EDGE-CUTTING 4T6566 - Caterpillar

Caterpillar Engines Equipped With A TurbochargerSome new turbocharger shaft and wheel assemblies use left handed threads to retain the compressor wheel on the shaft. The left handed threads can better resist the higher shaft torques of some newer engine ratings. The left hand threads can improve turbocharger reliability in severe service applications.
The illustration show both left (A) and right (B) hand threaded compressor wheel retaining nuts. Note the notches in the edges of the hex surfaces on the left hand threaded nut.
Compressor Wheel Retaining Nuts. Left Hand Threads (A). Right Hand Threads (B). Assembly procedures (thread preparation and torque) for left hand threaded nuts remain the same as those listed in the Service Manual Specification modules for right handed threads. It is very important to make turbocharger repairs immediately if a bearing system failure should occur. Timely repairs will help decrease the possibility of pressurized engine oil from getting into the intake or exhaust systems. Engine oil leaks into the intake or exhaust system can result in serious engine damage.