During a recent outing, the shaft of my OS50SX sheared off in mid-flight, and my propeller and spinner disappeared into oblivion. I may have overtightened the spinner nut, or it may have been fatigue failure from too many flights at 17000 rpm on the nose of my Patriot. Why it failed is not important. I disassembled the engine and all of the internals are still in good condition. I pressed the crankshaft out of the case and bearings and can easily reinstall a new one. But before I make the decision to purchase a new crank rather than an entirely new engine, I need to know that I can safely reassemble the engine.

How does one compress the ring on the piston so that the sleeve can be re-inserted into the casing and over the piston. I haven't a clue!

It can't be too hard, as the engine was assembled in the factory. Anyone know how?

Usually there is a large chamfer on the bottom of the cyl. sleeve. If the ring is pinned, line up the ring gap with it. oil the chamfer and the sleeve. slide the sleeve down the crankcase and start the piston in. Rock the piston back and forth a bit on the rod and with a bit of pressure on the sleeve, the ring will compress. Try fitting it out of the engine with the old ring and you will see what I mean. Just takes a bit of patients and finagling. Make sure the ring stays in the groove as you start it in. If it isn't it's easy to break the ring. Hope this helps.

I just finished replacing the ring on my ST61. Don't know if this will work on the OS, but on mine, I could actually fit the piston in the liner first and then with the ring at the bottom of the liner, I could just fit the con rod on the crank. This made it easy to get the new ring in the liner first as I could easily control the piston without it being on the crank.

Like I said, worked for me, but your results may vary....

Duke