KTM 300 EXC, Repair Manual

Page: 156 / 289

18 ENGINE
154
Guideline
Distance
B
50 mm (1.97 in)
Piston - diameter (All 250 models)
Size I 66.340… 66.350 mm (2.61181…
2.6122 in)
Size II 66.351… 66.360 mm (2.61224…
2.61259 in)
Piston - diameter (All 300 models)
Size I 71.940… 71.950 mm (2.83228…
2.83267 in)
Size II 71.951… 71.960 mm (2.83271…
2.83307 in)
Info
Piston dimensions
1
are marked on the piston head.
18.4.13 Checking the piston ring end gap
303012-10
–
Remove the piston ring from the piston.
–
Place the piston ring in the cylinder and align with the piston.
Guideline
Below the upper edge of the cylinder 20 mm (0.79 in)
–
Measure end gap
A
with a feeler gauge.
Guideline
Piston ring - end gap
Ring 1
≤
0.40 mm (
≤
0.0157 in)
Ring 2
≤
0.40 mm (
≤
0.0157 in)
» If the end gap is greater than the specified measurement:
–
Check/measure the cylinder. ( p. 147)
» If cylinder wear lies within the specified tolerance:
–
Change the piston ring.
–
Mount the piston ring with the marking facing toward the piston head.
18.4.14 Piston/cylinder - measuring the mounting clearance
303083-10
(All 250 models)
–
Check/measure the cylinder. ( p. 147)
–
Check/measure the piston. ( p. 153)
–
The smallest piston/cylinder mounting clearance equals the smallest cylinder
bore diameter minus the largest piston diameter. The largest piston/cylinder
mounting clearance equals the largest cylinder bore diameter minus the small-
est piston diameter.
Guideline
Piston/cylinder - mounting clearance
New condition 0.050… 0.074 mm (0.00197…
0.00291 in)
Piston/cylinder - mounting clearance
Wear limit 0.10 mm (0.0039 in)
303015-10
(All 300 models)
–
Check/measure the cylinder. ( p. 147)
–
Check/measure the piston. ( p. 153)
–
The smallest piston/cylinder mounting clearance equals the smallest cylinder
bore diameter minus the largest piston diameter. The largest piston/cylinder
mounting clearance equals the largest cylinder bore diameter minus the small-
est piston diameter.