Most are due to failure within the power assembly itself such as a dropped valve, broken piston or internal coolant leak.
Less common are replacements to repair catastrophic failures such as broken connecting rods or a "hydro-locked" power assembly that has been broken or knocked out of the cylinder block when the cylinder filled with coolant during engine operation and the inability of the piston to compress the liquid caused catastrophic failure.
The use of a fiber optic endoscope (flexible borescope) may facilitate this inspection and evaluation, but this is not a requirement, nor is it a part of EMD's maintenance program.
A proper inspection requires filling and pressurizing the cooling system to check for leakage from the power assemblies.
The preferred tool for engine rotation is an electrically powered, hydraulically operated "turning jack".
The turning jack uses a hydraulic cylinder and ram assembly that automatically advances to engage a hole in the flywheel.
Not only is a turning jack faster and more efficient, it is also safer since there is no risk of a barring lever coming loose and causing injury or damage.
Also, with a turning jack, there is no need for the mechanic to be in physical contact with the engine at any point during the inspection process.
Rocker arm rollers can be inspected for proper rotation, potential valvetrain problems such as insufficient or excessive clearance can be observed, piston ring movement in the ring grooves indicating excessive groove wear can be observed, broken valvesprings can be more easily seen, and so on.
Although the components are large and heavy and specialized tools are required, the replacement process is straightforward and simple.