Piston - Yamaha JT1 Series Service Manual

C. Checking the Piston Rings
1) Measuring piston ring wear ,Put the ring into
the cylinder so that the ring is parallel to the
cylinder bottom edge. and then measure the
end gap with a feeler gauge(Fig ·3-5-4)
The end gap should be between 0.t5 and 0.35
mm. (0.006---0.014") for both No.1 and No.2
rings
2) Removing carbon
ENGINE -
Piston
Fig. 3-5-4
Carbon on the piston rings and
in
the ring grooves will make the rings stick in the piston. thus causing gas
blow -by
Remove the rings from the piston. and clean the carbon from the rings and ring grooves. using the
end of an old ring' as a scraper.
3-6 Piston
The piston is made of a high-silicon aluminum alloy.
A Checking and Correcting the Piston to Cylinder Wall Clearance
1) Measuring piston clearance
Piston clearance is the difference between
the minimum cylinder bore diameter and the
maximum outside diameter of the piston As
described in
4-3
Cylinder, piston clearance
should be 0.040-0.04Smm (0 0016-0.0018")
To determine the maximum piston diameter,
measure the piston with a micrometer at right
angles to the skirt 10 mm. (3/8 in.) from its
bottom edge. (Fig 3-6-1)
2) Checking and correcting scratches on the
piston
A piston showing signs of seizure will result
in noise and loss of engine power. It will also
cause damage to the cylinder wait
If
a piston that has seized is used again
without correction ,another seizure will develop
in the same area. Lightly sand the seizure
"high spot" on the piston with wet #400
sand paper until smooth.
- 1 9 -
Fig. 3-6-1
Fig 3-6-2