ENGINE REPAIR (Cont'd)
Installing Piston Rings
The piston uses two compression rings and one oil control
ring. the lower compression ring
is
stepped on the bottom
outer edge and the upper ring
is
chrome plated and
tapered on the outside diameter. Both rings are marked
top and must be
installed correctly. The upper ring, when
new,
has a red and brown compound on the outer edge.
This compound must not
be
removed. The oil control
rings have narrow ring cases and can be installed either
way.
Use the correct size ring for the size of
cylinder bore you
have.
Put the ring
in
the cylinder bore it is going to be used
in.
Use the head of a piston to push the ring in the bore about
1 inch (25,4 mm) so that the ring
is
square with the
cylinder wall. Be careful not to damage the ring or the
cylinder bore.
Measure the gap between the ends of the ring with a
feel
gauge [A). If the ring gap
is
not in the specified limits, use
another ring set.
Check the side
clearance of the compression rings with
a
feeler gauge installed between the ring and its lower
edge [B]. The gauge must move easily around the ring
circumference.
If the grooves are worn, make
replacement of the piston.
Installing The Piston Pins
Pistons and piston pins are available as a unit only and
cannot
be
purchased as individual parts. Keep the correct
pins and pistons together.
Valve Rocker Arm And Shaft Assembly
Use a hone to remove small surface damage to the rocker
arm shaft and to the rocker arm bore.
If
the valve end of the rocker arm has a grooved radius
replace the rocker arm.
You
cannot grind this surface.
Push Rods
Make sure the push rods are straight.
If the push rod is not
in
specification replace the push rod.
CYLINDER BLOCK
Finishing The Cylinder Walls
Before any cylinder is machined all main bearing caps
must be
pOSitioned
and tightened to the correct torque.
Finish
only the cylinder or cylinders that need to be
finished.
All pistons are the same weight, both standard
and oversize; and various sizes of pistons can be used
without changing the engine
balance. Finish the cylinder
with the most wear first to find the maximum oversize.
Revised Oct. 97
-7B-17-
741, 742, 743,
7430S
Bobcat Loader
Service Manual
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