Yamaha MM700A, Manual, Page: 115 / 282

ENGINE
109
conditions, the engine may be experiencing preignition or
detonation. Both conditions are discussed in Chapter
Two.
CAUTION
Do not clean piston skirts or ring lands us-
ing a wire
The wire brush removes
aluminum that will increase piston
The brush also rounds the corners
the ring lands causing decreased support
for the piston rings.
10. If the previous inspection procedures indicate the pis-
ton is in good condition, measure the piston outside diam-
eter as described under
Clearance in this
chapter.
Clearance
The following procedure requires using highly special-
ized and expensive measuring tools. If such equipment is
not readily available, have the measurements performed
by a dealership or machine shop. Always replace all pis-
tons as a set.
1. Measure the outside diameter of the piston with a mi-
crometer approximately 10
in.) above the bot-
tom of the piston skirt, at a angle to the piston pin
(Figure 37, typical).
2. Clean the cylinder completely. Wash the cylinder bore
with soap and water to remove oil and carbon particles.
Thoroughly clean the cylinder bore before attempting any
measurement to prevent inaccurate readings caused by
debris.
3. Measure the cylinder bore with a bore gauge or tele-
scoping gauge (Figure
Then measure the bore gauge
or telescoping gauge with a micrometer to determine the
bore diameter. Measure the cylinder bore at three vertical
locations in the cylinder, in line with the piston pin and at
to the pin as shown in Figure 39, typical. If the bore is
greater than specifications (Table 2 or Table 3), replace
the cylinder.
4. Piston clearance is the difference between the maxi-
mum piston diameter and the minimum cylinder diameter.
Refer to Table 2 or Table 3 for the specified clearance. If
the piston clearance is greater than specified, replace the
piston.
NOTE
Wear is monitored by checking the pis-
ton-to-cylinder clearance. When the clear-
ance is excessive, measure the clearance
again using a newpiston.
clearance is
still excessive with new piston, the