Turbocharger Internal Inspection

Fig. 2 Journal bearing clearance check:

1. Remove the turbocharger assembly but do not separate the center housing rotating assembly from the turbine housing.
2. Manually operate the wastegate linkage and using a small mirror, observe wastegate movement in the elbow assembly. Replace the elbow assembly if the wastegate fails to open or close.
3. Check for loose backplate to center housing rotating assembly bolts and tighten, if necessary.
4. Spin the compressor wheel. If rotating assembly binds or drags, replace the center housing rotating assembly.
5. Inspect center rotating housing assembly for sludge in the oil drain area. Clean, if minor, or replace center housing rotating assembly if excessively sludged or coked.
6. Inspect compressor oil seal for damage or leakage on the compressor wheel side of the backplate. Replace center housing rotating assembly if oil seal damage or leakage is present.
7. If compressor wheel is damaged or severely coked, replace center housing rotating assembly.
8. If center housing rotating assembly is being replaced, pre-lubricate with engine oil.
9. Inspect compressor housing and turbine housing. If either housing is gouged, nicked or distorted, replace as necessary.
10. Remove turbine housing from center housing rotating assembly.
11. Check journal bearing radial clearance as follows:
a. Attach a rack and pinion type dial indicator (Starrett model 656-517 or equivalent with a two inch long, 3/4 to 1 inch offset extension rod) to the center housing so the indicator plunger extends through the oil output port and contacts the turbine wheel assembly shaft, Fig. 2. If required, a dial indicator mounting adapter can be utilized, Fig. 2.
b. Manually apply pressure equally and at the same time to both the compressor wheel and turbine wheel as required to move the turbine wheel assembly shaft away from the dial indicator as far as possible.
c. Zero the dial indicator.
d. Manually apply pressure equally and at the same time to both the compressor and turbine wheels as required to move the turbine wheel assembly shaft toward the dial indicator plunger as far as possible. Note maximum reading on dial indicator. To ensure that the dial indicator reading is the maximum obtainable, roll the wheels slightly in both directions while applying pressure.
e. Manually apply pressure equally and at the same time to both the compressor and turbine wheels as required to move the turbine wheel assembly shaft away from the dial indicator as far as possible. The dial indicator should return to zero.
f. Repeat steps 2 through 5 as required to ensure the maximum clearance between the center housing bores and the shaft bearing diameters, as indicated by the maximum shaft travel, has been obtained.
g. If the maximum bearing radial clearance is less than .003 inch or greater than .006 inch, replace the center housing rotating assembly. Continued operation of a turbocharger having excessive bearing radial clearance will result in severe damage to the compressor and turbine wheels and the housings.

Fig. 3 Thrust bearing clearance check:

12. Check thrust bearing axial clearance as follows:
a. Mount a dial indicator (Starrett model 25-141 or equivalent) at the turbine end of the turbocharger so the dial indicator plunger contacts the end of the turbine wheel assembly, Fig. 3.
b. Manually move the compressor wheel and turbine wheel assembly in each direction shown on the indicator dial.
c. Repeat previous step to ensure the maximum clearance between the thrust bearing components, as indicated by the maximum turbine wheel assembly travel, has been obtained.
d. If the maximum thrust bearing axial clearance is less than .001 inch or greater than .003 inch, replace the center housing rotating assembly. Continued operation of a turbocharger having excessive thrust bearing axial clearance will result in severe damage to the compressor and turbine wheels and the housings.