190e2.3 - rebuilt engine installed & blew valves

From an initial discovery of oil in the radiator, I have progressed to numerous expensive and time consuming problems. I am not a mechanic but certainly wish I were! Apparently due to serious overheating prior to my buying this 1993 model car, I have now had (in brief) the head milled, the head gasket replaced and when that resulted in no compression in one cylinder out of four, the engine has now been rebuilt. Only problem is when the rebuilt engine was installed, four valves blew out. I have been told perhaps because both were milled they did not mesh properly causing this problem. The engine has been returned to the rebuilder. I don't know much about this type of situation except the ongoing expense without solving the problem, i.e. I cannot drive the car! We do not have Mercedes specialists here and this work is being done by well reputed mechanics but I have been told all the settings, adjustments are tricky. Is this going to require a Mercedes specialist to put this thing back together? Your opinions?

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Never heard of BLOWING valves. Bending them due to over-revving is another story. Sounds like the rebuilder doesn't know about valve installed height. Very critical with hydraulic lifters. Engines that have been overheated several times aren't good for much of anything. Aluminum (cylinder head) doesn't respond to this very well. Might be better to look for 1992-93 used engine.