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Gentlemen,
I have been building engines for a number of years and I have read about and talked to many builders over these years about piston to cylinder sealing techniques. I started building steam engines with a graphite packing in a groove in the piston, Stuart 10V, 10H etc. I then purchased a Stuart Twin Launch engine. This came with a set of iron rings. I machined my pistons for them and mounted them but this engine only ever operated on air at shows so I couldn't judge the quality of cylinder sealing. If a steam engine leaks a little past the rings it's not the same as an IC engine. My first IC engine was the Paul Briesch Little Brother hit and miss engine. His drawings called for a tight fit of the piston with I believe a couple of oil grooves on the piston. I don't have my drawings any longer so I'm going from memory. I met Paul at a show one time and talked at length about his engines and engines in general as I was just learning about IC engines. He had his engine running at the show (I presume without rings as per his design) and it ran quite well albeit kind of messy as he dripped a lot of oil into it. My Little Brother would run but not great. As I learned more I changed a few things to his original design which helped the performance but it still never ran great. Feeling that compression was part of my problem and not having any way to exactly measure the pressure I decided to make a set of rings for it. Now I had heard of other modelers using 'O' rings but was highly skeptical to use them for several reasons. First and foremost is that although 'O' rings are used for cylinder sealing devices they aren't generally used in high speed movement applications such as an engine piston running back and forth but more for a hydraulic piston sliding inside a cylinder. Second is the drag factor. If you try to measure an 'O' ring it's darn near impossible. You can turn up a bar to what is supposed to be the I.D. and keep test fitting the ring until you get what you feel is a 'good fit' (whatever that might be), measure the 'O' ring thickness and that will give you the O.D. But now the question arises, how much difference between bore and cylinder wall do you allow for the 'O' ring?, too much and you have no seal, too little and the rings drags and creates more friction than the engine can overcome so now you have another problem. At this point I'm not saying that they won't work I'm just saying that it seems very trial and error to make them work effectively. Now back to my direction. I had started purchasing Strictly I.C. magazine from early on and an article was published by the author George Trimble on making iron piston rings. I followed what was outlined in the article and made rings for my Little Brother engine. Boy oh boy what a difference in compression! I have the original set in that engine and have probably 20 hours of running time on it and the compression is still great. My compression gauge is flipping the engine up on compression and seeing how well it bounces back. Kind of a seat of the pants gauge. I have since read about other methods for making iron rings, with each author expounding on his design. I'm sure they all have their merits. I can say that I have used one other method but it seemed quite fiddly to me so I still use Trimble's method. Now if someone doesn't want to go to the effort of making iron rings and would like an alternative to 'O' rings I have another method. In the process of making my miniature spark plugs with Teflon insulators I thought about making a Teflon piston ring. This would provide simplicity of manufacture, accuracy of machining, heat environment tolerance and the anti friction quality of Teflon. Just get a piece of Teflon large enough to make your ring, drill it, bore it, turn it and cut it off. Ah but you say, how can I get it onto my piston? Take a sharp utility knife and cut it open. Personally I recommend cutting it at an angle. Have I tried it? Yes I have. Does it work? Yes it does. How do they compare to iron rings I can't honestly say. I have used them in steam engines and one I.C. engine, which I don't run a lot, but they do work, and better than 'O' rings.
Thanks for your time,
gbritnell
I have been building engines for a number of years and I have read about and talked to many builders over these years about piston to cylinder sealing techniques. I started building steam engines with a graphite packing in a groove in the piston, Stuart 10V, 10H etc. I then purchased a Stuart Twin Launch engine. This came with a set of iron rings. I machined my pistons for them and mounted them but this engine only ever operated on air at shows so I couldn't judge the quality of cylinder sealing. If a steam engine leaks a little past the rings it's not the same as an IC engine. My first IC engine was the Paul Briesch Little Brother hit and miss engine. His drawings called for a tight fit of the piston with I believe a couple of oil grooves on the piston. I don't have my drawings any longer so I'm going from memory. I met Paul at a show one time and talked at length about his engines and engines in general as I was just learning about IC engines. He had his engine running at the show (I presume without rings as per his design) and it ran quite well albeit kind of messy as he dripped a lot of oil into it. My Little Brother would run but not great. As I learned more I changed a few things to his original design which helped the performance but it still never ran great. Feeling that compression was part of my problem and not having any way to exactly measure the pressure I decided to make a set of rings for it. Now I had heard of other modelers using 'O' rings but was highly skeptical to use them for several reasons. First and foremost is that although 'O' rings are used for cylinder sealing devices they aren't generally used in high speed movement applications such as an engine piston running back and forth but more for a hydraulic piston sliding inside a cylinder. Second is the drag factor. If you try to measure an 'O' ring it's darn near impossible. You can turn up a bar to what is supposed to be the I.D. and keep test fitting the ring until you get what you feel is a 'good fit' (whatever that might be), measure the 'O' ring thickness and that will give you the O.D. But now the question arises, how much difference between bore and cylinder wall do you allow for the 'O' ring?, too much and you have no seal, too little and the rings drags and creates more friction than the engine can overcome so now you have another problem. At this point I'm not saying that they won't work I'm just saying that it seems very trial and error to make them work effectively. Now back to my direction. I had started purchasing Strictly I.C. magazine from early on and an article was published by the author George Trimble on making iron piston rings. I followed what was outlined in the article and made rings for my Little Brother engine. Boy oh boy what a difference in compression! I have the original set in that engine and have probably 20 hours of running time on it and the compression is still great. My compression gauge is flipping the engine up on compression and seeing how well it bounces back. Kind of a seat of the pants gauge. I have since read about other methods for making iron rings, with each author expounding on his design. I'm sure they all have their merits. I can say that I have used one other method but it seemed quite fiddly to me so I still use Trimble's method. Now if someone doesn't want to go to the effort of making iron rings and would like an alternative to 'O' rings I have another method. In the process of making my miniature spark plugs with Teflon insulators I thought about making a Teflon piston ring. This would provide simplicity of manufacture, accuracy of machining, heat environment tolerance and the anti friction quality of Teflon. Just get a piece of Teflon large enough to make your ring, drill it, bore it, turn it and cut it off. Ah but you say, how can I get it onto my piston? Take a sharp utility knife and cut it open. Personally I recommend cutting it at an angle. Have I tried it? Yes I have. Does it work? Yes it does. How do they compare to iron rings I can't honestly say. I have used them in steam engines and one I.C. engine, which I don't run a lot, but they do work, and better than 'O' rings.
Thanks for your time,
gbritnell
