Inspect the ring gear for worn, chipped, or cracked
teeth If the teeth are damaged. replace the ring gear.
skirts and pin bosses, and for scuffed. rough or scored
With the flywheel installed on the crankshaft. check
ski, If the lower inner portion of the ring grooves has a
the flywheel face runout, following the procedure under
high step. replace the piston. The step will interfere with
Diagnosis and Testing.
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
Remove the bearings from the rod and cap. Identify the
from the centerline between the piston pin holes. can he
caused by a bent connecting rod. Replace pistons that
bearings if they are to be used again. Clean the
show signs of excessive wear, wavy ring lands or
connecting rod in solvent. including the rod bore and the
fractures or damage from detonation or pre-ignition.
back of the inserts. Do not use a caustic cleaning solution.
Check the piston to cylinder bore clearance by measuring
Blow out all passages with compressed air.
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 connecting rods and related parts should be carefully
inspected and checked for conformance to specifications.
2'/4 inches below the dome and at 90 degrees to the
Various forms of engine wear caused by these parts can
piston pin bore. Check the ring side clearance following
the procedure under Fitting Piston Rings in this section.
be readily Identified.
Replace piston pins showing signs of fracture,
A shiny surface on either pin boss side of the piston
etching or wear. Check the piston pin fit in the piston and
usually indicates that a connecting rod is bent.
rod. Refer to Piston and Connecting Rod Assembly.
Abnormal connecting rod bearing wear can be
Check the ()D of the piston pin and the ID of the pin
caused by either a bent connecting rod. worn or damaged
bore in the piston. Replace any piston pin or piston that is
crank pin. or a tapered connecting rod bore.
not within specifications.
Twisted connecting rods will not create an easily
Replace all rings Check the end gap and side
identifiable wear pattern. but badly twisted rods will,
disturb the action of the entire piston. rings, and
Rings should not be transferred from one piston to
connecting rod assembly and may be the cause of
another regardless of mileage or hours.
excessive oil consumption Inspect the connecting rods for
MAIN AND CONNECTING ROD BEARINGS
signs of fractures and the bearing bores for out-of-round
and taper. If the bore exceeds the recommended limits
Clean the bearing inserts and caps thoroughly In solvent.
and/or if the connecting rod is fractured, it should be
and dry them with compressed air. Do not scrape gum
replaced. Check the I D of the connecting rod piston pin
or varnish deposits from bearing shells.
bore. If the pin bore In the connecting rod is larger than
specifications. install a 0.002 inch oversize piston pin.
First, prefit the oversize piston pin to the piston pin bore
Inspect each bearing carefully. Bearings that have a
by reaming or honing the piston. Then, assemble the
scored, chipped, or worn surface should be replaced.
Typical examples of unsatisfactory bearings and their
piston. piston pin and connecting rod following the
causes are shown in Figure 19. The copper-lead bearing
procedures for assembly. It is not necessary to ream or
base may be visible through the bearing overlay. This
hone the pin bore in the connecting rod. Replace
does not mean that the bearing is worn. It is not
damaged connecting rod nuts and bolts. Check the
necessary to replace the bearing if the bearing clearance
connecting rods for bend or twist on a suitable alignment
is within recommended limits.
fixture. Follow the instructions of the fixture manufacturer.
If the bend and/or twist exceeds specifications, the
Check the clearance of bearings that appear to be
connecting rod must be straightened or replaced.
satisfactory with Plastigage as detailed under Main and
PISTONS, PINS AND RINGS
Connecting Rod Bearings.
Remove deposits from the piston surfaces. Clean gum or
varnish from the piston skirt, piston pins and rings with
After any cylinder bore repair operation, such as
solvent. Do not use a caustic cleaning solution or a
honing or deglazing. clean the bore(s) with soap or
wire brush to clean pistons.
detergent and water. Then, thoroughly rinse the bore(s)
Clean the ring grooves with a ring groove cleaner
with clean water to remove the soap or detergent. and
Figure 18). Make sure the oil ring slots (or holes) are
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.
If the engine is disassembled, thoroughly clean the
block with solvent. Remove old gasket material from all
machined surfaces. Remove all pipe plugs that seal oil
passages; then clean out all the passages. Blow out all
passages, bolt holes, etc.. with compressed air. Make
sure the threads in the cylinder head bolt holes are clean.
FIG. 18 Cleaning Piston Ring Grooves
Dirt in the threads may cause binding and result in a false
torque reading. Use a tap to true up threads and to
remove any deposits. Thoroughly clean the grooves in the
crankshaft bearings and bearing retainers.