What was found
(CAN) PILOT REPORTED THE ENGINE RUNNING ROUGH DURING TEST FLIGHT, AFTER CYLINDER CHANGE. POST-FLIGHT COMPRESSION TEST FOUND DIFFERENTIAL PRESSURE 0/80, WITH THE INTAKE VALVE OPEN. INSPECTION FOUND THE INTAKE PUSH ROD TO BE THE WRONG LENGTH, SHORTER PUSH ROD INSTALLED AND THE COMPRESSION CHECK INDICATED 75/80. THE SUBMITTER SUGGESTS THAT INTAKE AND EXHAUST PUSH RODS, WHICH ARE DIFFERENT LENGTHS, ARE SOME TIMES INSTALLED INCORRECTLY.