A.J.S. 16, Instruction Book

Page: 36 / 104

Re-fit piston by:
Introduce piston over connecting rod, so that slit in piston faces to the front of the
machine.
Introduce gudgeon pin in piston and pass it through connecting rod small-end bush and
centralise it.
Re-fit circlips. (Use special pliers). Use rotary action when bedding circlips in their
grooves and make sure each circlip lies snugly in its groove. This is essential otherwise
considerable damage will result.
Re-fit cylinder barrel by:
Take new cylinder base washer. Coat one side with liquid jointing compound and
apply it to cylinder base.
Smear cylinder bore and piston with clean engine oil.
Space piston rings so that the gaps are evenly spaced at 120° to each other.
Gently fit barrel over piston and carefully compress each ring in turn, with the fingers,
as it enters the chamfered mouth of the barrel.
Remove rag from crankcase throat.
Replace cylinder barrel holding down nuts, screwing each down, in turn, bit by bit, till
all are fully home.
CAM C O N T O U R
On the flanks of the cams are quietening curves which are very slight inclines from the
base circles to the feet of the humps.
Therefore, it is necessary to ensure the tappet ends are on the base circles when checking
valve clearances and valve timing.
It is for this reason valve clearances must be checked when the piston is at the top of its
compression stroke, at which position both tappets are well clear of the quietening
curves.
VALVE T I M I N G
Taken with valve ·001" off its seat.
Inlet valve timing
Inlet valve opens 36° before top dead centre—350 c.c. models.
Inlet valve opens 18° before top dead centre—500 c.c. models.
Inlet valve closes 51° after bottom dead centre—350 c.c. models.
Inlet valve closes 69° after bottom dead centre—500 c.c. models.
Exhaust valve timing
Exhaust valve opens 50° before bottom dead centre—All models.
Exhaust valve closes 30° after top dead centre—All models.
(See page 96 for particulars of special timing disc graduated in degrees.)
Camshaft timing marks
Use mark 1 for exhaust cam—all touring models.
Use mark 2 for inlet cam—500 c.c. touring and competition models.
Use mark 2 for exhaust cam—all competition models.
Use mark 3 for inlet cam—350 c.c. touring models.
When checking the valve timing the tappet clearances must be set to ·016" so that the
tappets may be well clear of the quietening curves of the camshafts.
The timing gears are marked to facilitate their replacement.
To re-set the valve timing, by using the marks on the gears, proceed as follows:—
Turn over the engine till the mark on the small timing pinion is in line with the centre
of the inlet (rear) camshaft bush. Insert the inlet camshaft so that the No. 2 or No. 3
mark on it is in mesh with the mark on the small timing pinion, according to model.
Rotate the engine in a
forward direction till the mark on the small timing pinion
is in line with the centre of the exhaust (front) camshaft bush. Insert the exhaust
camshaft so that the No. 1 mark on it is in mesh with the mark on the small timing
pinion.
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