Checking Valve Seat Wear; Valves Check; Standard Diameter; Minimum Allowed Diameter - PIAGGIO 500 cc Service Manual

Thermal unit and timing system

Checking valve seat wear

- Remove any carbon deposits from the valve seat.
- Check the width of the imprint on the valve seat "V" by
means of Prussian blue.
- Measure the inside diameter of each valve guide.
- Perform the measurement according to the thrust
direction of the equalizer at three different heights.
Standard value: 1 - 1.3 mm
Limit allowed: 1.6 mm
- If the imprint width on the valve seat exceeds the
recommended limits, regrind the seats with the 45°
cutter and then recondition them.
- In case of excessive wear or damages, replace the
head.

Valves check

- Check the valve stem diameter in the three points
shown in the figure.

Standard diameter

Intake: 4.987 - 4.972 mm
Exhaust: 4.975 - 4.960 mm

Minimum allowed diameter

Intake: 4.96 mm
Exhaust: 4.945 mm
- Calculate the valve - valve guide clearance.
- Check the valve stem deviation by putting it on a "V"
surface. Measure the deformation by means of a dial
gauge.
Limit allowed: 0.01 mm
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