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A new attempt at making piston rings

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  • Originally posted by brian Rupnow View Post
    Every time I use a T handle tool like that, it scares me right to death. [snip]
    If I were doing it, I would put the lathe in high "gear" & turn the VFD way down so there would be very little torque available. I.e., a grab would stall the motor. Now, if you don't have a VFD, here's another good reason to get one.

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    • The news is positive. With new cast iron cylinder, piston, and rings, the engine has high (to coin a new word) Suckability!!! It fired, it ran for three short blasts, but I'm having head gasket issues. The aluminum head has a ring of material that fits down into the top of the cylinder about 0.060". Or, let me rephrase that--It is supposed to extend down into the cylinder about 0.060" minus the 0.030" thickness of the head gasket. A close examination of the cylinder head shows that that ring of material is "hanging up" on the inside of the bore and not letting the head bolts tighten the cylinder down evenly all the way around. I'm going to set the cylinder head up on the lathe and trim a tiny bit off that diameter that is giving me problems.
      Brian Rupnow
      Design engineer
      Barrie, Ontario, Canada

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      • It proves that lapped pistons into their cylinder seal well. The rings are just along for the ride and are not the primary seal. If you want to try something for fun, remove the rings and try it again, it likely will run the same.

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        • Sparky--I'm afraid that you are probably right. Every time you take these little rings off a piston they lose their proper shape a little more. I've had this little engine apart and back together so many times now that I can do it with my eyes closed. All of this is being done in a quest to better understand how to make my own cast iron rings and run them instead of a Viton o-ring. I'm getting filled up with ring theory, but I'm not having a lot of success on the practical end of things.
          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

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          • I am going to bring up the George Trimble method again. As you know, many many people have made rings using that method and had great success, in fact I have not seen a report yet of the method NOT producing a good working set of rings. I am sure you seen all the posts from people making good rings with the method, often on their first and only try. Why you are avoiding that method and trying every other possible method is beyond me. If you follow the George Trimble method exactly with good machining practices you are almost guaranteed a good working set of rings. I stress following the method exactly including the fixture, close does not count.

            I know you have books and articles by other engine builders on their methods BUT from what I read the George Trimble method is considered the best AND most often used for that reason.

            Or..... stay at it in hopes of developing the Rupnow method.
            Last edited by Sparky_NY; 05-29-2021, 06:09 PM.

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            • Sparky--I thought you were going to send me the article on the Trimble method. Keep in mind--the rings that are on the piston are the rings I purchased out of USA from Debolt. The first rings I made were not suitable and were never used on a running engine.
              Last edited by brian Rupnow; 05-29-2021, 06:56 PM.
              Brian Rupnow
              Design engineer
              Barrie, Ontario, Canada

              Comment


              • Originally posted by brian Rupnow View Post
                Sparky--I thought you were going to send me the article on the Trimble method. Keep in mind--the rings that are on the piston are the rings I purchased out of USA from Debolt. The first rings I made were not suitable and were never used on a running engine.
                This link might work for you,

                https://r.search.yahoo.com/_ylt=Awr9...tkAZh21AAJ4T0-

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                • Originally posted by doctor demo View Post
                  I'd always thought what the writer in the link calls the cold forming method made sense. From scanning decades of Model Engineers my impression is its "the", or perhaps "a", standard method. What's it lack that cause people to pursue the heat treat methods?
                  in Toronto Ontario - where are you?

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                  • I'm having a no work Sunday---I need it. But the old brain cells keep clicking away. Every thing I read about rings recommends that the ring thickness should be 1/30 to 1/25 of the cylinder bore (and the depth of the ring can match the width so your ring actually has a square cross section). On a 1" bore, that gives a ring width of 0.033" to 0.040". The width of the groove in the piston should be 0.001" greater than the width of the ring itself. So---If I made my rings 0.038" wide, then the groove in the piston should be 0.039"---And 1 millimeter is .0394". Okay, cool!!! Now, where do I buy a 1 mm wide grooving tool? I have googled this and still have no clear answer. I can turn a lathe tool for general purpose turning from HSS, but I don't trust myself to be able to make a 1 mm wide grooving tool. I don't want to spend a zillion bucks on this either. My lathe has a 12" swing, and it has a quick change toolpost on it. I prefer 3/8" square tooling, but in a pinch I can mount 1/2" square tooling. I'm not averse to using inserted carbide if the price for the carbide and the appropriate holder don't break the bank. Since the piston groove will be in cast iron or aluminum, I could even work with 1mm wide HSS and a 3/8" square shank.---Thanks.---Brian
                    Brian Rupnow
                    Design engineer
                    Barrie, Ontario, Canada

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                    • Although I realize that having the sides of the grooving tool exactly parallel to each other is paramount I don't see that much of an issue grinding the tool from a HSS blank.
                      The one pictured below is made using a 3/16" blank. It is .025" at the tip and is used for snap ring grooves.

                      Home, down in the valley behind the Red Angus
                      Bad Decisions Make Good Stories​

                      Location: British Columbia

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                      • That looks good Willy.---I never even thought about grinding one from a smaller piece of HSS.
                        Brian Rupnow
                        Design engineer
                        Barrie, Ontario, Canada

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                        • narrow grind a cut off bit??

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                          • Ringo--I have to think on this a bit. I have two or three different grinders here, but other than the toolpost grinder, none of the other grinders are used in any kind of precision grinding. I would have to create a fixture which gave me very precise control over the depth of material I was grinding away, and by the time I have done that it would be much simpler if I bought a pre-ground tool of the correct width and parallelism.
                            Brian Rupnow
                            Design engineer
                            Barrie, Ontario, Canada

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                            • If you don’t feel comfortable grinding your own, look into
                              Thin Bits.

                              Sid

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                              • Brian, I would try using a 1mm thick cutoff wheel. The inside corners of the ring groove don't have to be perfectly square if the ring never contacts there anyway. It *should* only contact on the top and bottom flanks of the groove. But if it bugs you, you could use a diamond whet stone to give it a square edge prior to grinding a groove. I would at least experiment on a piece of scrap and then look closely with a strong magnifier loupe.
                                25 miles north of Buffalo NY, USA

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