Derbi Rambla 250 Manual page 21

Characteristics
Distance "A" to be measured is a value of piston recess, it indicates by how much the piston crown
descends below the plane formed by the cylinder crown. The further the piston enters into the cylinder,
the thinner the base gasket to be used should be (to compensate the compression ratio) and vice versa.
NOTE
DISTANCE «A» SHOULD BE MEASURED WITH NO GASKET FITTED BETWEEN THE CRANK-
CASE AND THE CYLINDER AND AFTER RESETTING THE DIAL GAUGE, WITH SUPPORT, ON A
GROUND PLANE
Name
Shimming
Shimming
Shimming
Products
Product
AGIP CITY HI TEC 4T
SHIMMING FOR 250 ENGINES
Measure A
3.70 - 3.60
3.60 - 3.40
3.40 - 3.30
R
ECOMMENDED PRODUCTS TABLE
Description
Engine oil
Thickness
0.4 ± 0.05
0.6 ± 0.05
0.8 ± 0.05
Specifications
SAE 5W/40, API SL, ACEA A3, JASO MA
CHAR - 21