Checking The Piston - Yamaha 25BMH Service Manual

POWR
CRANKSHAFT AND CYLINDER BODY
C C C C y y y y l l l l i i i i n d n d n d e e e e r r r r n d
bor r r r e e e e bo
bo bo
d d d d i i i i a a a a m m m m e e e e t t t t e e e e r r r r
" " " " D D D D " " " "
T T T T a a a a p p p p e e e e r r r r li li li lim m m m i i i i t t t t
" " " " T T T T " " " "
O O O O u u u u t t t t o o o o f f f f r r r r oun ound d d d oun oun
li li li lim m m m i i i i t t t t " " " " R R R R " " " "
D D D D = = = = M M M M a a a a x x x x i i i i m m m m u u u u m m m m D D D D 1 1 1 1 , , , , D D D D 2 2 2 2 , , , , D D D D 3 3 3 3 , , , , D D D D 4 4 4 4 , , , , D D D D 5 5 5 5 o o o o r r r r D D D D 6 6 6 6
T T T T = = = = ( ( ( ( M M M M ax ax ax axi i i i m m m m u u u u m m m m D D D D 1 1 1 1 o o o o r r r r D D D D 2 2 2 2 ) ) ) ) – – – – ( ( ( ( M M M M i i i i n n n n i i i i m m m m u u u u m m m m D D D D 5 5 5 5 o o o o r r r r D D D D 6 6 6 6 ) ) ) )
R R R R = = = = M M M M ax ax axi i i i m m m m u u u u m m m m ( ( ( ( D D D D 1 1 1 1 – – – – D D D D 2 2 2 2 ) ) ) ) o o o o r r r r ( ( ( ( D D D D 3 3 3 3 – – – – D D D D 4 4 4 4 ) ) ) ) o o o o r r r r ( ( ( ( D D D D 5 5 5 5 – – – – ax
D D D D 6 6 6 6 ) ) ) )
A: 15 mm (0.59 in) below the cylinder top
B: 25 mm (0.98 in) above the exhaust port
C: 100 mm (3.94 in) below the scavenging port

CHECKING THE PISTON

1. Check:
• Piston wall
Wear/scratch/damage → Replace.
2. Check:
• Piston head
• Piston ring groove
Carbon deposits → Clean.
CAUTION:
Take care not to scratch or cut the alumi-
num surface.
5-32
S S S S t t t t a a a a n n n n d d d d a a a a r r r r d d d d
7 7 7 7 2 2 2 2 . . . . 0 0 0 0 0 0 0 0 - - - - 7 7 7 7 2 2 2 2 . . . . 02 02 02 02 mm mm mm mm 72 72 72. . . . 1 1 1 1 0 0 0 0 mm 72
( ( ( ( 2 2 2 2 . . . . 8 3 8 3 4 4 4 4 6 6 6 6 – – – – 2 2 2 2 . . . . 8 3 8 3 5 5 5 5 4 4 4 4 ( ( ( ( 2 2 2 2 . . . . 8 8 8 8 386
8 3 8 3 8 3 8 3
i i i i n n n n ) ) ) )
0 0 0 0 . . . . 0 0 0 0 8 8 8 8 mm
– – – –
( ( ( ( 0 0 0 0 . . . . 0 0 0 0 0 0 0 0 31
0 0 0 0 . . . . 0 0 0 0 5 5 5 5 mm
– – – –
( ( ( ( 0 0 0 0 . . . . 0 0 0 0 0 0 0 0 20
E
W W W W ea ear r r r li li li lim m m m i i i i t t t t
ea ea
mm mm mm
386 i i i i n n n n ) ) ) )
386 386
mm mm mm
31 i i i i n n n n ) ) ) )
31 31
mm mm mm
20 i i i i n n n n ) ) ) ) 20 20