Timing marks appear on the flywheel and are used to set and adjust the timing of the ignition. In most fully electronic ignitions, the timing takes place at top dead center, or TDC. In motorcycles, twin-style long block engines feature three timing marks: front cylinder, rear cylinder and front piston.
Identify timing marks in a twin-style long-block motorcycle engine by location and markings. The front firing mark is 35 degrees before TDC and features a vertical line in the middle of the hole. The rear firing mark is 35 degrees before TDC, with a dot in the middle of the hole. The front piston at TDC has a colon in the middle of the hole.