oil on the valve stems and also inside each guide before assembly.
Removing the cylinder and piston. With the cylinder head removed, the
barrel can be raised vertically to clear the holding down studs. Before
doing so, position the engine with the piston on the top of its stroke,
have available a piece of clean rag. Raise the cylinder sufficiently to
enable the rag to be put into the throat of the crankcase (under the
piston) as a precaution against a broken ring falling into the crankcase.
then lift the cylinder clear of the four studs passing through it. Make a
mark inside the piston to indicate front.
The gudgeon pin is a sliding tit in both the piston and connecting rod.
Use round nose pliers to compress and extract the circlip (it is immaterial
which one is removed) then push out the gudgeon pin and lift the piston
off the connecting rod.
Do not disturb the piston rings unless absolutely necessary.
If new piston rings are used, they are ready for fitting, as the ring gap
is allowed for during manufacture,
The top compression ring is chromium plated and has a slightly tapered
extension. When new, the word TOP is etched on the ring face to indicate
which way it should be fitted. Fit first the scraper or oil control ring,
then the two compression rings, to avoid breakage do not expand these
rings unnecessarily.
Refitting the piston. Before refitting the piston apply a little oil to the
gudgeon pin, also to the bosses for the gudgeon pin in the piston. Place
the piston over the connecting rod in the same way as it was removed.
or in accordance with the marking made, and then introduce the gudgeon
pin through the piston, connecting rod and piston bosses.
It is vitally important to correctly locate the gudgeon pin circlip, and
a little extra care and time should be devoted to this most simple and
important operation. Use round-nosed pliers to introduce the circlip into
its groove, using a rotary motion then verify that the circlip is correctly
located.
Refitting the cylinder barrel. Fit a new cylinder base gasket, after
removing broken pieces of the old one. Use a little jointing compound on
the base of the cylinder and stick a new gasket to it, no jointing com-
pound should be on the crankcase face. Set the piston ring gaps at 120°.
pass the cylinder over the four long studs and lower it gently at the same
time compressing each piston ring in turn with the fingers, until the
cylinder has passed the scraper ring when it can be lowered on to the
crankcase.
NOTE—Some clean rag under the piston to fill the throat of the crank-
case will safeguard against a broken piston ring falling into the crankcase.
Refitting the cylinder head. The cylinder head gasket also acts as an oil
seal for the push rod tunnels, consequently it must be in good order if it
is to be used again. To avoid the possibility of subsequent attention a new
gasket is desirable.
This gasket is neither symmetrical nor reversible and it must be placed
on the cylinder in the correct way,
A study of the cylinder barrel face will show an elongated hole (where
the push rods operate).
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