As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
OUR ACFT DEPARTED WITH ONLY THE PILOT ON BOARD. THE ENG LOST PARTIAL POWER SO HE RETURNED. UPON INVESTIGATION CYLINDER 2 HAD NO COMPRESSION & WAS CRACKED HALF WAY AROUND THE CYLINDER HEAD. CYLINDER 4 WAS FOUND TO HAVE SOMEWHAT NORMAL COMPRESSION BUT DID INDICATE A LEAK & SMALL CYLINDER HEAD CRACK ALSO. IAW MFG TECH SERVICES, REPLACED ALL FOUR CYLINDERS WITH NEW MFG KITS.