Pinned rings....or not

[gabriel]

My only real experience with the deep insides of a 2 stroke come from dirt bikes when I was younger.

One thing I noticed on this 707D that is VERY different than my old RM250 (that I rebuilt probably a dozen times) is the rings are not pinned.  There's no pin the ring groove to keep them from rotating. 

It was always my understanding when fooling with dirt bikes that the ring gap should NEVER pass a port and that was the reason for the pins.

Anyone have some insight into this or do I just need to reassemble and stop worrying about cråp that don't matter?


Thank you.

[sweepleader]

If I felt confident that the piston was OEM, I would not be concerned about it. The Homelites that I have had apart had pins in them. A knockoff piston might be missing the pin for economy's sake, that would worry me. Check the service manual, there might be something there. Others here will hopefully have some insight to share.

[sawnami]

I know that Power Products AH-80 (131cc) engines didn't have locating pins because the exhaust port was bridged to keep the ring from coming out into the port. They had a performance version cylinder without the bridge in the exhaust port and the piston was pinned to keep the ring gaps from rotating into the wide open exhaust port.
If there isn't a locating pin, I would say that there isn't a risk of the ring end expanding into the port. I've put together several makes and models of saws without pinned pistons without any problems.

[onlyhomelites]

I'm thinking Dan could be right about an aftermarket piston...here's an old pic of a NOS piston I had at one time and it clearly shoes the pin driven in from the top.