TM 5-3810-300-24&P-3
1.3 Crankshaft
journal. If the ridges are greater than .0005", first use
Crankshaft Measurements
120 grit emery cloth to clean up the ridge, 240 grit emery
cloth for finishing and wet crocus cloth for polishing. Use
Support the crankshaft on its front and rear journals on
of a piece of rawhide or other suitable rope wrapped
V-blocks or in a lathe and check the alignment at the
around the emery cloth or crocus cloth and drawn back
adjacent intermediate main journals with a dial indicator.
and forth will minimize the possibility of an out-of-round
condition developing (keep the strands of rawhide apart
When the runout on the adjacent journals is in opposite
to avoid bind). If rawhide or rope is not used, the
directions, the sum must not exceed .003" total indicator
crankshaft should be rotated at intervals. If the ridges
reading. When the runout on the adjacent journals of the
are greater than .001", the crankshaft may have to be
four and six cylinder crankshaft is in the same direction,
reground.
the difference must not exceed .003" total indicator
reading. If the runout limit is greater than given in Table
Carefully inspect the rear end of the crankshaft in the
1, the crankshaft must be replaced.
area of the oil seal contact surface for evidence of a
rough or grooved condition. Any imperfections of the oil
Measure all of the main and connecting rod bearing
seal contact surface will result in oil leakage at this point.
journals (Fig. 6). Measure the journals at several places
on the circumference so that taper, out-of-round and
Slight ridges on the crankshaft oil seal contact surface
bearing clearances can be determined. If the crankshaft
may be cleaned up with emery cloth and crocus cloth in
is worn so that the maximum journal-to-bearing shell
the same manner as detailed for the crankshaft journals.
clearance (with new shells) exceeds .0044", the
If the crankshaft cannot be cleaned up satisfactorily, the
crankshaft must be reground. Measurements of the
oil seal may be repositioned in the flywheel housing as
crankshaft should be accurate to the nearest .0002".
outlined in Section 1.3.2.
Also, if the journal taper of a used crankshaft exceeds
.0015" or the out-of-round is greater than .001", the
Check the crankshaft thrust surfaces for excessive wear
crankshaft must be reground.
or grooving. If only slightly worn, the surfaces may be
dressed with a stone. Otherwise it will be necessary to
Also measure the crankshaft thrust surfaces (Fig. 8).
regrind the thrust surfaces.
Inspection for Cracks
Check the oil pump drive gear and the crankshaft timing
gear for worn or chipped teeth. Replace the gears, if
Carefully check the crankshaft for cracks which start at
necessary.
an oil hole and follow the journal surface at an angle of
45 to the axis. Any crankshaft with such cracks must be
Check the crankshaft dowel extension. Current dowels
rejected. Several methods of determining the presence
extend 1/2" from the crankshaft while former dowels
of minute cracks not visible to the eye are outlined below.
extend 5/8".
Inspect the crankshaft for cracks as outlined under
Inspection for Cracks.
CRANKSHAFT RUNOUT
Max. Runout
Engine
Journals
(Total indicator
reading)
6-71
At No. 2 and No. 6
.002"
At No. 3 and No. 5
.004"
At No. 4
.006"
TABLE 1
Fig. 4. Critical Crankshaft Loading Zones
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