1 crucial point, make sure your circlips have gap on top or bottom, never on side, they can compress and pop out.
That is refering to TOP of piston, or BOTTOM of piston? Aka towards crank or sparkplug?
You want to make sure to position them with the openings pointing owards the top or bottom of the piston, ie, towards the head/sparkplug or the crank shaft, in the direction of movement. otherwise they can compress and pop out.