01-16
Basic Engine
01-16
CLEANING AND INSPECTION (Continued)
Pistons, Pins and Rings
Main and Connecting Rod Bearings
Cleaning
Cleaning
Remove deposits from the piston surfaces. Clean gum or
varnish from the piston skirt, piston pins and rings with
solvent.
Do not use a caustic cleaning solution or a wire
brush to clean pistons.
Clean the bearing inserts and caps thoroughly in solvent,
and dry them with compressed air.
Do not scrape gum or
varnish deposits from the bearing shells.
Clean the ring grooves with a ring groove cleaner. Make
sure the oil ring slots (or holes) are clean.
CLEANER
Inspection
Carefully inspect the pistons for fractures at the ring lands,
skirts and pin bosses, and for scuffed, rough or scored
skirts. If the lower inner portion of the ring grooves has a
high step, replace the piston. The step will interfere with
ring operation and cause excessive ring side clearance.
Spongy, eroded areas near the edge of the top of the
piston are usually caused by detonation or pre-ignition. A
shiny surface on the thrust surface of the piston, offset from
the centerline between the piston pin holes, can be caused
by a bent connecting rod. Replace pistons that show signs
of excessive wear, wavy ring lands or fractures or damage
from detonation or pre-ignition.
Check the piston to cylinder bore clearance by measuring
the piston and bore diameters. Refer to the specifications
for the proper clearance. Refer to Cylinder Block Inspection
for the bore measurement procedure.
Measure the OD of
the piston with micrometers approximately 57.2 mm
(2-l/4 inches) below the dome and at 90 degrees to the
piston pin bore.
Check the ring side clearance.
Replace piston pins showing signs of fracture, etching or
wear. Check the piston pin fit in the piston and rod. Refer to
Piston and Connecting Rod Assembly.
Check the OD of the piston pin and the ID of the pin bore in
the piston. Replace any piston pin or piston that is not
within specifications.
Replace all rings that are scored, broken, chipped or
cracked. Check the end gap and side clearance.
Rings
should not be transferred from one piston to another
regardless of mileage or hours.
SECTIONS
FATIGUE FAILURE
MPROPER SEATING
SCRATCHES
WlPED OUT
DIRT IMBEDDED
INTO BEARING MATERIAL
SCRATCHED BY DIRT
LACK OF OIL
OR MWROPER
CLEARANCE
lc?izzil
FROM ENTIRE SURFACE
TAPERED JOURNAL
OR CRANKSHAFT-
RADIUS RIDE
(HOURGLASSING)
A100951A
Inspection
Inspect each bearing carefully. Bearings that have a
scored, chipped, or worn surface should be replaced. The
copper lead bearing base may be visible through the
bearing overlay. This does not mean that the bearing is
worn. It is not necessary to replace the bearing if the
bearing clearance is within recommended limits. Check the
clearance of bearings that appear to be satisfactory with
Plastigage as detailed under Overhaul - Main and
Connecting Rod Bearings.
Cylinder Block
Cleaning
After any cylinder bore repair operation, such as honing or
deglazing, clean the bore(s) with soap or detergent and
water. Then, thoroughly rinse the bore(s) with clean water
to remove the soap or detergent, and wipe the bore(s) dry
with a clean, lint-free cloth. Finally wipe the bore(s) with a
clean cloth dipped in engine oil. If these procedures are not
followed, rusting of the cylinder bore(s) may occur.
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