RE: dz160 stop in Loud noise
As Petec states, you may have done damage, bent valves are the most common, you may have put half moon circles on top of the piston as well.
The circles on top of the piston are ok, but check the valve stems for straightness. But also be aware that piston damage etc is also possable,
strip it down and inspect.
I don't know what Petec and others do in the US, but I prefere the pinch method of determining the max rpm of the 160, there should be a previous thread somewhere
about this method.
YS Servive Down Under