that helps. If you try it, just use 3% peroxide instead of water to keep the concentrations high and the volume low.
