MOTORPARTS 9936650 Instrucciones De Montaje página 18

– Loosen the four M8 nuts (Fig. 5) by ½ turn each, then remove
them.
– Remove head and cylinder from the crankcase.
– Remove the piston circlip, pull out the gudgeon pin and take off
the piston from the connecting rod.
– Use a clean rag to protect the crankcase against dirt and foreign
material.
INSTALLATION
Carefully clean the cylinder mating surface on the crankcase from
any residue of the previous sealing paste.Clean and degrease the
TOP cylinder and check that the cylinder neck enters smoothly in
the casings hole by inserting it fully home. If there are hard spots, it
is recommended to remove them by ensuring that no shaving enters
in the crankcase.
• Head preparation
– Remove the carbon deposits and the sealing paste residues
from the head surface and from the combustion chamber.
– Carry out a valve seal test by pouring clean solvent in the inlet
and exhaust ducts, and check if there is any leak.
If there is a fl uid leak between valves and valve seats you have
to remove the valves and check the clearance between stems
and guides or ensure that the valves are not bent or worn.
Replace the unsuitable parts and remove the carbon deposits,
then proceed lapping the valves with the special abrasive paste.
Carefully clean the head and all parts, reassemble them and
carry out again the valve seal test.
Should it be necessary, the head lapping must be done by a qualifi ed
workshop. Otherwise place a damp sheet of glass paper (1000 grain)
on a surface plate and lap the head by moving it like an eight.
• Piston rings assembly
– Carefully clean the new piston, the piston rings and the gudgeon
pin circlips.
– Assemble one of the two gudgeon pin circlips on the piston, pay
attention not to stretch it, and check that it is placed correctly in
its seat.
– Fit the scraper ring expander in the special piston groove, then
complete the scraper ring assembly by fi tting fi rst the lower and
18