KTM 250 1998, Repair Manual

Page: 35 / 59

5.10 Piston and cylinder
– Before assembly, oil all parts thoroughly at the sliding points.
– Insert needle bearing in conrod eye, mount piston (arrow on piston head shows
direction for exhaust duct).
– Mount piston pin and wire circlips with open side showing downwards (see
sketch).
– Mount cylinder base gaskets.
– Place piston on selfmade wooden stand and position piston ring.
– Place on preassembled cylinder, remove wooden stand and tighten cylinder
down crosswise, using two nuts.
5.11 Adjusting Dimension „X“
D
IMENSION
„X“
IS THE DIMENSION FROM UPPER EDGE OF PISTON TO UPPER EDGE OF CYLIN
-
DER WITH CYLINDER UNDER LOW TENSION AND PISTON IN
TDC
POSITION
.
T
HE DIMENSION
„X“
SHOULD BE ADJUSTED EXTREMELY CAREFULLY BY INSERTING CYLINDER
BASE GASKETS OF SUITABLE THICKNESSES
.
!
CAUTION
!
I
F THE DIMENSION
„X“
IS TOO LARGE
,
THE COMPRESSION RATIO WILL BE REDUCED AND THE
ENGINE LOOSES POWER
. O
N THE OTHER HAND
,
IF THE DIMENSION
„X“
IS TOO SMALL
,
THE
ENGINE WILL PING AND OVERHEAT
.
– Place slide caliper on cylinder and use feeler gauge to measure distance between
piston and slide caliper.
D
IMENSION
”X” = 0
MM
+ 0.1
MM
(0.004
IN
).
– Tighten the collar nuts at the cylinder base with 35 Nm (26 ft.lb).
5.12 Adjusting control flap (dimension “Z“)
N
OTE
: D
IMENSION
“Z“
IS THE DISTANCE FROM THE LOWER EDGE OF THE CONTROL FLAP TO
THE UPPER EDGE OF THE CYLINDER
,
AS MEASURED IN THE CENTRE OF THE EXHAUST PORT
.
250 : Z = 48.0
MM
+ 0.2 / - 0.6
MM
300 : Z = 46.0
MM
+ 0.2 / - 0.6
MM
380 : Z = 50.5
MM
+ 0.2 / - 0.6
MM
250 : Z = 1.889
IN
+ 0.008
IN
/ - 0.024
IN
300 : Z = 1.811
IN
+ 0.008
IN
/ - 0.024
IN
380 : Z = 1.988
IN
+ 0.008
IN
/ - 0.024
IN
– Undo the screws of the stop plate (left side of the cylinder)
1
and
2
and apply
Loctite 242 to the threads. Then mount both screws but do not tighten them yet.
– Set preselected value on depth gauge and fix.
– Swifel control flap upwards and hold depth gauge into cylinder as shown in the
illustration.
– Control flap must rest against depth gauge.
– Allow bump plate
3
to rest against retaining bracket
4
.
5
Z
X