Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

That is a fine looking steam plant.

Seems you may be correct, that it is whatever the piston rings turn out to be, expanding and binding as they heat up when running.

I think you'll have to do a bit more than just pull the cylinder head to see the piston rings, as the piston needs to move beyond its TDC position and start out of the cylinder end to address the rings.

Good luck, and I hope it proves to be a simple fix!

You can leave the head on and pull the cylinder. You will probably find the builder either used an aluminum piston, teflon rings or orings that are not a proper fit. The ring grooves have to be cut to a different formula for orings than cast iron or teflon rings. I recommend going to the local plumbing supply house and buying some teflon packing yarn or better yet, graphite packing yarn. Cut a length to fit in the ring groove (one is sufficient-you don't need 3). let the yarn stick out just a little more than being flush with the inside diameter of the cylinder, then force the piston back into the cylinder. Any excess yarn should be shaved off by the sharp front edge of the cylinder, and you will have a perfect fit. This method was used in real steam engines long before rings, but needed changed more often . Since i don't run my model engines24/7 the graphite yarn never wears out and break in time is immediate.
Of course, if your cylinder is scored badly or elliptical in shape, you will have some machining to do.
Show us some pictures when you get it apart.
crazydoug

If you can't find graphite yarn, i can mail you a piece.