Dnepr MT9 - Piston Repair; Piston Rings Repair

cylinder, m eas ureme nt s to be made in two plan es: in th e plan e
of
connecting rod swinging and in the pl ane perpendicular to the
former on e.
If the wear exceeds the va lues specified in Tab le 4, the cylinder
has to be bored o. u.t to suit the nearest r epa ir size of the piston.
After fini shing, was h th e cy lind er face with a brus h moistened
with aqu eous solution of soa p, then wip e it dry with a pie ce of cl ea n
dry cloth.
Piston Rings
A tardy re pla ceme nt of the piston ring s will l ead to prematur e
wear of the cylinder wa ll s a nd of the ring s themselves, to r a pid ac-
cum ui<Jtion of carbon deposits and incr ease d oil consumption.
Before checking the pi sto n rings for condi ,tion, clean them of car-
bon and wash.
If , dur ing in sp ect ion, th e pi s ton rings are found to be defecti ve
(cracks, chips, larg e areas that has not been l apped to the cylinder,
dimini shed fl exibility of the ring s themselves), replace the rings.
The ring must be also replaced if its average width is found to
be 0.05 mm l ess th an the l east size spec ified in Table 3 or th e radial
thic kn ess is l ess than 2.7 mm, or if the piston ring gap in bore is
gr
ea t er lhan 1.5 mm.
When re pairing the cy lind er, re plac e th e pis ton rings with repair
ones of the ap pr opri ate size.
Rc rJai r g-roups
PI
P2
Repair sizes
of cyli nde rs
P is ton Nos
78.20- 78.23 MT 801237-Pl
78.50- 78.53 MT801237-P2
Piston
Piston sizes
78 .14 - 78. 17
78.44- 78.4 7
Tabla 6
R emarks
Before atte mptin g inspection and m eas ur eme nt s, clean th e pi ston
to re mo ve carbon depos it s, especiall y from the piston h ea d a nd
grooves, then was h th e pi sto n.
Make s ur e that the pi ston sk irt is free of sco res and cracks and
that th e lo cking ring gr ooves in the piston pin opening are intact
an d not worn out.
The pe rmi ss ible wear of th e pi s ton pin opening mu st not be grea-
te r than 0.02 mm . If the piston pin opening a nd pi s ton ring grooves
beco me worn beyond permi ss ible limit s, or if scores a re found on
the piston skirt, the piston mu st be replaced.
When replacing the pis tons for the first time in the cylinders
that are n eg ligibly worn and do n ot re quir e boring a nd polishing,
install the sta ndard size pistons of the group co rr esp on ding to the
t actual size of the cy linder.
'I
I
It
[,8
'\