ACR = Automatic Compression Release
First you need the adjust the valves and while adjusting turn the engine through a couple revs you should notice the lower rocker (intake valve) open slightly as approach TDC compression stroke and reclose (bump as it is called). If not present after the vavles are adjusted then it a tear down of the engine to remove the broken parts and install a new camshaft along with a possible governor/oil slinger. Of course you replace the crankcase gasket and the PTO side oil seal while you are at it.