A.J.S. 16MS, Instruction Book

Page: 28 / 94

DECARBONISATION
Instead of the usual stipulated mileage interval between periods of decarbonisation, it is
recommended that this is undertaken only when the need for same becomes apparent
because of excessive pinking, loss of power or generally reduced performance. When
undertaken, unless it is thought necessary to inspect the piston and rings, the cylinder
barrel is best left undisturbed. The various stages in decarbonisation are described
below.
TO REMOVE THE CYLINDER HEAD
Remove
The petrol tank.
The sparking plug.—See note below.
The rocker box.
Remove the exhaust system by :
Remove nut, and washers, retaining exhaust pipe to its stay.
Remove nut, and washers, retaining silencer to Its stay.
Remove complete exhaust system, by pulling away from stays and then downwards.
from the exhaust port In cylinder head.
Remove carburetter by:
Unscrew two carburetter retaining nuts.
Take away carburetter and rest on saddle.
Remove
The four bolts retaining cylinder head to barrel, and head is free to be taken away.
While doing this the push rod cover tubes will come away with the head.
Note
If the sparking plug resists removal, do not use force but brush paraffin round the
body and leave for a time to soak before making further effort.
TO REMOVE AND REPLACE THE VALVES AND GUIDES
Remove the cylinder head.
Remove the valve springs by inserting a finger in the spring coil and sharply pull upward.
Th2 top spring collar and split collet can then be removed leaving the valve free to be
withdrawn.
A sharp light tap on the valve collar may be necessary to free the taper split collet. It
will be observed that the valve spring seat has a raised impression on Its under side
which registers with a hole drilled on the valve guide boss to ensure accurate positioning.
To remove an inlet valve guide, thoroughly clean protruding end of guide to be removed.
Apply gentle heat and press guide downwards. To remove an exhaust valve guide,
apply gentle heat, press the guide upwards sufficiently to permit removal of the external
circlip. Then, clean the top of the guide, and press downwards to remove. Re-heat
when replacing and see that correct projection is obtained, viz. ½" Also see that oil
hole in guide is in correct alignment.
TO REPLACE A VALVE
After cleaning valve guide bores, smear each valve stem with clean oil, insert, and apply
top collar and split collet.
Then apply the valve springs which although possible to fit by hand are more easily
manipulated with a special compressor tool Part No. 018276 illustration 8. To operate
this tool apply the top end of the valve spring to its groove in the top cap, then insert
a short rod (one of the rocker box fixing bolts suits admirably) through the holes in this
tool and the valve spring coils and pull outward and upward until the ends of the prong
of the spring can be rested on the seat, then press down with the fingers. Withdraw
the bolt or rod when the compressor lies against the cylinder head, retaining pressure
with the fingers until the bolt has been withdrawn and the tool removed, when the spring
can be readily pushed down to its proper location with the prongs laying flat upon the
seat.
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