I am not new to RC hobby, however, most of my engines have been
ABC type (without rings). I have to install a new piston ring in a 50
OS engine. I am afraid to broke the ring trying to install it. Can someone
give me a hint in doing it properly ?

Enrique:

With the cylinder head off, before doing any further disassembly, make sure the top of the cylinder bore is perfectly clean. Scrub it with steel wool and a light oil to be sure.

Put the new ring in the bore above the piston, then turn the crank to get the ring absolutelty straight, and bring the ring up to the top of the cylinder. Turn the crank back to move the piston down, then use a 0.003" feeler to check the ring gap. Three thousandths of an inch is ballpark for a 0.40-0.60 engine. If it's more, ask the ring supplier what he recommends, and if necessary, send the ring back for exchange.

Take the piston out, lightly clamp the con rod in a vise to hold the piston. It's practice time. Hook both thumbnails in the gap of the ring, and using your index fingers to control the ring, pull your thumbs apart to open the ring, and lift it off the piston. Put it back on and take it off a few times until you can do it freely. You are practicing with the old ring, if you slip and break it, well you are planning to throw it away anyhow.

When you've learned to handle the ring, leave it off, take the piston and rod out of the vice and clean them thoroughly. The antifreeze and crock pot method works fine.

Wrap some 600 grit wet-or-dry paper around your finger, and with some more light oil scrub the cylinder bore. You want to scuff it lightly, but not take any metal out.

If you want to replace the bearings, do it now.

With everything clean inspect the ring groove in the piston - make sure there is no black staining in the bottom of the groove, and check to see if there is a locating pin that goes in the ring gap. You wont find a pin on a four stroke engine, and not all two strokes have them either.

If there is no locating pin after putting the ring on the piston set the ring in the sleeve with the gap aligned with a place on the sleeve between the bypass and exhaust ports, where the gap will not cross any open areas of the sleeve. If it's pinned, then it is automatically located.

Put the engine back together, oiling it liberally, mount it on a stand and run it in.

Fly it asnd enjoy.

Bill.

Hello!
putting on a ring is easy!
Just take apart the engine so you have the piston in your hand. Check the pistonring slot in the piston so no dirt is visible .....Then!
Take the new pistonring
and lay it on top of the the piston. Then press the ring apart somewhat so you could push the ring over the the piston on just one side.....just a little.......Do this carefully! Then carefully widen the ring somewhat more and push it over the piston so that it seats in the slot in the piston.
That's it!
This is more easily done in practice than it is to write about........

Regards!
Jan K
Sweden

Don't try to spread it far enough to go over the piston all at once. Spiral it on- that is, put one end into the ring land and roll it around. This way requires a lot less pulling on it, and warping.

Hi!
correct!

Regards!
Jan K