N-Zeta 501/01, Workshop Manual

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To dismantle the cylinder barrel, it is necessary to first unscrew the studs
fastening the cylinder barrel to the crankcase. Thread two nuts onto the studs and
tighten them onto each other. Now unscrew them together with the stud by turning
the bottom nut. In this manner, remove all four studs. fig.5
To free the cylinder barrel, carefully lever it using screwdrivers after having
first brought the piston to BDC with the kick-starter pedal. Having removed the
cylinder barrel, cover the hole in the crankcase under the piston with a clean cloth; it
is now possible to proceed to decoke, to take off the piston or to replace the small
end bush. Using the S-3 special pliers or 3 tin foils, remove the piston rings. The
piston should be removed only when it is to be replaced or when the gudgeon pin or
small end bush have to be replaced. For the original piston with the pressed in
gudgeon pin / scooters 501/01
– 03 up to engine Nº. 132252/ puller S-38 should be
used for extracting the gudgeon pin. For the new piston with floating pin / model
501/05 and 502/00
– 01/ use the locating pins S-3 and push out the gudgeon pin
with light pressure by hand. When dismantling the piston, first remove the two circlips
securing the gudgeon pin. Never drive out the gudgeon pin as there is danger of
bending the connecting rod.
Piston
For scooter model 501/01, 03 and 05, new piston Part Nº. 356-12-241 should
be employed only. Together with this piston, setting of the 2924 M 13 carburettor has
to be modified as indicated. Pistons are marked on the top with letters according to
the manufacturers dimensions determining their assemble with cylinder barrels and
gudgeon pins. The marking consists of two letters, the first of which A, B, C
determines the piston diameter and thereby its suitability for the corresponding
cylinder barrel marking. The second letter Y, Z marks the dimensions of the gudgeon
pin diameter.