0141
Basic Enaine
0141
OVERHAUL (Continued)
Fitting Piston Pins
The piston pins are selected to give the correct fit in the
piston pin bore and bushing in the connecting rod. Pistons
are only supplied in service complete with the piston pin, to
ensure the correct fit. The piston pins should not be
interchanged.
Valve Rocker Arm and/or Shaft Assembly
Dress up minor surface defects on the rocker arm shaft
and in the rocker arm bore with a hone.
If the pad at the valve end of the rocker arm has a grooved
radius, replace the rocker arm.
Do not attempt to true this
surface by grinding.
Push Rods
Following the procedures under Push Rod Inspection,
check the push rods for straightness.
If the runout exceeds the maximum limit at any point,
discard the rod.
Do not attempt to straighten push rods.
Cylinder Block
Refinishing Cylinder Walls
Honing is recommended for refinishing cylinder walls
only
when the walls have minor scuffs or scratches, or for fitting
pistons to the specified clearance. The grade of hone to be
used is determined by the amount of metal to be removed.
Follow the instructions of the hone manufacturer. If coarse
stones are used to start the honing operation, leave
enough material so that all hone marks can be removed
with the finishing hone which is used to obtain the proper
piston clearance. Cylinder walls that are severely marred
and/or worn beyond the specified limits should be
refinished.
Before any cylinder is refinished, all main
bearing caps must be in place and tightened to the
proper torque so that the crankshaft bearing bores will
not become distorted from there finishing operation.
Refinish only the cylinder or cylinders that require it. All
pistons are the same weight, both standard and oversize;
therefore, various sizes of pistons can be used without
upsetting engine balance. Refinish the cylinder with the
most wear first to determine the maximum oversize. If the
cylinder will not clean up when refinished for the maximum
oversize piston recommended, replace the block. Refinish
the cylinder to within approximately 0.04 mm (0.0015 inch)
of the required oversize diameter. This will allow enough
stock for the final step of honing so that the correct surface
finish and pattern are obtained. For the proper use of the
refinishing equipment follow the instructions of the
manufacturer. Only experienced personnel should be
allowed to perform this work. Use a motor-driven, spring
pressure-type hone at a speed of 300500 rpm. Hones of
grit sizes 180-220 will normally provide the desired bore
surface finish of 1532 RMS. When honing the cylinder
bores use a lubricant mixture of equal parts of kerosene
and SAE No. 20 motor oil. Operate the hone in such a way
to produce a cross-hatch finish on the cylinder bore. The
cross-hatch pattern should be at an angle of approximately
30 degrees to the cylinder bore. After the final operation in
either of the two refinishing methods described and prior to
checking the piston fit, thoroughly clean and oil the cylinder
walls. Mark the pistons to correspond to the cylinders in
which they are to be installed. When the refinishing of all
cylinders that require it has been completed and all pistons
are fitted, thoroughly clean the entire block and oil the
cylinder walls.
Repairing Sand Holes or Porous Engine Castings
Porosity or sand hole(s) which will cause oil seepage or
leakage can occur with modern casting processes. A
complete inspection of engine and transmission should be
made. If the leak is attributed to the porous condition of the
cylinder block or sand hole(s), repairs can be made with
metallic plastic (part No. CGAZ-19554-A).
Do not repair
cracks with this material.
Repairs with this metallic plastic
must be confined to those cast iron engine component
surfaces where the inner wall surface is not exposed to
engine coolant pressure or oil pressure. For example:
1. Cylinder block surfaces extending along the length of
the block, upward from the oil pan rail to the cylinder
water jacket but not including machined areas.
2.
Lower rear face of the cylinder block.
3.
Intake manifold casting.
4.
Cylinder head, along the rocker arm cover gasket
surface.
The following procedure should be used to repair porous
areas or sand holes in cast iron.
1.
2.
3.
4.
5.
6.
Clean the surface to be repaired by grinding or rotary
filing to a clean bright metal surface. Chamfer or
undercut the hole or porosity to a greater depth than
the rest of the cleaned surface. Solid metal must
surround the hole. Openings larger than 6.4 mm
(l/4 inch) should not be repaired using metallic
plastic. Openings in excess of 6.4 mm (l/4 inch) can
be drilled, tapped and plugged using common tools.
Clean the repair area thoroughly. Metallic plastic will
not stick to a dirty or oily surface.
Mix the metallic plastic base and hardener as directed
on the container. Stir thoroughly until uniform.
Apply the repair mixture with a suitable clean tool,
(putty knife, wood spoon, etc.) forcing the epoxy into
the hole or porosity.
Allow the repair mixture to harden. This can be
accomplished by two methods, heat cure with a
121 degrees C (250 degrees F) lamp placed 254 mm
(10 inches) from the repaired surface, or air dry for
1 O-l 2 hours at temperatures above IO degrees
C
(50 degrees F).
Sand or grind the repaired area to blend with the
general contour of the surrounding surface.
Paint the surface to match the rest of the block.
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