Derbi Rambla 250 Manual page 119

Engine
- Measure the diameter of the valve stem at the
three positions indicated in the diagram.
- Calculate the clearance between the valve and
its guide.
- Check that there are no signs of wear on the fay-
ing surface with the set screw articulated terminal.
- If no anomalies are found during the above
checks, the same valves can be reused. For better
sealing results, it is advisable to grind the valves.
Grind the valves gently with fine-grained lapping
compound. Upon grinding, keep the cylinder head
in horizontal position. This will prevent the lapping
compound residues from penetrating between the
valve stem and the guide (see figure).
CAUTION
TO AVOID SCORING THE FAYING SURFACE, DO NOT RO-
TATE THE VALVE WHEN NO LAPPING COMPOUND IS
LEFT. CAREFULLY WASH THE CYLINDER HEAD AND THE
VALVES WITH A SUITABLE PRODUCT FOR THE TYPE OF
LAPPING COMPOUND BEING USED.
NOTE
DO NOT CHANGE THE VALVE FITTING POSITION
Characteristic
Valve check: standard length
Outlet: 94.4 mm
Valve check: standard length
Inlet: 94.6 mm
Valve check: maximum clearance allowed:
Outlet: 0.072 mm
Valve check: maximum clearance allowed
Inlet: 0.062 mm
Valve check: standard clearance:
Outlet: 0.025 ÷ 0.052 mm
Valve check: standard clearance:
Inlet: 0.013 ÷ 0.040 mm
Valve check: Minimum diameter admitted:
Outlet: 4.95 mm
Valve check: Minimum diameter admitted:
Inlet: 4.96 mm
Valve check: Standard diameter:
Inlet: 4.972 ÷ 4.987 mm
ENG - 119