Piston; Cleaning; Inspection - Yamaha 50G Service Manual

POWR

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.
Piston diameter:
Standard:
50, 60, 70 hp:71.945 ~ 71.970 mm
75, 80, 90 hp:81.935 ~ 81.960 mm
2. Using the measured cylinder bore
diameter in thrust directions, subtract
the piston diameter measurement from
the cylinder bore diameter measure-
ment.
Piston clearance:
50, 60, 70 hp: 0.050 ~ 0.055 mm
75, 80, 90 hp: 0.060 ~ 0.065 mm
If this clearance is not within the specifi-
cations, replace the piston with stan-
dard or oversize and/or rebore the
cylinder.
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)
* Except for USA
5-8
E
(2.8325 ~ 2.8335 in)
(3.2258 ~ 3.2268 in)
(0.0020 ~ 0.0022 in)
(0.0024 ~ 0.0026 in)