Detroit Diesel 4000 Series, Service Manual, Page: 402 / 2706

SERIES 4000 12/16V SERVICE MANUAL
Thermal Cracks
Review the following comments on thermal cracks:
1. A characteristic of thermal cracks (arrows) is that they are almost always parallel to the
axis of the component. See Figure 182.
Figure 182 Thermal Cracks on Crankshaft
2. Transverse cracks sometimes come out from these cracks.
3. Heavy thermal cracks are approximately as deep as the thickness of the hardness layer.
4. Replace crankshaft with such cracks.
5. Crankshafts exhibiting minor thermal cracks can be repaired, providing that regrinding to
a repair stage or local grinding will remove the damage.
6. Carefully regrind the affected bearing journals, according to crack depth, to a permissible
repair size.
7. Minor cracks can also be repaired by local grinding.
8. Carry out preliminary grinding before the after-curing, otherwise the thermal cracks
could increase in length and depth.
9. Grind to specified repair stage only after bearing journals have been hardened.
Cracks Caused by Grinding
Review the following comments on cracks caused by grinding:
All information subject to change without notice.
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