Hello Rob,
What steam pressure are you operating at?
Do you have an estimate of the superheat?
I agree with Tom G that cast iron rings on cast iron cylinders is the traditional method.
In today's world, other metals like steel or brass might also be possible.
Teflon might be an option if the pressure and temp are not too high.
My experience with Teflon O rings in hot oil piping flanges is that 500 F is the upper limit. This was with the O rings captive in grooves. In a sliding seal situation, the limit is probably lower. One issue is that Teflon starts to distort around 500F. When you remove the seal after exposure to high temp, you probably will not be able to re-install the seal.
Not sure where one would find the proper size CI rings except to make them.
I am told that back in the 1920's mechanical engineering students were required to take fairly extensive machine shop classes.
At the U of Minnesota, one of the projects they did was to fabricate new piston rings for a Ford Model T engine using cast iron sewer pipe as the source material.
I dunno - could work, but I am not sure how one would go about it.
If you run iron on iron, you will need cylinder lubrication. Maybe you already have this. Cast iron is usually porous enough (due to the carbon flakes) that it holds oil well and does a good job of polishing itself when running against an iron cylinder. For a small model engine, a "pressure pot" feeder on the steam line, holding a few drops of oil, is probably enough. You have to periodically refresh the oil charge because under the heat of the steam, the oil is slowly emulsified and carried away with the exhaust steam.
Another item that you probably know: Traditional steam engine design has a slight relief in the cylinder bore at top and bottom center. The relief only needs to be 0.010" or so on the radius. The idea is that the outer ring slightly overruns the relief with each stroke, and thereby does not generate a ridge on the cylinder. The usual overrun of the ring is about 20% of the ring width. Without the relief, steam engines can really get to pound as wear accumulates in the crank and cross-head bearings. (I guess the Teflon rings would not need a relief). If you decide to install CI rings (or other metal rings), you might want to think about boring in a relief at each end of the cylinder.
Post some pics if you get a chance.
I would be interested to see the engine.
Regards,
Terry S.
You can find more information on our web, so please take a look.
Just wornding what piston ring material would be best for me the engine is a gen iv bbc with a 4.530 bore and dart iron eagle heads. Most cylinders are and pretty good shape but a few have minor scuffs and I don't have the tools for measuring out of round nit going to a machine shop as where I live in canada they are way over priced as there's very few so I ordered cast rings because of this but they accidentally sent moly ones and I heard u want a 100% perfect finish for moly rings am I best to send em back and get cast? That and I already Honed it at 220 or 240 grit
These are the rings they sent me
Piston Rings, Premium Ductile Ring Sets, Plasma-moly, 1/16 in., 1/16 in., 3/16 in. Thickness, 8-cylinder, Set of 8
If you want to learn more, please visit our website Dongya.
Last edited by 502nova3; 06-11-2023 at
04:10 PM
.Hello Rob,
What steam pressure are you operating at?
Do you have an estimate of the superheat?
I agree with Tom G that cast iron rings on cast iron cylinders is the traditional method.
In today's world, other metals like steel or brass might also be possible.
Teflon might be an option if the pressure and temp are not too high.
My experience with Teflon O rings in hot oil piping flanges is that 500 F is the upper limit. This was with the O rings captive in grooves. In a sliding seal situation, the limit is probably lower. One issue is that Teflon starts to distort around 500F. When you remove the seal after exposure to high temp, you probably will not be able to re-install the seal.
Not sure where one would find the proper size CI rings except to make them.
I am told that back in the 1920's mechanical engineering students were required to take fairly extensive machine shop classes.
At the U of Minnesota, one of the projects they did was to fabricate new piston rings for a Ford Model T engine using cast iron sewer pipe as the source material.
I dunno - could work, but I am not sure how one would go about it.
If you run iron on iron, you will need cylinder lubrication. Maybe you already have this. Cast iron is usually porous enough (due to the carbon flakes) that it holds oil well and does a good job of polishing itself when running against an iron cylinder. For a small model engine, a "pressure pot" feeder on the steam line, holding a few drops of oil, is probably enough. You have to periodically refresh the oil charge because under the heat of the steam, the oil is slowly emulsified and carried away with the exhaust steam.
Another item that you probably know: Traditional steam engine design has a slight relief in the cylinder bore at top and bottom center. The relief only needs to be 0.010" or so on the radius. The idea is that the outer ring slightly overruns the relief with each stroke, and thereby does not generate a ridge on the cylinder. The usual overrun of the ring is about 20% of the ring width. Without the relief, steam engines can really get to pound as wear accumulates in the crank and cross-head bearings. (I guess the Teflon rings would not need a relief). If you decide to install CI rings (or other metal rings), you might want to think about boring in a relief at each end of the cylinder.
Post some pics if you get a chance.
I would be interested to see the engine.
Regards,
Terry S.
Just wornding what piston ring material would be best for me the engine is a gen iv bbc with a 4.530 bore and dart iron eagle heads. Most cylinders are and pretty good shape but a few have minor scuffs and I don't have the tools for measuring out of round nit going to a machine shop as where I live in canada they are way over priced as there's very few so I ordered cast rings because of this but they accidentally sent moly ones and I heard u want a 100% perfect finish for moly rings am I best to send em back and get cast? That and I already Honed it at 220 or 240 grit
These are the rings they sent me
Piston Rings, Premium Ductile Ring Sets, Plasma-moly, 1/16 in., 1/16 in., 3/16 in. Thickness, 8-cylinder, Set of 8
Last edited by 502nova3; 06-11-2023 at
04:10 PM
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