Top end repair
Valve lash adjustment and secondary cam chain adjustment can be done with engine in chassis. Cam drive inspection and some part replacement can be done with the engine in chassis.
For all other top end repairs, the engine must be removed from the chassis. See 2.9 Engine replacement.
Bottom end repair
Bottom end repair can only be done with engine removed from chassis. See 2.9 Engine replacement.
Typical symptoms
Symptoms indicating a need for engine repair are often misleading, but generally if more than one symptom is present, possible causes can be narrowed down to make at least a partial diagnosis. An above normal consumption of oil, for example, could be caused by several mechanical faults. But when accompanied by a blue-gray smoke from the exhaust, and when low compression is present, it indicates the rings need replacing. Low compression by itself, however, indicates improperly seated valves, not worn rings.
Certain "knocking" noises may be caused by loose bearings, others by piston slap, a condition where piston or cylinder or both out of tolerance, allowing the piston to slap from front to rear of the cylinder as it moves up and down.
Most frequently, valves, rings, pins, bushings, and bearings need attention at about the same time. If the symptoms can be narrowed down through the process of elimination to indicate that any one of the above components is worn, it is best to give attention to all of the cylinder head and cylinder parts.