Jeep Cherokee 1999 Electronic Service Manual page 1115

9 - 2 ENGINE
GEN ERAL I N FORM AT I ON (Cont inue d)
Engine Description
HYDRAULIC TAPPETS
Befor e disa ssem blin g a n y pa r t of t h e en gin e t o cor-
r ect t a ppet n oise, ch eck t h e oil pr essu r e. If veh icle
h a s n o oil pr essu r e ga u ge, in st a ll a r elia ble ga u ge a t
t h e pr essu r e sen din g u n it . Th e pr essu r e sh ou ld be
bet ween 4 ba r s (50 psi) a t 3000 RP M.
Ch eck t h e oil level a ft er t h e en gin e r ea ch es n or m a l
oper a t in g t em per a t u r e. Allow 5 m in u t es t o st a bilize
oil level, ch eck dipst ick. Th e oil level in t h e pa n
sh ou ld n ever be a bove t h e F ULL m a r k or below t h e
ADD OIL m a r k on dipst ick. E it h er of t h ese 2 con di-
t ion s cou ld be r espon sible for n oisy t a ppet s:
OIL LEVEL HIGH
If oil level is a bove t h e F ULL m a r k, it is possible
for t h e con n ect in g r ods t o dip in t o t h e oil. Wit h t h e
en gin e r u n n in g, t h is con dit ion cou ld cr ea t e foa m in
t h e oil pa n . F oa m in oil pa n wou ld be fed t o t h e
h ydr a u lic t a ppet s by t h e oil pu m p ca u sin g t h em t o
lose len gt h a n d a llow va lves t o sea t n oisily.
OIL LEVEL LOW
Low oil level m a y a llow oil pu m p t o t a ke in a ir.
Wh en a ir is fed t o t h e t a ppet s, t h ey lose len gt h wh ich
a llows va lves t o sea t n oisily. An y lea ks on in t a ke side
of oil pu m p t h r ou gh wh ich a ir ca n be dr a wn will cr e-
a t e t h e sa m e t a ppet a ct ion . Ch eck t h e lu br ica t ion
syst em fr om t h e in t a ke st r a in er t o t h e pu m p cover,
in clu din g t h e r elief va lve r et a in er ca p. Wh en t a ppet
n oise is du e t o a er a t ion , it m a y be in t er m it t en t or
con st a n t , a n d u su a lly m or e t h a n 1 t a ppet will be
n oisy. Wh en oil level a n d lea ks h a ve been cor r ect ed,
oper a t e t h e en gin e a t fa st idle. Ru n en gin e for a su f-
ficien t t im e t o a llow a ll of t h e a ir in side t h e t a ppet s
t o be bled ou t .
DI AGN OSI S AN D T EST I N G
SERVICE DIAGNOSIS—DIESEL—
PERFORMANCE
SERVICE DIAGNOSIS—DIESEL—MECHANICAL
TAPPET NOISE
(1) To det er m in e sou r ce of t a ppet n oise, oper a t e
en gin e a t idle wit h cylin der h ea d cover s r em oved.
(2) F eel ea ch va lve spr in g or r ocker a r m t o det ect
n oisy t a ppet . Th e n oisy t a ppet will ca u se t h e a ffect ed
spr in g a n d/or r ocker a r m t o vibr a t e or feel r ou gh in
oper a t ion .
NOTE: Worn valve guides or cocked springs are
sometimes mistaken for noisy tappets. If such is
the case, noise may be dampened by applying side
thrust on the valve spring. If noise is not apprecia-
bly reduced, it can be assumed the noise is in the
tappet. Inspect the rocker arm push rod sockets
and push rod ends for wear.
(3) Va lve t a ppet n oise r a n ges fr om ligh t n oise t o a
h ea vy click. A ligh t n oise is u su a lly ca u sed by exces-
sive lea k down a r ou n d t h e u n it plu n ger or by t h e
plu n ger pa r t ia lly st ickin g in t h e t a ppet body cylin der.
Th e t a ppet sh ou ld be r epla ced. A h ea vy click is
ca u sed by a t a ppet ch eck va lve n ot sea t in g or by for-
eign pa r t icles becom in g wedged bet ween t h e plu n ger
a n d t h e t a ppet body. Th is will ca u se t h e plu n ger t o
st ick in t h e down posit ion . Th is h ea vy click will be
a ccom pa n ied by excessive clea r a n ce bet ween t h e
va lve st em a n d r ocker a r m a s va lve closes. In eit h er
ca se, t a ppet a ssem bly sh ou ld be r em oved for in spec-
t ion a n d clea n in g.
Th e va lve t r a in gen er a t es a n oise ver y m u ch like a
ligh t t a ppet n oise du r in g n or m a l oper a t ion . Ca r e
m u st be t a ken t o en su r e t h a t t a ppet s a r e m a kin g t h e
n oise. In gen er a l, if m or e t h a n on e t a ppet seem s t o
be n oisy, it s pr oba bly n ot t h e t a ppet s.
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