Dnepr MT10-36 - Lapping the Valves; Spark Timing

water jacket and the pro visio n of numerous fins on th e cylinders ~
c rankcase and cylinder heads. Therefore, some r ecurrent knocks of
t he valves a nd tappets, at normal clearances between the va lve ·
ste m (cap) and the rocker en d, as well as an even high-pitched (not
shrill) noise prod uced during operation of the valve timing gear
drive sho u ld not be regarded as an indication of malfunction.
In t he case of partial disassembly involving the removal of the
cy lind er heads, the thread of the nuts fasten ' ing the exhaust pipes,
a nd of the cy lind er head filters should be lubricated during asse m-
bly with graphite gre ase type BBH-1 GOST 5656-60.
Aft - er 10000 km run do not fail to check the condition of valves.
and lap them int o their seats, if req uired.
Lap pi ng the Valves
To lap the valve into the seat of the cylin der head, slip a spring:
over the stem of the val ve to be lapped , apply a thin layer -of abra-
sive paste to the cha mfer of valve he ad and, after inserting the val -
ve with the pressing-out spring i nto the guide bush, fit an appliance
for .rotating t he valve (a bit brace or a drill) on the end of the va lve
stem.
Use may be also made of a piece of a petr ol ho se by t urning it
be tween the pa lms of your h ands. Using th e above appliance, rotate
t he valve in either directio n in such a manner that the turn in one
direction is about twice as long as th e turn in the oppos i te dire ct ion,
i. e. ensure th at the va l ve is gradually turned in one directi on. When
c hanging th e dir ect ion of turn"ing, the valve must be lifted off its.
seat.
Lap the valve into the head seat carefully .so as n ot to remov e
too mu ch met al from the working chamfers as th is will redu ce the
nu mber o.f permissible repa i rs. Towards the end of lapping, reduce
the amount of pas te and, at the last stage, perform lapping with the
use of clea n oil.
A lustreless unifo rm c olour appearing on the wor king surf aces.
of the valve head an d seat is an indi cation of a satisfactory lap-
ping . Afte r lapping, thoroughly wash the valves, the valve seat s,
guide bu shes, fi ller and com p ression chamber of t he cylinder head
until the abrasive paste is com p·le tely remo ve d.
Follo wi ng that, c heck whether the valves are fitted ti ghtl y, fo r
which purpose inst all the valv es in place, and pour k erose ne fi rst
i nt o the inlet, then in to the exhau . st port of the cyli nd er head. The
kero se ne mu st not leak out within 30 s after filling. If the ker ose ne
starts to l eak before t he speci . fi ed peri od elapses this m eans that an
ad ditional la p ping is required.
Spark Ti ming
To faciilitate the sett ing of the igni tion advance a ngl e, the e ngi-
ne flywheel i<> pr ovide d on the ou t side with marks a nd lett er s "B"
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