I disassembled my OS 95AX to examine the internals. Everything looks okay. I was wondering about the piston ring and groove. If I slide the ring along its groove I come across what looks like a small set screw (or something - its so small) inside of the piston groove. What is the purpose of this? Is it supposed to hold the ring in place? When I compress the ring the split in the ring grips this "thing" in the groove. Should I reassemble the engine so that the split part of the ring aligns with this thing in the groove? The diagram in the OS manual seems to show something is there in the groove.

Thanks.

I think that pin is supposed to go in the groove to keep the ring from rotating.

In a 2-stroke engine, a pin is used to locate the ring gap so to prevent the ends of thetrings from encountering the ports in the cylinder wall.

That would be very bad.

I put it back together. I hope I got the ring in correctly. It is impossible to slip the connecting rod onto the crank shaft with the liner totally inserted in the sleeve. I had to slip the piston into the bottom of the liner just enough to compress the ring. Then I dropped the liner and partially inserted piston into the sleeveso I could slip the rod over the crank arm.

I will start it up tomorrow and see if it self destructs or not. []

most OS's that I have run across have a taper on the bottom oof the sleeve so that it compresses the ring has you push the sleeve down over the piston. After installing the crank, I put the piston and rod in, and then rotate it so the piston is at TDC. Usually you can see to make sure the ring is lined up with the anti-rotation pin. Once you are sure, begin wiggling the sleeve down over the piston and ring. I lube it up pretty good before I start all of this. With a new ring, it is all most impossible to get the sleeve over the piston if the ring is not lined up on the pin properly.

Here's a tip that came in the instruction leaflet for my new Enya 61 ringed engine. First insert the piston into the bottom of the liner so the ring has just barely been compressed. This allows for a lot of sideways movement (wobble) of the piston and rod. Then fit the liner down into the crankcase until the rod can slip onto the crankpin then slide the liner the rest of the way down over the piston. Enya obviously understand that guys will always strip an engine and they even give instructions on a tightening sequence for the head.

ATF works very well for an assembly lube but yes, the gap in the ring must be on the index or anti-rotation pin. Use the taper at the bottom of the sleeve, put the piston in such that its tilted a little and start compressing the ring 180 degrees from the gap and slowly insert the piston so your compressing the ring towards the gap. The ring gap should be the last thing that disappears.

Hope that makes sense in writing without pictures or video

Can't imagine a situation where one could get the ring and piston to fit without the ring gap lined up with pin and not breaking something. Having to use "mongo" force to reassemble an engine usally indicates that you are doing something wrong.

A post on another forum (I kid you not)

"I used a hammer to get the piston in and now my motor is locked up...."

Warranty issue I guess.

Thanks for the tips everyone. I think Downunder explained it well - that is how I reassembled my engine.

With regards to the alignment pin (nside the groove) and ring split being aligned or else you wont get the piston in the liner - I don't think that was the case with my engine. The pin in the groove was really small and maybe my ring had a little wear. I was really worried that maybe the ring had become misalligned with the pin (since you can't see it after the piston is in the liner). But I have fired up the engine after reassembly and it did not self destruct! I wonder how long it would take the ring to rotate though during a run, though.

The purpose of the pin in the groove IS TO PREVENT the ring from rotating in the groove and possibly catching/snagging a port. If it's running good than you should be OK and the ring is in proper alignment with the pin. I believe that OS engines have a smaller"sweetspot" where everything needs to be so all the pieces can slip into place, somedays you wish you had three hands.