Jeep UNIVERSAL CJ-2A - Page 75

E
F4-134 ENGINE
the cylinder block. Replace valve guides which are
broken or worn enough to cause excessive valve
stem-to-guide clearance. See Par. E-63.
Standard intake valve clearance is .0007" to .0022"
[0,01778 a 0,05588 mm.] and the exhaust valve
clearance is .0025" to .0045" [0,0635 a 0,1143 mm.].
Excessive clearance between the valve stems and
guides will cause improper seating and burned
valves. When there is a tendency to draw oil vapor
through the guide causing excessive oil consump-
tion, fouled spark plugs, and poor low-speed per-
formance. To check the clearance of the valve stem
to the valve guide, take a new valve and place in
each valve guide. Check the clearance with a
suitably mounted dial indicator or feel the clearance
by moving the valve stem back and forth. If this
check shows excessive clearance it will be necessary
to replace the valve guide.
E-SO. Refacing Valves
Reface the valves with a valve refacer. The valve
refacer manufacturer's instructions should be fol-
lowed carefully to ensure a valve face concentric
with the valve stem. Reface both intake and ex-
haust valves to an angle of 45°. Take off only the
minimum of metal required to clean up the valve
faces.
If the thickness of the edge of the valve head is
reduced to less than Ys2" [0,8 mm.] replace the valve.
Note: Cocked or deformed valve springs or im-
properly installed or missing locks can be responsible
for valve problems.
FIG. 91-GAUGING VALVE SEATS
E-61. Valve Seat Inspection and Refacing
Inspect the valve seats for cracks, burns, pitting,
ridges, or improper angle. During any general
engine overhaul it is advisable to reface the valve
seats in both the cylinder block and head regardless
of their condition. If the valve gmdes are to be re-
placed, this must be done before refacing the valve
seats. Note that later engines have hardened
exhaust valve seat inserts.
Valve seat inserts must be concentric with finish
74
ream of valve stem guides (exhaust) within .002"
[0,051
mm.] total indicator reading.
When necessary to reface the valve seats, use a
valve seat grinder in accordance with the grinder
manufacturer's instructions. Any grinding of valve
seats should be preceded by touching up the
grinding stone so that their angles are accurate and
the stone is not clogged. Grind each valve seat to
a true 45° angle. Never grind any more than is
necessary to clean up pits, grooves, or to correct
the valve seat runout. Check the valve seats with
a dial indicator as shown in Fig. 91 after refacing.
FIG. 92·-REFACING VALVES
1-Valve Refacer
2-Valve
The valve seat should not be out of round more
than .002" [0,051 mm.]. A simple check can be
made in the absence of a dial indicator by spreading
a thin coat of pencil lead or bearing-fitting blue on
the valve face and then inserting the valve into
the valve seat. With hand pressure, rotate the valve
a quarter turn and then remove the valve and ob-
serve the transfer of blue (or pencil lead) to the
valve seat. An uneven transfer will indicate an
inaccurate valve and valve seat refacing operation.
After the seat is ground, check its width with a
seat width scale or a steel scale placed across the
face of the seat. The valve seat width after ref acing
should measure ~:)
2
" [2,3 mm.] and not wider than
Ys" [3,2 mm.]. Valve seat width is vital. Too wide
a seat can cause seat burning as it tends to trap
and hold carbon particles. Seats that are too narrow
will !'Ot transfer heat to the coolant rapidly enough
to keep the valves in proper operating condition.
When a valve seat has been refaced several times
or where it must be cut deeply for adequate recon-
ditioning, the seat may become too wide for efficient
operation. Narrow the seat without changing its
position in relation to the valve face by using a
valve seat relief counterbore above the seat and a
valve seat narrowing cutter below the seat. These
operations are performed only after the valve seats
have been refaced and then only when necessary.
The finished valve seat should contact the approxi-
mate center of the valve face. Check by applying
an extremely thin coat of p@ncil lead or bearing-
fitting blue to the seat. Then install and rotate the
valve with light pressure. Blue (or pencil marks)