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tightness. If the we·ar, cqrrossion and out - of - roundness of the
valve
~nd
seat are not serious
~nd
their contact band width .is less
than 2· 5 mm; then the contact band can be lapped with lapping
compound, It is important to prevent the lapping compound from
g~tting
illto the valve guide when lapping the contact band. Well
lapped contact band of valve and valve seat should be even ,contin-
uous and in ·greyish white, colour without pitting ,scrape and
briliant line.
After
lapping, both the valve and valve s.eat must be
carefully cleaned 'with
kerosine or diesel fuel; the.n, put the related·
side~
'0£
cylinder head upvl.ard after. the lapped valve is mounted
with its springs, an'd fill some kerosine into the .port. After
2 - 3
minutes, if there is no leakage, the contact surfaces are;proven in
good air tightness.
(3)Reaming and Replacing Valve Seat
The valve seat can be reconditioned'if it is burnt out or out-
of-roundness s.eriously. First of all ,ream the valve seat by means
of a 15° and
7~oincii'Q,ed
angle reamer with a
guid.~
rod of 9 mm in
diameter.
Nex:t}rea~'ith.econtact
band of the valve seat with a
reamer of
45o?:f~~~ihed
angle
until the
conta~.t
band is rounded. The
contact band ~~t,ltlishou:tdlbe of'1.3-1. 5 mm ~.s-.shown in Fig. 7.
,'
.............
/
'.
I
,
I
/
Fig. 7 Diagram of reconditioIling v"alve seat
28
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