Jeep Cherokee 1999 Electronic Service Manual page 1106

X J
DI SASSEM BLY AN D ASSEM BLY (Cont inue d)
Fig. 61 Valve Facing Margin
VALVE SEA T REFACING
(1) In st a ll a pilot of t h e cor r ect size in t h e va lve
gu ide bor e. Refa ce t h e va lve sea t t o t h e specified
a n gle wit h a good dr essin g st on e. Rem ove on ly
en ou gh m et a l t o pr ovide a sm oot h fin ish .
(2) Use t a per ed st on es t o obt a in t h e specified sea t
widt h wh en r equ ir ed.
(3) Con t r ol va lve sea t r u n ou t t o a m a xim u m of
0.0635 m m (0.0025 in .) (F ig. 62).
Fig. 62 Measurement of Valve Seat Runout
VALVE STEM OIL SEAL REPLACEMENT
Va lve st em oil sea ls a r e in st a lled on ea ch va lve
st em t o pr even t r ocker a r m lu br ica t in g oil fr om
en t er in g t h e com bu st ion ch a m ber t h r ou gh t h e va lve
gu ide bor es. On e sea l is m a r ked INT (in t a ke va lve)
a n d t h e ot h er is m a r ked E XH (exh a u st va lve).
Repla ce t h e oil sea ls wh en ever va lve ser vice is per-
for m ed or if t h e sea ls h a ve det er ior a t ed.
VALVE GUIDES
Th e va lve gu ides a r e a n in t egr a l pa r t of t h e en gin e
cylin der h ea d a n d a r e n ot r epla cea ble.
Wh en t h e va lve st em gu ide clea r a n ce is excessive,
t h e va lve gu ide bor es m u st be r ea m ed over size. Ser-
vice va lves wit h over size st em s a r e a va ila ble in 0.076
m m (0.003 in ch ) a n d 0.381 m m (0.015 in ch ) in cr e-
m en t s.
Cor r espon din g over size va lve st em sea ls a r e a lso
a va ila ble a n d m u st be u sed wit h va lves h a vin g 0.381
m m (0.015 in ch ) over size st em s.
NOTE: If the valve guides are reamed oversize, the
valve seats must be ground to ensure that the valve
seat is concentric to the valve guide.
VALVE STEM-TO-GUIDE CLEARANCE
MEASUREMENT
Va lve st em -t o-gu ide clea r a n ce m a y be m ea su r ed by
eit h er of t h e followin g t wo m et h ods.
PREFERRED METHOD
(1) Rem ove t h e va lve fr om t h e h ea d.
(2) Clea n t h e va lve st em gu ide bor e wit h solven t
a n d a br ist le br u sh .
(3) In ser t a t elescopin g ga u ge in t o t h e va lve st em
gu ide bor e a ppr oxim a t ely 9.525 m m (.375 in ch ) fr om
t h e va lve spr in g side of t h e h ea d (F ig. 63).
Fig. 63 Measurement of Valve Guide Bore Diameter
(4) Rem ove a n d m ea su r e t elescopin g ga u ge wit h a
m icr om et er.
(5) Repea t t h e m ea su r em en t wit h con t a ct s len gt h -
wise t o en gin e cylin der h ea d.
4.0L ENGINE 9 - 89