Download INITIAL CHECKS (PRIOR TO REMOVAL) PURPOSE Checking and recording the ignition timing and manifold vacuum level before and after the timing belt replacement allows for two assurances: – Initial conditions are correct. – Verifies the quality of the job after the belt has been installed. WHY Ignition Timing Ignition timing is the position of the piston on its compression stroke when the ignition coil fires the associated sparkplug. Ignition timing is affected by two sources. – Physical rotation of the distributor. – Alignment of the camshaft and crankshaft via the timing belt. Prior to replacing the timing belt it is very important to verify that this relationship is correct. If the timing belt is installed correctly the after-repairs timing check should be within 2 degrees of the pre-repairs timing check. NOTE: Minor differences, +/- 2 degrees may result from original belt stretching as it aged. If the timing belt is initially installed incorrectly, the prerepairs ignition timing may not be correct, and the after-repairs timing will differ greatly from the initial. Checking the timing before and after the job will help prevent confusion and verify the job was done correctly.