Jeep Cherokee 1999 Electronic Service Manual page 1076

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DESCRI PT I ON AN D OPERAT I ON (Cont inue d)
OIL PUMP PRESSURE
Th e MINIMUM oil pu m p pr essu r e is 89.6 kP a (13
psi) a t 600 r pm . Th e NORMAL oil pu m p pr essu r e is
517 kP a (75 psi) a t 1600 r pm or m or e.
SERV I CE PROCEDU RES
VALVE TIMING
Discon n ect t h e spa r k plu g wir es a n d r em ove t h e
spa r k plu gs.
Rem ove t h e en gin e cylin der h ea d cover.
Rem ove t h e ca pscr ews, br idge a n d pivot a ssem bly,
a n d r ocker a r m s fr om a bove t h e No.1 cylin der.
Alt er n a t ely loosen ea ch ca pscr ew, on e t u r n a t a
t im e, t o a void da m a gin g t h e br idge.
Rot a t e t h e cr a n ksh a ft u n t il t h e No.6 pist on is a t
t op dea d cen t er (TDC) on t h e com pr ession st r oke.
Rot a t e t h e cr a n ksh a ft cou n t er clockwise (viewed
fr om t h e fr on t of t h e en gin e) 90°.
In st a ll a dia l in dica t or on t h e en d of t h e No.1 cyl-
in der in t a ke va lve pu sh r od. Use r u bber t u bin g t o
secu r e t h e in dica t or st em on t h e pu sh r od.
Set t h e dia l in dica t or poin t er a t zer o.
Rot a t e t h e cr a n ksh a ft clockwise (viewed fr om t h e
fr on t of t h e en gin e) u n t il t h e dia l in dica t or poin t er
in dica t es 0.305 m m (0.012 in ch ) t r a vel dist a n ce (lift ).
Th e t im in g n ot ch in dex on t h e vibr a t ion da m per
sh ou ld be a lign ed wit h t h e TDC m a r k on t h e t im in g
degr ee sca le.
If t h e t im in g n ot ch is m or e t h a n 13 m m (1/2 in ch )
a wa y fr om t h e TDC m a r k in eit h er dir ect ion , t h e
va lve t im in g is in cor r ect .
If t h e va lve t im in g is in cor r ect , t h e ca u se m a y be a
br oken ca m sh a ft pin . It is n ot n ecessa r y t o r epla ce
t h e ca m sh a ft beca u se of pin fa ilu r e. A spr in g pin is
a va ila ble for ser vice r epla cem en t .
PISTON FITTING
BORE GAGE METHOD
(1) To cor r ect ly select t h e pr oper size pist on , a cyl-
in der bor e ga u ge, ca pa ble of r ea din g in 0.003 m m
(.0001 in .) INCRE ME NTS is r equ ir ed. If a bor e
ga u ge is n ot a va ila ble, do n ot u se a n in side m icr om e-
t er.
(2) Mea su r e t h e in side dia m et er of t h e cylin der
bor e a t a poin t 49.5 m m (1-15/16 in ch es) below t op of
bor e. St a r t per pen dicu la r (a cr oss or a t 90 degr ees) t o
t h e a xis of t h e cr a n ksh a ft a t poin t A a n d t h en t a ke
a n a ddit ion a l bor e r ea din g 90 degr ees t o t h a t a t poin t
B (F ig. 4).
(3) Th e coa t ed pist on s will be ser viced wit h t h e
pist on pin a n d con n ect in g r od pr e-a ssem bled. Th e
c o a te d p is to n c o n n e c tin g ro d a s s e m bly c a n be
u s e d to s e rv ic e p re v io u s bu ilt e n g in e s a n d
MU S T be re p la c e d a s c o m p le te s e ts . Tin coa t ed
pist on s sh ou ld n ot be u sed a s r epla cem en t s for coa t ed
pist on s.
(4) Th e coa t in g m a t er ia l is a pplied t o t h e pist on
a ft er t h e fin a l pist on m a ch in in g pr ocess. Mea su r in g
t h e ou t side dia m et er of a coa t ed pist on will n ot pr o-
vide a ccu r a t e r esu lt s (F ig. 3). Th er efor e m ea su r in g
t h e in side dia m et er of t h e cylin der bor e wit h a dia l
Bor e Ga u ge is MAN D ATORY. To cor r ect ly select t h e
pr oper size pist on , a cylin der bor e ga u ge ca pa ble of
r ea din g in 0.003 m m (.0001 in .) in cr em en t s is
r equ ir ed.
(5) P ist on in st a lla t ion
r equ ir es sligh t ly m or e pr essu r e t h a n t h a t r equ ir ed
for n on -coa t ed pist on s. Th e bon ded coa t in g on t h e
pist on will give t h e a ppea r a n ce of a lin e-t o-lin e fit
wit h t h e cylin der bor e.
Fig. 3 Moly Coated Piston
P IS TON S IZE CHART
CYLIN D ER B ORE S IZE P IS TON LETTER S IZE
98.438 t o 98.448 m m (3.8755 t o 3.8759 in .) . . . . . . A
98.448 t o 98.458 m m (3.8759 t o 3.8763 in .) . . . . . . B
98.458 t o 98.468 m m (3.8763 t o 3.8767 in .) . . . . . . C
98.468 t o 98.478 m m (3.8767 t o 3.8771 in .) . . . . . . D
98.478 t o 98.488 m m (3.8771 t o 3.8775 in .) . . . . . . E
98.488 t o 98.498 m m (3.8775 t o 3.8779 in .) . . . . . . F
PISTON RING FITTING
(1) Ca r efu lly clea n
gr ooves. Oil dr a in open in gs in t h e oil r in g gr oove a n d
pin boss m u st be clea r. DO NOT r em ove m et a l fr om
t h e gr ooves or la n ds. Th is will ch a n ge r in g-t o-gr oove
clea r a n ces a n d will da m a ge t h e r in g-t o-la n d sea t in g.
(2) Be su r e t h e pist on r in g gr ooves a r e fr ee of
n icks a n d bu r r s.
4.0L ENGINE
in t o t h e cylin der
t h e ca r bon fr om a ll r in g
9 - 59
bor e