Benelli ZAFFERAN 250, Service Manual

Page: 105 / 187

105
12.
Cylinder Body and Piston
Preparation documents------------12.1
Failure diagnosis--------------------12.2
Cylinder body------------------------12.3
Piston----------------------------------12.4
12.1 Preparation Documents
Function of the cylinder body: cylinder body provides space for gas compression, combustion
and expansion.
It also transfers part of its heat energy to the cooling medium inside the cylider.
Function of piston:
1. Piston bears pressure arising from mixture gas combustion cycle inside the cylinder and
transfers the pressure to the connecting rod to make the crankshaft rotate.
2. It forms the combustion cylinder along with the cylinder cap.
Notes
All parts shall be cleaned and blown by high pressure air before testing.
Preparation Standard
Item Standard value Usage limit
Cylinder
Inside Diameter
69-69.01 69.5
Cylindricity 0.005 0.05
Circular degree 0.05
Flatness 0.02 0.05
Piston
Piston
ring
Piston
pin
Piston mark direction
“IN” against the
inlet valve
/
Measuring point of piston outer
diameter
68.96-68.97
（
at
the bottom of piston
skirt
12mm
）
68.91
Piston pin housing bore Inside
Diameter 17.002-
17.008 17.04
Outer diameter of piston pin
16.992-17 16.96
Clearance between cylinder and
piston 0.035-0.045 0.10
Clearance
between
piston
ring and ring
groove
first ring 0.015-0.05 0.08
second ring 0.015-0.05 0.08
Clearance of the
closed mouth of
piston ring
first ring 0.35-0.55 0.70
second ring 0.35-0.55 0.70
Oil ring 0.2-0.7 /
Clearance between piston and piston
pin 0.002-0.016 0.02
ID of wrist-pin end of connecting rod 17.010-
17.018 17.06
Clearance between connecting rod
and piston pin
unit: mm
0.010-0.026 0.06