levis - The 10 Series McCulloch saws are piston ported and you will not see the piston rings when looking through the intake port, the rings are only visible through the exhaust port on the PM800 and related 10 Series McCulloch saws.
On piston ported saws, the rings are visible through the exhaust port when the piston moves down to open the exhaust:
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On the intake side, the piston skirt closes the intake port except when the piston is near TDC (Top Dead Center) when the skirt moves past the port, allowing atmospheric pressure to push the air/fuel charge into the low pressure in the crankcase. In the photo below, if you look very carefully you can see the bottom of the piston skirt and the connecting rod through the intake port.
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This You Tube video depicts a piston ported engine although I have never seen one with the exhaust and intake on the same side as they show.
Mark