Dnepr MT9 - Page 61

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When insp ecting the va lves, check the following:
stem-to -guid e side clear ance;
wea r of the ste m;
condition of the fitting chamfer of va lve h ead.
Check the s prin g for flexibility and fo r pr oper length in a free
sta te.
The
stem-to-guide side clearance must not be greater tha n
0.25 mm. If the clearance exceeds the specified fi g ur e, repl ace the
Yalve or guide bushing, or th e both compo ne nt s, for which purpose
measure the diameter of the valve stem and guide bus hin g at a dist-
ance of 5 mm from the upper a nd l ower edges of the working sur-
faces.
If the wea r of the valve stem is greater lhan 0.12 mm, re pla ce
the valve. If the bushing wea r exceeds 0.15 mm , repl ace the bushing.
The gu ide bus hing is to be replaced in t he following order:
thoroughly cl ean off carbo n from the guide bushing in the
throat;
fix the cyl inder head a nd pres s out lhe v alve guide bushing;
check the guide bushing opening fo r prop er cond ition, h eat the
cylinder h ea d up to 200°( and pr ess lhe b us hing back in place;
ream the guide bushing openin g by means of a reamer of 8 +o. o22
lo 8. 00-8 .03 mm in di ameter, check th e opening for being recti-
linear. After repair ing the guide bushing, check the va lve sea t c ham-
fer for con centric ity a nd , if n ecess ar y, work th e va l ve sea t c hamf er
with a milling c utt er.
In
case any pil s, worn -o ut or burnt places and other signs of da -
m
age are found on i.he working surf aces of the seats and va l ves,
these defects mu.sl be el imin ated by worki ng th e seat ch amfe r with
a mi lling cutter 3 -314 and by g rinding the va l ve h ead ch amfe r.
If the va lve h ead is excess ively wa rp ed or cracks arc found on
il, repl ace the va lve.
A
ft er g rinding, check the play of th e valve h ead chamfer with
respect to the stem, us ing an appliance nK-474 for this p urpo se. Th e
play
must not be grea t er than 0.03 mm.
After re pairing the sea t ch amfe r, check its conce ntr ici ty wi th
resp ect to the guide bu shing opening (Fig. 16) . The pe rmi ss ible play
must not exceed 0.03 mm.
If the va l ve seal is g reatly wo rn out or h as other d efects th at
ca
nnol be e limin ated by means of a millin g cutter, suc h a sea t must
be repl aced by a n ew one, for which pu rpo se proce ed as follows:
cut a
thr ea d on th e insid e of th e va l ve seat, h ea t the head to
a ppro x imatel y 200°C and remove the valve seat wit h the aid of a
lifter nP-1262 (Fig. 17) ;
heat the cylind er head agai n and pr ess in a new va l ve scat.
Af ter gr ind ing the va l ve h ead and wor king the sea t with the
milli ng cutter, it is n ecessary to lap their work ing cha mfers.
Lap
the va l ve head and seat in the following ord er:
fila s pring on lhe stem of the valve to be lapped;
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