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Old 04-13-2009, 10:19 PM
Steven Harrod Steven Harrod is offline
Join Date: Feb 2009
Posts: 37
Default Evaluation of Ring Condition


My initial response to the photos is that the rings are suspect. The gaps seem very large, but otherwise a photo is not an adequate judge. Rings should have a very close fit in the slot, but move freely. When the ring is compressed in the cylinder bore, the gap should measure 0.002 inch. Essentially, as close as possible without touching. The wall pressure on the compressed ring should be about 5 psi, which is much less that the typical 40 psi for IC engines, but should still require about 20-30 pounds of compression force by you to get the ring into the bore. Sounds like the rings are too light a fit by your description. My dimensions are taken from "So You Want to Build a Live Steam Locomotive"

Note, copper would be a horrible ring material. I suspect they are really bronze? Bronze is also a poor wearing ring material. The standard would be cast iron, because it is a good bearing material in contact with a cast iron cylinder, and its porous nature absorbs oil and reduces friction. Of course, it can rust, so winter layup should include a liberal dose of oil just before shutdown and blowing out with compressed air.

The real test is how much compression you achieve in the cylinder volume. Assuming the piston is detached from the crosshead, push the piston into the bore, and then push on it with a wooden board. Do you feel any resistance? Do you hear any air leaks? Get really fancy and measure the psi with a gauge. How long will it hold before bleeding off?
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