TRANSMISSION AR 1957891 - Caterpillar

probable root causes are listed below:
Faulty accessory
Damage to valve train components
Failure of connecting rod bearing
Crankshaft bearingsPerform the following checks:
Isolate the source of the noise. Remove the suspect engine accessories. Inspect the suspect engine accessories. Repair the engine accessories and/or replace the engine accessories.
Remove the valve cover from the suspect cylinder(s). Check the following items for damage: camshaft, valve rotocoil, valve springs, roller followers (rocker arm), rocker shaft, bridges and injectors. Check for valves that do not move freely. Remove the cylinder head and inspect the valves. Replace any damaged parts. If damage has occurred, ensure that the following components are free of contamination: cylinder liner, piston and exhaust system. Replace any damaged parts.
Inspect the connecting rod bearings and the bearing surfaces (journals) on the crankshaft. Check the piston pin for excessive wear. Replace any damaged parts.
Check main journals of the crankshaft and the main journal bearings for excessive wear. Replace any damaged parts.