engine problems

hi all, need some pointers....

have just rebuilt a 12j lump, after piston no 2 decided to drop its bottom half into the sump
so new pistons, big ends, head (was badly pitted), injectors, valves, springs etc etc etc..... later and its back together and running......

this morning the guy phones me to say he has suffered a loud "thumping" noise and a loss of power, accompanied by some black smoke (over fuelling?)
any ideas what could be the problem, the thumping has now gone and it is running ok again......

cheers all

Tell him that is 'normal' that is what the stealers do. If the problem has gone away, it is best to ignore it.