Many years ago I had an R8 and the engine needed to be rebuilt. I decided to do it properly and knew that engine reconditioners at the time used a hot caustic bath to clean oil, gunk, paint and rust from the block. So I built a fire under a cut off 44 gallon drum (yes back in imperial days) and dropped the block into the water that had 1lb of caustic soda added per gallon. (About .5 kilo per 5 litres.) After bring it to the boil and let cool. Nice clean block but the aluminium plate had gone. Recently Cyber Papy bought up the subject on another web site. This is the modern version that uses a battery charger and electrolysis to remove rust and the caustic soda will remove paint any how. The rust takes about 2 or 3 hours depending on the current applied. The paint takes over 12 hours depending on its quality. Shortly I will show a photo of my set up. Perhaps CP will translate some of his notes from the French site.