(with new shells) exceeds 0.0045 inch or the main bearing journal-to-bearing shell clearance (with new shells)
exceeds 0.0040 inch, the crankshaft must be reground. Measurements of the crankshaft should be accurate to
the nearest O.0002 inch. Also, if the journal taper or the out-of-round is greater than 0.003 inch, the crankshaft
must be reground.
Also measure the crankshaft thrust surfaces (Fig. 8).
Inspection for Cracks
Carefully check the crankshaft for cracks which start at an oilhole and follow the journal surface at an angle of
45 to the axis. Any crankshaft with such cracks must be rejected. Several methods of determining the
presence of minute cracks not visible to the eye are outlined below.
Magnetic Particle Method: The part is magnetized and then covered with a fine magnetic powder or solution.
Flaws, such as cracks, form a small local magnet which causes the magnetic particles in the powder or solution
to gather there, effectively marking the crack. The crankshaft must be demagnetized after the test.
Fluorescent Magnetic Particle Method: This method is similar to the magnetic particle method, but is more
sensitive since it employs magnetic particles which are fluorescent and glow under black light. Very fine cracks
that may be missed under the first method, especially on discolored or dark surfaces, will be disclosed under
the black light.
Fluorescent Penetrant Method: This is a method which may be used on both nonmagnetic and magnetic
materials. A highly fluorescent, liquid penetrant is applied to the part. Then the excess penetrant is removed
from the surface and the part is dried. A developing powder is then applied which helps to draw the penetrant
out of the flaws by capillary action. Inspection is carried out under black light.
Nonfluorescent Penetrant Method: The test area being inspected is sprayed with Spotcheck or Dye Check.
Allow 1 to 30 minutes to dry. Remove the excess surface penetrant with clean cloths premoistened with
cleaner/ remover. DO NOT FLUSH SURFACE WITR CLEANER/REMOVER because this will impair
sensitivity. Repeat this procedure with additional wipings until residual surface penetrant has been removed.
Shake developer thoroughly until agitator rattles. Invert spray can and spray short bursts to clear valve. Then
spray this even developer film evenly over the test area being inspected. Allow developer film to dry
completely before inspecting. Recommended developing time is 5 to 15 minutes.
The above methods provide basic instructions. Specific details should be obtained from the supplier of the
equipment or material.
A majority of indications revealed by the above inspection methods are normal and harmless and only in a
small percentage of cases is reliability of the part impaired when indications are found. Since inspection
reveals the harmless indications with the same intensity as the harmful ones, detection of the indications is but
a first step in the procedure.
Interpretation of the indications is the most important step.
All Detroit Diesel crankshafts are magnetic particle inspected after manufacture to ensure against any shafts
with harmful indications getting into the original equipment or factory parts stock.