Derbi GPR 125 Racing, Workshop Manual

Page: 108 / 247

4 - ENGINE
108
IF THE VALVES HAVE BEEN
GROUND, WHEN THE CYLINDER
HEAD IS REFITTED ONTO THE
ENGINE, ADJUST THE VALVE SET-
TINGS.
CULATA
1. Eliminate:
- Carbon sediments (from the combustion chamber)
Use a rounded spatula.
AVOID USING ANY SHARP EDGED
INSTRUMENT THAT CAN CAUSE
DAMAGE AND SCRATCHING.
- IN THE SPARK PLUG THREADS
- ON THE VALVE SEATS.
2. Inspect:
- Cylinder head
Wear/damage => Renew .
Steps for measuring distortion and for rectification:
Place a ruler (1) and a thickness calliper (2) on the head
cylinder surface, as in the figure to the side.
CYLINDER HEAD WARP: 0.05 MM.
Incorrect warp => Rectificate .
- Lay a 400 – 600 file on a flat (and skimmed) surface and skim
the cylinder head surface by filing with a figure eight move-
ment.
TURN THE CYLINDER HEAD SE-
VERAL TIMES TO PREVENT TOO
MUCH MATERIAL BEING TAKEN
FROM A SINGLE SIDE.
SKIMMING AND PLANING A
CYLINDER HEAD REQUIRES EX-
PERT HANDS.
IF YOU DO NOT CONSIDER YOUR-
SELF AN EXPERT, IT IS RECOM-
MENDED TO LEAVE THE TASK TO
A HEAD-SKIMMING WORKSHOP.
CAUTION
CAUTION
N.B.
N.B.