DS 19 OPERATION No. DS 112-3 : Overhauling a cylinder head. Op. DS 112-3 74
TOOLS
NOTE – Since the cylinder head is made of aluminium, one cannot replace the sparking plug tubes or the valve
seats without the use of special tools. Avoid removing the studs. It is however possible to replace a stripped
or damaged thread by a “HELI-COIL” thread, see note MR-4279
2 To replace the valve guides (Fixture 1644-T, see Pl. 9)
a) To withdraw the faulty guide or guides (see Pl. 8, fig.1) :
Place the screw (D) in the guide to be withdrawn by inserting it through the combustion chamber.
Place the tube (C) and the washer (B) in position and screw the nut (A) on the screw (D). Grease the thread
of the screw (D) and the faces of the washer (B) with tallow.
Hold the screw (D) and tighten the nut (A) until the guide is withdrawn.
b) To refit a new guide.
On the screw (D) fit the socket (E) (for the inlet guide, see Pl. 8, fig. 2) or the socket (G) (for the exhaust
valve guide, see Pl. 8, fig. 3).
Insert the screw (D) together with the socket (E or G) in the guide bore.
Insert the screw, socket and guide assembly through the combustion chamber and put the socket (F), the
washer (B) and the nut (A) in position. Grease the thread of the screw (D) and the faces of the washer (B)
with tallow.
Hold the screw (D) and tighten the nut (A) after making sure that the guide is correctly positioned (see l. 8,
fig. 2 and 3), the lowest part of the end of the guide must be directed towards the centre of the combustion
chamber. If necessary, make a reference mark at this point with a spot of paint before fitting the guide.
Tighten the nut (A) until the bearing face of the socket (E o G) rests on the face of the valve seat (the latter
must be clean) Fixture 1644-T
17 mm spanner
c) Reamer the new valve guides to a diameter of 9±
0.015 mm
(reamer 1642-T, see Pl. 9, fig. 2).
0.010 mm
Check the bore with a “GO-NO GO” plug gauge or failing this, with a valve stem. Too much clearance
leads to excessive oil consumption Reamer 1642-T
3 To grind the valves (valve grinder, Black and Decker type).
NOTE – The face angle of the inlet valve is 120°.
The face angle of the exhaust valve is 90°
Chamfer the corners of the valve heads to approximately 0.5 mm (at “a” and “b”, see Pl. 4, fig. 3).
4 To grind the valve seats (see Pl. 4).
NOTE – The width “l” of the seat must be between 0.9 and 1.5 mm (see fig. 3).
In order to obtain these dimensions, use the following grinding wheels :
Inlet valve seating:
For the seating 120° wheel 1662-T
For the top clearance 150° biconical wheel 1630-T
For the bottom clearance 90° biconical wheel 1630-T
To Next Page
Loading...
