Chrysler RAM TRUCK 2500 1994 Service Manual page 754

(2) Hold the oil pump base flush against mating
surface on No.4 main bearing cap. Finger tighten
pump attaching bolts. Tighten attaching bolts to 41
N-m (30 ft. lbs.) torque.
(3) Install the oil pan.
PISTON / CONNECTING ROD ASSEMBLY
The pistons are elliptically turned so that the di­
ameter at the pin boss is less than its diameter
across the thrust face. This allows for expansion un­
der normal operating conditions. Under operating
temperatures, expansion forces the pin bosses away
from each other, causing the piston to assume a more
nearly round shape.
A l l pistons are machined to the same weight, re­
gardless of size, to maintain piston balance.
The piston pin rotates i n the piston only and is re­
tained by the press interference fit of the piston pin
in the connecting rod.
R E M O V A L
(1) Remove the engine from the vehicle.
(2) Remove the cylinder head.
(3) Remove the oil pan.
(4) Remove top ridge of cylinder bores w i t h a reli­
able ridge reamer before removing pistons from cyl­
inder block. Be sure to keep tops of pistons covered
during this operation.
(5) Be sure the connecting rod and connecting rod
cap are identified with the cylinder number. Remove
connecting rod cap. Install connecting rod bolt guide
set on connecting rod bolts.
(6) Pistons and connecting rods must be removed
from top of cylinder block. When removing piston and
connecting rod assemblies, rotate crankshaft center
the connecting rod i n the cylinder bore and at BDC.
Be careful n o t t o n i c k crankshaft j o u r n a l s .
(7) After removal, install bearing cap on the mat­
ing rod.
INSPECTION
Check the crankshaft connecting rod journal for ex­
cessive wear, taper and scoring.
Check the cylinder block bore for out-of-round,
taper, scoring and scuffing.
Check the pistons for taper and elliptical shape be­
fore they are fitted into the cylinder bore (Fig. 3).
FITTING PISTONS
Piston and cylinder wall must be clean and dry.
Specified clearance between the piston and the cylin­
der wall is 0.013-0.038 mm (0.0005-0.0015 inch).
Piston diameter should be measured at the top of
skirt, 90° to piston pin axis. Cylinder bores should be
measured halfway down the cylinder bore and trans­
verse to the engine crankshaft center line.
Pistons and cylinder bores should be measured at
normal room temperature, 21°C (70°F).
DIAMETER (D)
SHOULD BE
0.0000-0.0152 mm
(0.0000-0.0006 in.
LARGER THAN (C).
98.704-98.831 mm
- ( 3 . 8 8 6 - 3 . 8 9 1 i n . ) -
•98.577-98.704 mm -
(3.881-3.886 in.)
62.230 mm
(2.45 in,
i
ELLIPTICAL SHAPE OF THE PISTON
SKIRT SHOULD BE 0.254-0.304 mm
(0.010-0.012 in.) LESS AT DIAMETER
(A) THAN ACROSS THE THRUST
FACES AT DIAMETER (B).
J9309-9
Fig. 3 Piston Measurements
FITTING RINGS
(1) Measurement of end gaps:
(a) Measure piston ring gap 2 inches from bot­
tom of cylinder bore. A n inverted piston can be
used to push the rings down to ensure positioning
rings squarely i n the cylinder bore before measur­
ing.
(b) Insert feeler gauge i n the gap. The top com­
pression ring gap should be between 0.254-0.508
mm (0.010-0.020 inch). The second compression
ring gap should be between 0.508-0.762 mm (0.020-
0.030 inch). The oil ring gap should be 0.254-1.270
mm (0.010-0.050 inch).
(c) Rings with insufficient end gap may be prop­
erly filled to the correct dimension. Rings with ex­
cess gaps should not be used.
(2) Install rings and confirm ring side clearance:
(a) Install oil rings being careful not to nick or
scratch the piston.
(b) Install the compression rings using Installa­
tion Tool C-4184. The top compression may be in­
stalled with either side up. The second compression
ring must be installed with the identification mark
face up (toward top of piston) and the chamfer
should face down. A n identification mark on the
ring is a drill point, a stamped letter "O", an oval
depression or the word TOP.
(c) Measure side clearance between piston ring
and ring land (Fig. 4). Clearance should be 0.038-
0.076 mm (0.0015-0.0030 inch) for the compression
rings. The steel rail oil ring should be free in
groove, but should not exceed 0.203 mm (0.0080
inch) side clearance.