TM 5-3810-289-34
(5) Lift crankshaft from cylinder block, using
hooks covered with rubber hose, or a rope, to prevent
bearing surface damage, figure 3-218. Remove upper
main bearing shells.
(6) Tape lower and upper main bearing
shells together and identify according to cylinder number
for future reference.
b. Main Bearing Caps.
(1) Main bearing caps have an interference
fit to block of 0.002/0.004 in.
(2)
Caps must fit in block with no
perceptible clearance or "shake". Milled faces of cap
must always rest on mating portion of block to prevent
distortion during tightening.
(3) Replacement caps, must be machined
Figure 3-218. Lift crankshaft from block.
to fit.
c. Main Bearing Cap Replacement.
(3) A No. 7 new replacement cap does not
(1) Semi-finished replacement main bearing
have cap-to-block dowel holes and must be machined to
caps are available for limited use in rebuild shops.
block width.
Note. The responsibility for use of semi-finished
(4) Machine an equal amount of material
caps must be assumed by the engine owner or by the
from each end of semi-finished cap to provide
shop which performs the work.
0.002/0.004 in. interference fit in block.
(2) Replacement main bearing caps have
(5) If the cap is a rear cap (No. 7):
0.003 in. material in bore and 0.005 in. excess in length
(a) Remove locating dowels from block.
(pilot dimension). Other dimensions are the same as
(b) Locate and machine cap so thrust faces
finished main bearing caps.
of cap and block are flush. Use Prussion Blue on block
surface to locate dowel holes in cap.
(c) Remove cap.
(d) Drill dowel holes. Refer to figure 3-219.
(e) Reinstall cap and ream dowel holes to
the smallest permissible oversize.
(f) Install dowels in block.
(6) Install all caps on block and ream bore
as described in following paragraphs.
d. Inspection of Bearing Shells.
(1) Gage shell with ball point micrometer,
dial indicator thickness gage, or comparator. Refer to
(2) Discard shells that are worn more than
0.002 in. or if chipped, flaked, or scored. See table 2-2
Figure 3-216. Prying main bearing caps loose.
for thickness of standard shells.
(3)
Total worn maximum oil clearance
should not vary more than 0.002 in. between adjacent
main bearings. See table 2-2.
Caution: Under no circumstances should an
attempt be made to scrape bearing shells, or should
they be lapped or filed to increase oil clear(4) A
properly fitted bearing will appear dull gray after a
reasonable period of service, indicating it is running
on an oil film. Bright spots indicate metal to-metal
contact and black spots indicate excessive
clearance.
e. Crankshaft Thrust Rings.
(1) The best measurement of wear on
crankshaft thrust rings (half-rings) is the crankshaft end
Figure 3-217. Removal of main bearing caps from block.
clear-
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