DECARBONISING.
1. Removal of Cylinder Head.
Decarbonising will normally be necessary
approximately every 2,000 miles and can be carried
out without removal of the engine from the frame.
First remove the petrol pipe and the four bolts
underneath the tank which secure it to the brackets
and remove the tank. (If necessary the front saddle
attachment bolt must be removed.) Next remove the
cover over the valve gear, the carburetter, exhaust pipe
and silencer. Remove the rocker bearing caps and
rockers and lift the push rods out of their tubes (if the
collar on the exhaust push rod will not clear the joint
between the cylinder head and the barrel, leave this
rod in position until after the head has been lifted off).
The cylinder head can then be lifted off after
unscrewing the four nuts which secure it to the
cylinder.
2. Removal of Cylinder and Piston.
While it is not strictly necessary to remove the
cylinder barrel and piston, this should preferably be
done so that the condition of the piston, rings and
big-end bearing can be examined. To remove the
cylinder barrel after removal of the head, unscrew the
four cylinder base nuts, (On the 350 there is a fifth
nut inside the tappet chest between the two
tappets). Disconnect the exhaust lifter cable from the
handlebar lever, place the piston at the bottom of its
stroke and lift the barrel off. To remove the piston,
push out the gudgeon pin, after removal of the wire
retaining clips with a suitable tool (such as the tang
end of a small file) and lift the piston off the rod. Mark
the piston so as to ensure reassembling the same way
round.
3. Removal of Valves.
To remove the valves from the cylinder head,
first lift off the hardened end caps from the valve
stems. If these have stuck, they can be removed by
compressing the spring slightly and gripping the end
cap in a vice (see Fig. 1 ). Then compress the valve
springs with a suitable compressor, lift out the split
4. Removal of Carbon.
Remove carbon from the valves, ports and
combustion chamber by scraping or by immersion in a
solution of 4 ozs. of commercial potash to a gallon of
water. Carefully remove the piston rings. Remove
carbon from the ring grooves and the top of the piston
by carefully scraping, taking care not to dig into the
aluminium. On no account allow potash solution to
come into contact with an aluminium piston.
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