A.J.S. 16, Instruction Book

Page: 31 / 104

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 loss of power, heavy petrol consumption or generally reduced performance.
When undertaken, unless it is thought necessary to inspect the piston and rings, the
cylinder barrel/s are best left undisturbed.
The various stages in decarbonisation are described.
SINGLE CYLINDER MODELS
TO REMOVE THE ROCKER B O X
Remove the petrol tank.
Remove the three nuts and fibre washers retaining the rocker box side cover and take
away the cover.
Disconnect the oil pipe feeding oil to the rocker box.
Turn over engine until both valves are completely closed.
Remove engine steady bracket by removing bolt from frame clip and nuts and washers
from the rocker box bolt extensions.
Remove the nine bolts retaining rocker box to cylinder head.
Disconnect valve lifter cable.
Tilt upward the right hand side of rocker box and extract the two long pushrods. Lay
these aside so they may be identified and replaced in their original position.
The rocker box may then be lifted off.
TO REPLACE T H E ROCKER B O X
Carefully clean the top of cylinder head and lower face of rocker box.
Revolve engine until both tappets are down, i.e., the top dead centre of firing stroke.
Lay the composition jointing washer on cylinder head.
This must be faultless. If
necessary, renew.
Lay the rocker box in position then slightly raise the right hand side to allow the long
push rods to be inserted into their original respective positions.
Insert all nine rocker box fixing bolts and note that the bolt with short head is in the
centre right hand position and the bolts with threaded extensions are fitted one each
side of the central short head bolt.
Tighten each bolt in turn bit by bit until all are fully home.
Replace the engine steady stay.
Turn engine over several times to ensure parts have bedded home.
Re-fix valve lifter cable.
Re-fix rocker box oil pipe union nut using two spanners to ensure that the union
screwed into rocker box does not turn while the nut is being tightened.
Check tappet clearances and re-set if necessary.
Inspect rubber fillet on rocker box side cover and renew if not perfect.
Replace the side cover ensuring that a fibre washer is fitted under each of the three
retaining nuts.
Beware of over tightening these nuts, the joint being made by the rubber fillet excessive
pressure is not necessary.
TO REMOVE T H E CYLINDER HEAD
Remove
The petrol tank.
The sparking plug. See note on page 38.
The rocker box.
Remove t h e 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.
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