Doosan G643, Руководство по обслуживанию

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G643 (E) Service Manual Chapter 3. Engine Mechanical System 91
Crankshaft Bearings
Figures 12-61 through 12-63
Cleaning and Inspection
Clean
• Crankshaft with solvent.
- Do not scratch the bearing journals.
- Remove all sludge from the oil passages with
compressed air.
• Crankshaft bearing.
- Wipe free of oil with a soft cloth.
Inspect
• Crankshaft for cracks.
- Use the magnaflux method if available.
- Crankshaft, crankshaft bearing journals, and
thrust surfaces for scoring, nicks or damage
caused by lack of lubrication.
- Main bearing inserts for scoring or other
damage. In general, the lower crankshaft
bearings (except the #1 bearing) show the
greatest wear and distress from fatigue. Upon
inspection, if a lower crankshaft bearing is
suitable for reuse, it can be assumed that the
upper crankshaft bearing is also satisfactory. If
a lower bearing shows evidence of wear or
damage, both the upper and lower crankshaft
bearings must be replaced.
Measuring Bearing Clearance
Crankshaft bearings are of the precision insert type
and do not use shims for adjustment. If clearances
are excessive, new upper and lower bearings will be
required. Service bearings are available in standard
size and undersize.
Selective fitting of crankshaft bearings is necessary
in production to obtain close tolerances. For
example, you may find one-half of a standard
crankshaft bearing with one-half of an undersize
crankshaft bearing.
To determine the correct replacement bearing size,
the bearing clearance must be measured accurately.
Either of the following two methods may be used,
however, the micrometer method gives more reliable
results and is preferred.
Micrometer Method
Measure
1 . The crankshaft journal diameter with a
micrometer in several places, approximately 90°
apart. Average the measurements.
2
. Compute taper and runout. Refer to “Specifi-
cations” for allowable limits.
Install or Connect
3 . Crankshaft bearings into the crankshaft cap and
engine block.
4
. Install crankshaft caps and bolts.
5.
Tighten bolts to specification.
Measure
6 . Bearing inside diameter (I.D.) using an inside
micrometer.
7
. Compare crankshaft bearing clearance with
“Specifications”.
8
. If bearing clearances exceed specification, install
new crankshaft bearings.
A . Measure inside diameter with an inside
micrometer at 90° to the split line of the
crankshaft bearing.
B . Subtract journal diameter from bearing inside
diameter to obtain bearing clearance. Refer to
“Specifications” for bearing inside clearance.
Replace or repair the crankshaft if clearance
exceeds specification.
Figure 12-61 Measuring Crankshaft Journals