Sunbeam ALPINE I SERIES: APLINE II SERIES, Руководство по ремонту, Страница: 63 / 413

WSM.124
Section B (Engine)
generally it will be found that these are better than
the valves as regards condition unless the engine
has been a very long time in service. It is quite
practicable to reface the valves and grind them in
on the seatings if the latter are in good order.
It is always better to replace a badly burnt or pitted
valve as extended refacing will bring it very low on
Its seating by reason of the consequent reduction in
the effective diameter of the vatve face, and "pocket­
ing" will result. (See Fig. 24). This condition is
detrimental to the running of the engine and will
cause overheating and loss of power. The valve face
should be machined only until it is just true and
clear of marks, to the standard angle of 45
°
for
inlet and exhaust. These angles are measured from
the top face of the valve head. Standard dimensions
of valves are given in the Data Section at the
beginning of this manual.
The refacing of valves must not leave too thin an
edge above the valve head seating. This applies
particularly to exhaust valves which must be
renewed If much refacing is needed.
A valve which has been refaced as described must
also be finally ground In on its seating (see
"VALVES-TO GRIND IN"). The seating must be
in good condition and the face not mor� than
·070' (1 ·78 mm.) in width.
VALVE SEATINGS
To recut
A damaged or slightly burnt seating may be refaced
with a 45
°
seating cutter as illustrated in Fig. 25.
A complete set of valve seat cutters can be obtained
from Messrs. V. L. Churchill (Tool No. R.G.316).
Individual items may be purchased separately if
required. It is most important that the cutter pilot
should be a good fit in the valve guide. If necessary
the valve guide should be renewed as the highest
possible concentricity must exist between the
seatings and valve guide bore (See "VALVE GUIDES
-TO
RENEW).
The seating should be recut with a 45
°
cutter until
all marks have disappeared.
NO lubricant is
required for this operation.
Fig. 28. Use
of valve seat cutting tool
Fig. 29, Use of
valve seat grinder
2nd
re-issue
Page 25