Kubota B1830 Workshop Manual page 155

B1830,B2230,B2530,B3030, WSM
Correcting Valve and Valve Seat
NOTE
• Before correcting the valve and the 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.
Factory
Valve face angle specifica-
tion
2) Correcting Valve Seat
1. Slightly correct the seat surface with a 0.785 rad (45 °) / 1.047
rad (60 °) 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 0.523 rad (30 °) 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 0.262 rad (15 °) valve seat cutter again,
and visually recheck the contact between the valve and the
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.
Factory
Valve face angle specifica-
tion
(1) Valve Seat Width
(A) Check Contact
(B) Correct Seat Width
(C) Correct 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.
1-S54
ENGINE
1.047 rad
IN.
60 °
0.785 rad
EX.
45 °
1.047 rad
IN.
60 °
0.785 rad
EX.
45 °
(a) Identical Dimensions
(b) Valve Seat Width
(c) 0.262 rad (15 °)
(d) 0.785 rad (45 °)
9Y1210003ENS0082US0
9Y1210003ENS0083US0
KiSC issued 05, 2012 A