Piston
damage by foreign material
( Ref.: 4, 4A & 4B)
4 - piston shows imprints of small
cylindrical parts on the dome
Possible Cause
needles of broken wrist pin bearing trapped in the squish area
between the piston and head, destroy the dome, ring land and rings.
make certain to check the condition of the big end rod bearing and
cage
4a - Small ball shaped imprints on
piston dome
Possible Cause
foreign material, e.g. a pop rivet head, has entered the engine
and was trapped in the squish area, before leaving through the exhaust port. In some cases
the engine continues to run normally until the ring fails
4B - Piston shows a vertical groove
on the skirt connected to the wrist pin hole.
Possible cause:
A wrist pin circlip has come loose and was trapped in the transfer
port window.
Note always use NEW circlips when rebuilding an ultralight
aircraft engine.
4B
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