TM RACING 250 EN, Workshop Manual

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24
top ring
top ring
5
4
3
6
N
1
2
1
2
3
3
ENGINE DISASSEMBLY
Insert the piston (5) on the cylinder (4) so that the ring (3) is positioned
level.
With a thickness gauge (6) check the “Thermal GAP” ring opening distance
(3) which must be 0,60 ÷ 0,65 mm (0,0236 ÷ 0,0255 in).
If necessary, using a file, restore the measurement and repeat the check
procedure.
2.8.3 Ring mounting
Clean the housing (1) of the rings on the piston from any carbon deposits.
NOTE: Apply engine oil on the rings before mounting them on the piston.
Be careful not to scratch the piston when re-mounting.
Do not widen the rings excessively during mounting, so that they
are not damaged.
Install the rings (2 and 3) positioning them with the face engraved with an
“N” on the upper part.
Check that the rings rotate freely around the piston and are not obstructed.
Position the open part of the ring (2) and the adherent part of the ring (3)
so that they are 180° apart as indicated in the figure, before re-mounting
the piston in the cylinder.
2.8.4 Piston replacement
Remove the piston and cylinder as described in the relative paragraph.
2.8.5 Piston replacement with intact cylinder
Check the integrity of the cylinder barrel, if the barrel is intact and not
scored, clean with scotch brite and wash.
Order the piston and rings of the same size as the original equipment pis -
ton:
tolerance between cylinder and piston 0,09 mm (0,0031 ÷ 0,0035 in).
Fit the rings on the piston as described in the relative paragraph.