TUBE AS 2051751 - Caterpillar

Timing Aid Procedure
With Front Cover Removed (Exposing All Timing Marks)
Locations of timing marks (A), (B), (D), (E), tapped hole (C), and dowel rod (F).1. Pin time the flywheel. (Number 1 piston at TDC of its compression stroke.)2. Make sure timing mark (E) on the crankshaft gear is aligned with timing mark (D) on the cluster idler gear.3. Install the cam drive gear while aligning the timing mark (B) on the cam drive gear with the timing mark (A) at the top of the front housing. Tighten the bolts that hold the cam drive gear finger tight. The timing mark (B) on the cam drive gear may be up to 1/2tooth out of alignment with the cast mark (A) on in the timing gear housing.4. Remove the plug from the tapped hole (C).5. Insert a piece of 7.92 mm (.312 in) diameter dowel rod, or a 5/16inch bolt (F), with a minimum length of 76 mm (3 in) into the tapped hole (C). The dowel rod or bolt (F) should fit loosely (up to 3.5° movement of the gear, measured at the chopper teeth diameter) between the chopper teeth. (The chopper teeth are the reference for the speed timing sensor.) The dowel rod or bolt (F) will verify that the cam drive gear assembly in the correct position. Tighten the bolts that hold the cam drive gear in position.6. Remove the dowel rod or bolt (F). Install the plug in the tapped hole (C).7. Attempt timing calibration as shown in the Service Manual.With Only The Camshaft Gear Cover Removed (Exposing The Camshaft Gear And The Adjustable Idler Gear)
Follow this procedure ONLY IF YOU ARE CERTAIN that on one has changed the relationship between timing marks (D) and (E).1. Pin time the flywheel. (Number 1 piston at TDC of its compression stroke.)2. Check the alignment of timing marks (A) and (B). Reposition the camshaft gear if needed. Follow the Service Manual procedure.3. Attempt timing calibration as shown in the Service Manual.