Yamaha 50G, Service Manual

Page: 79 / 204

5-8
POWR
E
INSPECTION
G62001-0*
PISTON
CLEANING
1. Using a gasket-scraper, remove the car-
bon from the piston top.
2. Using a broken ring, clean the ring
grooves.
3. Using a soft brush and solvent, thor-
oughly clean the piston. If necessary,
use 600 ~ 800 grit wet-or-dry sandpaper
to remove score marks or varnish.
INSPECTION
1. Using a micrometer, measure the pis-
ton diameter at right angles to the pis-
ton-pin center line, 10 mm (0.4 in)
above the bottom edge.
2. Using the measured cylinder bore
diameter in thrust directions, subtract
the piston diameter measurement from
the cylinder bore diameter measure-
ment.
If this clearance is not within the specifi-
cations, replace the piston with stan-
dard or oversize and/or rebore the
cylinder.
* Except for USA
Piston diameter:
Standard:
50, 60, 70 hp:71.945 ~ 71.970 mm
(2.8325 ~ 2.8335 in)
75, 80, 90 hp:81.935 ~ 81.960 mm
(3.2258 ~ 3.2268 in)
Piston clearance:
50, 60, 70 hp: 0.050 ~ 0.055 mm
(0.0020 ~ 0.0022 in)
75, 80, 90 hp: 0.060 ~ 0.065 mm
(0.0024 ~ 0.0026 in)
Oversize piston:
50, 60, 70 hp:
*1st 72.25 mm (2.844 in)
2nd 72.50 mm (2.854 in)
75, 80, 90 hp:
*1st 82.25 mm (3.238 in)
2nd 82.50 mm (3.248 in)