Royal Enfield SPRING FRAME O.H.V. 250cc CLIPPER 1954 Workshop Maintenance Manual page 17

ROYAL ENFIELD WORKSHOP MANUAL
Slacken back the compressing tool and
release the springs.
Withdraw the valve and place its springs, top
spring collar (and bottom collar if it is loose)
and split conical collets together in order that
they may be re-assembled with the valve from
which they were removed.
Deal similarly with the other valve in the
head. If the valve will not slide easily through
the valve guide, remove any slight burrs on the
end of the valve stem with a carborundum stone.
If the burrs are not removed and the valve is
forced out, the guide may be damaged.
8. Removal of Rockers
See Subsection 6.
9. Removal of Valve Guides
To remove the valve guides from the head
two Special Tools are required which can easily
be made.
The first is a piece of tube with an internal
bore of not less than 7/8 in.
The second is a mandrel about 4 in. long,
made from 9/16 in. dia. bar with the end turned
down to 11/32 in. dia. for 1/2 in.
Support the cylinder head on the tube, which
fits over the collar of the valve guide. Using the
mandrel, force the guide out of the head with a
hand press or by using a hammer.
To fit a new guide, support the head at the
correct angle and use a hand press and the same
mandrel. If a hand press is not available and the
guide is replaced by a hammer, use the mandrel
to prevent damage to the guide which is of cast
iron and must be treated with great care.
It is necessary to re-cut the valve seat and
grind in the valve after a guide has been
replaced.
10. Removal of Cylinder Barrel.
Remove the Cylinder Head (Subsection 6).
Put the Piston at bottom dead centre.
Undo five nuts and lift the barrel off.
When replacing the cylinder, clean off the
joint faces and fit a new paper joint washer. See
that the oil hole in the paper joint is opposite the
oil passage through the crankcase and cylinder.
11. Removal of Piston
Remove the cylinder head and cylinder
barrel. (Subsections 6 and 10.)
With the tang of a file remove one of the
wire circlips retaining the gudgeon pin.
Extract the gudgeon pin using Special Tool
No. E.5477, having first marked the pin so that
it, and the piston, may be replaced the same way
round.
Section C3 Page 4
During this operation put a piece of clean rag
in the top of the crank case to prevent foreign
matter getting in. In particular, take care not to
drop the circlip in the crankcase.
12. Decarbonising
Having removed the cylinder head, as
described in Subsection 6, scrape away all
carbon gently and avoid scoring the combustion
chamber or the valve seats. Be careful too not to
injure the joint face which beds down on to the
head gasket.
Scrape away all carbon from the valve heads
and beneath the heads, being careful not to
damage the valve faces. In cleaning the top of
the piston remember that it is made of
aluminium alloy and easily damaged.
If the piston rings are removed, the grooves
can be cleaned out and new ones fitted. For
cleaning the grooves a suitable tool is a piece of
broken ring thrust into a wooden handle and
filed to a chisel point.
While the cylinder and piston are not in
position, cover the crankcase with a clean cloth
to prevent the ingress of dust and dirt of all
kinds. Do not, of course, attempt to scrape the
carbon from the piston when the mouth of the
crankcase is open.
13. Grinding-In Valves
Wipe the valve faces clean and examine
them carefully. If they are at all pitted, have the
faces re-cut. Pay similar attention to the valve
seats in the head; excessive grinding will form a
pocket and the gas flow will be restricted. The
angle of the valve face should be 45 degrees to
the axis of the valve stem.
To grind a valve, smear the seating with a
little grinding-in compound, place a light, short
coil spring over the valve stem and beneath the
head, insert the valve into its appropriate guide,
press it on to the seat using a tool with a suction
cup or one which grips the valve stem and with
a backwards and forwards rotary motion, grind
it on to its seat. Frequently lift the valve and
move it round so that an even and true seating is
obtained. Continue grinding until a bright ring is
visible on both valve and seating.
14. Reassembly after Decarbonising.
Before building up the engine, see that all
parts are scrupulously clean and place them
conveniently to hand on a clean sheet of brown
paper.
It is advisable to fit a new gasket to the
cylinder head and a new paper washer at the
cylinder base. Make sure that there is a hole in
the latter registering with the oil feed to the back
of the cylinder.