Derbi boulevard 125 4t, Workshop Manual, Page: 111 / 182

- The pistons are oversized due to cylinder rectifi-
cation and are subdivided into three categories
1st, 2nd, 3rd with 0.2-0.4-0.6 mm oversize. They
are also classified into 4 categories A-A, B-B, C-
C, D-D.
Inspecting the piston
- Carefully clean the seal housings.
- Measure the coupling clearance between the seal rings and the grooves using suitable sensors, as
shown in the diagram.
- If the clearance is greater than that indicated in the table, replace the piston.
STANDARD COUPLING CLEARANCE
Name Description Dimensions Initials Quantity
Top piston ring 0.025 ÷ 0.070
Middle piston ring 0.015 ÷ 0.060
oil scraper 0.015 ÷ 0.060
MAXIMUM ADMITTED CLEARANCE AFTER USE
Name Description Dimensions Initials Quantity
Top piston ring 0.080 mm
Middle piston ring 0.070 mm
oil scraper 0.070 mm
Removing the piston
- Install piston and wrist pin onto the connecting
rod, aligning the piston arrow the arrow facing to-
wards the exhaust.
- Fit the pin stop ring onto the appropriate tool.
Specific tooling
020430Y Pin lock fitting tool
Engine
ENG - 111