MILEAGE ISNT THE ONLY FACTOR TO CONSIDER WHEN REPLACING THE TIMING CHAIN. FIRST OF ALL THE TIMING CHAIN TENSIONER IS THE KEY TO LONG LIFE OF THE CHAIN. SECOND IS FREQUENCY OF OIL CHANGES. BUT THE BEST WAY TO DETERMINE IF THE CHAIN NEEDS REPLACEMENT IS TO REMOVE THE VALVE COVERS & ALIGN TIMING MARKS ON CAMSHAFTS THEN LOOK AT CRANKSHAFT POSITION TO DETERMINE STRETCH IN DEGREES . NORMALLY 125K. MILES IS A STARTING POINT!