The seven-step inspection procedure outlined here was adapted, with modifications, from material supplied by John Deere.
1. Turbo housing Before disconnecting the oil lines, examine external surfaces of the housing for oil leaks, which would almost certainly mean turbo seal failure.
2. Compressor housing inlet and wheel Inspect the compressor wheel for erosion and impact damage. Erosion comes about because of dust intrusion; impact damage is prima facie evidence of negligence. Carefully examine the housing ID and compressor blade tips for evidence of rubbing contact, which means bearing failure.
3. Compressor housing outlet Check the compressor outlet for dirt, oil, and carbon accumulations. Dirt points to a filtration failure; oil suggests seal failure, although other possibilities exist, such as clogged turbo-oil return line or crankcase breather. Carbon on the compressor wheel might suggest some sort of combustion abnormality, but the phenomenon is also seen on healthy engines. I can only speculate about the cause.
4. Turbine housing inlet Inspect the inlet ports for oil, heavy carbon deposits, and erosion. Any of these symptoms suggest an engine malfunction.
5. Turbine housing outlet and wheel Examine the blades for impact damage. Look for evidence of rubbing contact between the turbine wheel and the housing, which would indicate bearing failure.
6. Oil return port The shaft is visible on most turbochargers from the oil return port. Excessive bluing or coking suggests lubrication failure, quite possibly caused by hot shutdowns.
7. Bearing play measurements Experienced mechanics determine bearing condition by feel, but use of a dial indicator gives more reliable results. Note that measurement of radial, or side-to-side, bearing clearance involves moving the shaft from one travel extreme to another, 180° away (Fig. 9-8A). Hold the shaft level during this operation, because a rocking motion would muddy the results. Axial motion is measured as travel between shaft thrust faces (Fig. 9-8B). In very general terms, subject to correction by factory data for the unit in question, we would be comfortable with 0.002 in. radial and 0.003 in. axial play. Note that Schwitzer and small foreign types tend to be set up tighter.