Silencer
The silencer is fitted with a detachable end cap held in position by a single central nut
inside the exhaust opening. This is easily unscrewed and the cap and internal baffle
removed for cleaning. Note when replacing the baffle unit that the copper sealing
ring is in position before replacing the end cap. The two plain washers and one
spring washer must be replaced on the stud before tightening the central locking nut.
Removal of Cylinder
First turn off the petrol and detach the petrol pipe by means of the hexagon on top of
the float chamber. The plastic petrol pipe is clipped to the petrol tap union and
should not be disturbed. Next remove the carburetter from its stub at the rear of the
cylinder by releasing the clip bolt by means of which it is attached. The exhaust pipe
must also be disconnected by releasing the union nut at the front of the cylinder barrel
by means of the special “C” spanner included in the tool kit. If this nut should prove
unduly obstinate, a few drops of penetrating oil should be applied to the threaded
portion immediately above the nut and a little time should be allowed for this to act
before attempting to unscrew the nut. Disconnect the high-tension lead from the
sparking plug and unscrew the latter.
The cylinder head and barrel are attached to the crankcase by means of four long
studs, and when the four nuts on the top of the cylinder head are removed, the head
can easily be lifted clear. Removal of the cylinder barrel is greatly facilitated if the
two petrol tank front locking bolts are unscrewed so that the tank can be raised
slightly. Take care when removing the barrel to support the piston as it emerges from
the end of the bore in order that it may not be damaged as it falls clear.
Piston
Place the cylinder head and barrel on one side on a bench and examine the piston. It
should not be necessary to remove this from the connecting rod, but if it should be
desired to do this for any reason, first remove the circlip from one end of the gudgeon
pin using a pair of pointed-nose pliers or some suitable instrument to lever the circlip
out. Then holding the piston firmly in the hand, tap the gudgeon pin out from the
other end. If it is too tight to move, it can be released by warming the piston by
means of a rag soaked in hot water and wrung out. Application of this rag will cause
the aluminium alloy of the piston to expand more than the steel gudgeon pin, thus
releasing the latter which can then be freely pushed or tapped out.
Scrape off any carbon which has accumulated on the crown of the piston, taking
care not to damage the relatively soft surface of the metal itself, and after removing
all the carbon, polish lightly with fine emery cloth if desired and finally wipe clean
with an oily rag.
Piston Rings
Now examine the piston rings noting that these are located in their grooves by means
of pegs which engage in the piston ring gaps. If in good condition, the rings will be
found to present a uniformly smooth metallic surface over their entire peripheries,
and if they are in this condition and obviously have a certain amount of “springiness”
as evidenced by the fact that their free gap is considerably greater than the closed gap
when in the bore, they should not be disturbed.
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