Chrysler RAM TRUCK 2500 1994 Service Manual page 835

§ - 114 8.0L ENGINE
test between 100 and 109 N (22.5 and 24.5 pounds)
when compressed to 34 mm (1-11/32 inches). Replace
spring that fails to meet these specifications.
I f oil pressure was low and pump is within specifi­
cations, inspect for worn engine bearings or other
reasons for oil pressure loss.
INSTALLATION
(1) Lubricate the pump rotors i n engine oil and in­
stall i n the timing chain cover. Use new parts as re­
quired.
(2) Position the oil pump cover onto the timing
chain cover. Tighten cover bolts to 14 N-m (125 in.
lbs.) torque.
(3) Install the relief valve and spring.
(4) Using a new pressure relief valve gasket, in­
stall the relief valve plug. Tighten the plug to 20 N-m
(15 ft. lbs.) torque.
(5) Install the timing chain cover.
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.
The pistons have a unique dry-film lubricant coat­
ing baked onto the skirts to reduce friction. The lu­
bricant is particularly effective during engine break-
in, but with time, the material becomes embedded
into cylinder bore walls and continues to reduce fric­
tion.
REMOVAL
(1) Remove the engine from the vehicle.
(2) Remove the cylinder head.
(3) Remove the oil pan and oil pump pick-up tube.
(4) Remove top ridge of cylinder bores with 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 not to nick, crankshaft journals. D O
NOT try to remove black coating on skirt. This
is the dry film lubricant.
(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. 12).
DIAMETER (D)
SHOULD BE
0.0000-0.0152 mm
(0.0000-0.0006 in.
LARGER THAN (C)
98.704-98.831 mm
(3.886-3.891 in.)
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. 12 Piston Measurements
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).
FITTING RINGS
(1) Measurement of end gaps:
(a) Measure piston ring gap 2 inches from bot­
tom of cylinder bore. An 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 stock i n the gap. Gap for com­
pression rings should be between 0.254-0.508 mm
(0.010-0.020 inch).