The grinding-in process consists in coating the bevelled face of the valve
with a small quantity of valve-grinding paste-applied on the end of a match-
stick-reinserting the valve in its guide and partially rotating it backwards
and forwards on its seating by means of a screwdriver. Here wse come ro
the secret of good valve grinding. The valve should be raised from its
seating every few recipocrations and given a half turn in order that the
grinding compound may spread itself evenly over the whole surface.
If
this
is not done there is the possibility that minute circular grooves will b'e cut
into the face of both the valve and its seating, which will absolutely prevent
one from obtaining a good gastight fit. Probably the most convenient way
of carrying out this periodical lifting is to obtain a light coil spring (similar
to the valve spring but much lighter), and insert it into the valve port beneath
the valve head. When pressure is released on the screwdriver the valve
will pop up, when it can easily be rotated into
a
fresh position.
It is not necessary to continue grinding the valves once the faces of both
valve and seating have assumed a clean,
seven, matt-surfaced appearance.
A
polished surface must not be expected and is quite unnecessary. If the
engine has been run for a long period without being decarbonised, the valve
may be badly
"
pitted "-that is to say, it will have a number of small black
spots or depressions on its face. Should these depressions be at all excessive
or deep, it is best to have the valve face trued up on a special machine at a
garage. This will prevent needless grinding away of the valve seating in the
cylinder head-a matter of importance, as it cannot be renewed. Any valves
which are distorted should immediately be replaced by new ones. To
attempt to grind them in will only produce extensive damage to the seating.
After each valve is ground in it should be withdrawn and carefully
washed in paraffin, and, what is ,equally important, the valve seating and the
surrounding valve port should also thoroughly be cbeaned with a rag
moistened with paraffin. Do not wash out thme valve ports with petrol or
paraffin or some of the grinding compound will find its way into the valve
guides or other working parts, and it is of the utmost importance that it
should be
prevent'ed from finding its way on to any of the working surfaces
of the engin'e, where extensive damage may be done.
Reassembling
the
Valves.
When you have satisfied yourself that all trac'e
of the grinding compound has been removed, the valves may be reassembled.
Care should again be taken to see that they are in their correct ports. Re-
assembly of the valve is not a difficult matter. After inserting the valve in its
guide and resting its head on the wood packing block, the valve spring may
be placed in position with the valve spring cap resting on top of it. Engage
a tool on the cap and depress the spring so as to expose very nearly the
whole of the groove in the upper 'end of the valve stem. Insert the two
conical cotters into the groove in the valve stem (small ends downwards, of
course) and gradually release the spring. Make surse that the cotters are
properly engaging in their grooves before dealing with the next valve. If the
valve cover saddles have been removed, do not forget to replace them in
position before reassembling the valves which are between the camshaft
bearing brackets, or you will find that these are in the way and that you
cannot
r'eplace the saddles.
PAGE
EIGHTEEN
D/I
To Next Page
Loading...
