KTM 250 1998 - 4.3 Crankshaft; 4.4 Piston; 4.5 Piston ring end gap

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4.3 Crankshaft
– When replacing the roller bearing, the inner crankshaft ring must also be rene-
wed. Heat the inner ring until it drops out of its seat.
– Before pressing the new inner ring in position, an intermediate plate must always
be placed between the two crank webs. The plate must be such as to be sup-
ported on both sides, so that the crankshaft remains free.
– Heat new inner ring to approx. 150° C and press into position. Make sure inner
ring is heated quickly.
!
CAUTION
!
N
EVER CLAMP THE CRANKSHAFT WITH A STUD OR WEB IN THE VICE
, AND NEVER TRY TO
KNOCK THE BEARING INNER RING FREE
. THE CRANKSHAFT WEBS MAY BE COM-PRESSED AND
THE CON
-RODPLUG AND BEARING MAY BE DAMAGES, THEREBY MAKING THE CRANKSHAFT
UNUSABLE
.
N
OTE: DISTANCE ADJUSTMENT OF THE MAIN BEARINGS IS NOT REQUESTED.
4.4 Piston
If a used piston is to remain in service then the following should be checked:
1. P
ISTON RUNNING SURFACE: Check for pressure marks (seizing marks) minor friction
marks can be removed with a fine abrasive stick.
2. P
ISTON RING GROOVES: The piston rings must not get jammed in the grooves. For
cleaning the grooves, use an old piston ring or abrasive paper (grain size 400).
3. T
HE PISTON RING LOCATING PINS must be firmly seated in the piston and must not
be worn out.
4. Check
PISTON RINGS for wear and check end gap.
4.5 Piston ring end gap
– Insert pisto ring into the cylinder and adjust. Piston ring must be approx. 10 mm
(1/2 inch) from top of cylinder.
– The end gap
B
can now be checked which a feeler gauge.
C
OMPRESSION RINGS: MAX. 0.40 MM (0.015 IN)
N
OTE: IF THE END GAP IS GREATER CHECK PISTON AND CYLINDER FOR WEAR. IF PISTON AND
CYLINDER WEAR ARE WITHIN THE PERMITTED TOLERANCE LIMITS
, REPLACE THE PISTON RING.
4.6 Checking cylinder for wear
Measure diameter of cylinder approx. 10 mm below top of cylinder edge. Check
diameter in several corresponding places to see if cylinder in worn oval. Cylinder
diameter - piston size
Cylinder diameter 250 Piston size
67,500 - 67,512 mm . . . . . . . . . . . . . . . . . . 1
67,513 - 67,525 mm . . . . . . . . . . . . . . . . . . 2
Cylinder diameter 300 Piston size
72,000 - 72,012 mm . . . . . . . . . . . . . . . . . .1
72,013 - 72,025 mm . . . . . . . . . . . . . . . . . .2
Cylinder diameter 380 Piston size
78,000 - 78,012 mm . . . . . . . . . . . . . . . . . . 1
78,013 - 78,025 mm . . . . . . . . . . . . . . . . . . 2
4
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10mm