KTM 250 SX - Manual (Page 62)

Mounting 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.
Adjusting dimension „X“
Dimension „X“ is the dimension from upper edge of piston to upper edge
of cylinder with cylinder under low tension and piston in TDC position.
The 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 .
– Set the piston to TDC, and apply a sliding gage or straight-edge to the
cylinder. Now, check the distance between the piston's upper edge
and the sliding gage. This distance should be from 0 mm to 0.10 mm
at the most. It can be corrected, if necessary, by adding or removing
of cylinder-base gaskets.
! CAUTION !
T HE PISTON MUST NOT PROTRUDE BEYOND THE CYLINDER ' S UPPER EDGE .
– Mount the 2 remaining collar nuts at the cylinder base, and tighten
each of the 4 collar nuts to 35 Nm (27 ft.lb.).
6-7C
Dimension „X“ = 0 mm + 0,1 mm
X