Derbi boulevard 125 4t Workshop Manual page 110

Engine
- Calculate the piston pin coupling clearance.
N.B.
THE PIN HOUSINGS HAVE 2 LUBRICATION
CHANNELS. FOR THIS REASON MEASURE-
MENT OF THE DIAMETER MUST BE CARRIED
OUT ACCORDING TO THE AXIS OF THE PIS-
TON.
Characteristic
Piston pin bore - standard diameter
Ø 15+0.001 +0.006
- Measure the outside diameter of the piston, per-
pendicular to the gudgeon pin axis.
- Measure 36.5 mm from the piston crown's shown
in the figure.
N.B.
THE PIN HOUSINGS HAVE 2 LUBRICATION
CHANNELS. FOR THIS REASON MEASURE-
MENT OF THE DIAMETER MUST BE CARRIED
OUT ACCORDING TO THE AXIS OF THE PIS-
TON.
- Using a bore meter, measure the inner cylinder
diameter at three different points according to the
directions shown in the figure.
- Check that the coupling surface with the head is
not worn or misshapen.
- Pistons and cylinders are classified into catego-
ries based on their diameter. The coupling is car-
ried out in pairs (A-A, B-B, C-C, D-D).
Characteristic
Maximum allowable run-out:
0.05 mm
- The cylinder rectifying operation should be car-
ried out with a surfacing that respects the original
angle.
- The cylinder surface roughness should be 0.9
micron.
- This is indispensable for a good seating of the
sealing rings, which in turn minimises oil consump-
tion and guarantees optimum performance.
ENG - 110