Briggs & Stratton 250000 Spécifications Page 180

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6
NOTE: SPECIFICATION TABLES BEGIN ON PAGE 11 OF THIS SECTION.
10
Counterbore Cylinder for Intake Valve Seat
Installation
Cast Iron Cylinder Models
Cast iron cylinder models must be counterbored to
allow installation of the intake valve seat insert.
1. Select proper seat insert, cutter shank, counter-
bore cutter, pilot and driver according to Table 6.
2. Insert pilot (1) in intake valve guide, Fig. 17.
NOTE:The Model Series 320000 intake valve
seat is part of the cylinder. There is no
replacement valve seat.
3. Assemble correct counterbore cutter (1) to cutter
shank (2) as shown in Figs. 18, 19.
4. Counterbore cylinder by hand until stop (3) on
cutter (1) touches top of cylinder, Fig. 19.
NOTE:Do not force the cutter to one side or it will
cut oversize.
5. Blow out all chips.
6. Use Knockout Pin, Tool #19135, to remove cutter
from cutter shank.
Fig. 17
1
Fig. 18
1
2
Valve Conversions
The life of a valve is considered to be the period of time
the valve will operate before repair or replacement is
necessary. The life of a standard exhaust valve is often
shortened because of burning, which occurs when
pieces of combustion deposit lodge between the valve
seat and valve face, preventing the valve from closing
completely. This is most likely to occur on engines
which are operated at constant speed and constant
load, for long periods of time. Exhaust valve life can be
extended by using:
a. A valve rotator turns the exhaust valve a slight
bit on each lift, wiping away any deposits
which tend to lodge between the valve face
and seat, Table No. 8, page 14 and Fig. 20 or,
b. For LP or Natural gas, use a Cobalite valve
without rotator, see Table No’s. 11 or 12,
pages 17 or 18, using Fig. 21 or Fig. 22 to
determine type of retainer being used.
c. A Cobalite exhaust valve which has a
greater resistance to heat, Table No. 9, page
15 or,
d. Or a combination of both the rotator and
Cobalite valve, Table No. 10, page 16.
Fig. 19
1
2
3
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