Husqvarna 545RXT AT Workshop Manual page 64

14.5.5 Piston ring guide pin vibrated loose
A too high engine speed can cause the ends of the piston
ring to hammer against the guide pin when the piston
ring moves in its groove. The intensive hammering can
drive out the pin through the top of the piston causing
serious damage also to the cylinder.
64 – English
The guide pin for the piston ring has been pushed up
through the top of piston.
Cylinder and piston