Kubota WG972-E2 Workshop Manual page 123

WG972-E2, DF972-E2, WSM
Correcting Valve and Valve Seat
■
NOTE
• Before correcting the valve and seat, check the valve stem
and the I.D. of valve guide section, and repair them if
necessary.
• After correcting the valve seat, be sure to check the valve
recessing.
1) Correcting Valve
1. Correct the valve with a valve refacer.
Valve face angle Factory spec.
2) Correcting Valve Seat
1. Slightly correct the seat surface with a 0.785 rad (45 °) valve seat
cutter.
2. Fitting the valve, check the contact position of the valve face and
seat surface with prussian blue. (Visual check) [If the valve has
been used for a long period, the seat tends to come in contact
with the upper side of the valve face.]
3. Grind the upper surface of the seat with a 0.262 rad (15 °) valve
seat cutter until the valve seat touches to the center of the valve
face (so that (a) equals (b) as shown in the figure.)
4. Grind the seat with a 0.785 rad (45 °) valve seat cutter again, and
visually recheck the contact between the valve and seat.
5. Repeat steps 3 and 4 until the correct contact is achieved.
6. Continue lapping until the seated rate becomes more than 70 %
of the total contact area.
Valve seat angle Factory spec.
(1) Valve Seat Cutter
(A) Check Contact
(B) Correct Seat Width
(C) Check Seat Surface
(D) Check Contact
Valve Lapping
1. Apply compound evenly to the valve lapping surface.
2. Insert the valve into the valve guide. Lap the valve onto its seat
with a valve flapper or screwdriver.
3. After lapping the valve, wash the compound away and apply oil,
then repeat valve lapping with oil.
4. Apply prussian blue to the contact surface to check the seated
rate. If it is less than 70 %, repeat valve lapping again.
■
IMPORTANT
• When valve lapping is performed, be sure to check the valve
recessing and adjust the valve clearance after assembling
the valve.
S-53
GASOLINE / LPG ENGINE
0.785 rad
45 °
0.785 rad
45 °
(a) Identical Dimensions
(b) Valve Seat Width
(c) 0.262 rad (15 °)
(d) 0.785 rad (45 °)
W1028220
W1061709
KiSC issued 01, 2006 A