Dnepr MT9 - Cylinder Head; Piston Pin Repair; Valve Timing Gear Repair

Pistons mu st be se lected such as to mat ch the cy lind er not only
by the diameter of th e ski rt , but also by th eir weight. The difierence
in the weig ht of the e ng ine pistons mu st n ot exceed 4 g.
With this kind of pi stons, th e colour marking of the piston pin
openings must corres pond to the marking of the opening of the con-
necting rod small end.
Piston Pin
Examine 1.he extern a I s urfa ce of the pin, checl< it for the absence
of notches, dents, bronze ga lling a nd noticeable wear.
The wear of th e pi sto n pin to be measured al ong the edges and
in the middl e part of it, mu st not exceed 0.015 mm of the minimal
size of th e colour marking .
When re pl aci ng the connecting rod, the bush in th e connecting
rod sma ll end, the pis ton or pin itself, select a new pin of th e co-
lo ur marking corresponding to that of th e piston pin open ings and
of the connecting rod sma ll end.
The
se lection of pins for co nn ect ing rods sho uld be carried out at
room temperature of 20± 5°C.
Repairing the Valve Timing Gear
The va lve timing gear has to be re pair ed in cases the follo wing
fa ult s a re det ected in the e ngine:
com pr ess ion drop in th e cylinders due to poor air-tightness of
lhe
yalves, accompanied by power drop, increased pe trol consump-
tion and impeded starting of the e ngin e;
incr
eased noi se during operation of th e va lve gear;
in th e case of total disassembly of the engine, if some of th e
compone nt part s of the valve timing gear are found to be defective.
Cylinder Head
Examine al l th e accessible p ~ ace s in the cylinder head for the
absence of cracks a nd other s igns of damage, make sure t hat the
\·alves are not burnt out and the thr ea ds of screw not stripped. Re-
move the valves to in spect them and other parts- s pring s, va l ve
guides and valve sea ts - for good condition, and to m ake the neces-
sary m eas ur eme nts for dete rmining the amou nt of wear (Fig. 15) .
• In order to remov e th e valves, proceed as follows:
m
ark the valves;
fix the cyl inder head on an appliance OCE-4659;
compr ess th e valve springs a nd tak e out the slide blo cks ;
remove th e upper s pring disks, springs, lower disks wit h wash-
ers and tak e out the valves.
Thoroughly clean th e t aken -out parts to remove car bon and re-
sinous d eposits, th en wash these parts. Afler washi ng, check them for
good co ndition.
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