I got two cans of electric part cleaners and sprayed well the area around the piston rings and it was pretty clean using a shop vacuum at the same time. I re-oil the cylinder wall and lower it slowly, wipe and clean again. I even attached a straw to the tip of my shop vacuum nozzle and went around that area several times. I did this over and over and it is pretty clean. I taped all the water and oil holes before I did the cleaning. Also, don't you think all that carbon on top of the cylinder is abrasive? I work in the diesel fuel industry (test engineer) and I test diesel fuel injectors with abraisive material like Aluminum oxide (Alumina), lapping compound, and Arizona dust. I know what kind of damage they could do. Carbon is a solid and it is an abraisive too. I have done this job on BMW engines 3 times and haven't had any problems. I hope I am right and everything will be ok.
1993 190E 2.6
Advanced Diesel Systems Test and Research Engineer