Performed 100 hour inspection on ENGINE. Compression: #1 75/80, #2 75/80, #3 72/80, #4 70/80. Drained oil and serviced with 7qts. Phillips 66 100AW oil. Replaced oil filter CH48111-1, cut open old filter and inspected, no metal found. Replaced spark plugs P/N REM40E (QTY 8). Tightened and adjusted 4 oil return hoses. Checked MAG timing. Adjusted exhaust shroud. Work performed in reference to Cessna 172M MM, and IPC. I certify that this ENGINE was inspected in reference with Cessna's 172M 100-hour inspection checklist and was determined to be in an airworthy condition. Aircraft returned to service.