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A new attempt at making piston rings

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  • Jerry---I've answered your posts a couple of times and called you Mike.--Sorry about that. senility setting in--Brian
    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • Originally posted by J Tiers View Post
      That accounts for the insistence on clamping the rings flat in the heating fixture. If not flat, they won't seal well against the groove.
      I would think that surface grinding them flat after heat treating would be the way to go. I seem to recall that the Chevy 350 only had around 4 or 5 pounds of ring pressure against the cylinder walls due to "spring" from the rings -- the rest of the sealing pressure came from the gasses themselves. Which means that the ring grooves need to be extremely parallel and straight and flat, etc.
      25 miles north of Buffalo NY, USA

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      • someone above mentioned a fixture for lapping rings to get the ODs perfectly round. Given all your experience with lapping pistons in, trying that might be worth a shot.

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        • Brian, I have no experience with model engines or making rings, but have been around the hot rodding world for a long time, as have you. One trick the rodders use is to drill gas passages into the top of the piston that intersect with the bottom of the ring groove. This lets the combustion gas pressure get behind the ring easier and force the ring into the cylinder wall. Just a suggestion, thinking outside the box.

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          • bluechips---Thank you. I too have spent a lifetime around hotrods, and I did know about that trick. It's pretty extreme stuff though.---Brian
            Brian Rupnow
            Design engineer
            Barrie, Ontario, Canada

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            • Hi Brian,
              A long while ago I made a 15cc petrol engine of my own design, which (by luck) worked very well. I recall making the piston rings by machining a tube of cast iron oversize enough. I then cut a slit about 1/8" wide the whole length of the tube. Then I put it in the 3 jaw chuck and tightened the jaws so that it closed the slit. With the gap closed by the chuck jaws I machined the rings to the desired size and parted them off. I think I lapped the rings down to the required thickness afterwards, They seemed to work well. You may have considered doing this already but I just thought I would mention it anyway. Good luck and keep up the good work.

              Alan

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              • Aren't we all happy we are not trying to seal a Wankel / rotary piston engine? Apex/ side etc.

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                • Any update?

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                  • Yes Ringo.--I have bought a toolpost Grinder for my lathe and I'm in the middle of buying a heat treat oven. As soon as I have both items I will carry on with my ring making exercise.---Brian
                    Brian Rupnow
                    Design engineer
                    Barrie, Ontario, Canada

                    Comment


                    • Just another design suggestion that helps break in seating. Angle the face slightly to provide point contact with the bore.

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                      • There is no joy in Mudville today. I put a new piston and two rings I had purchased from Debolt in the newest vertical i.c. engine-2021 and had no compression. I squirted some oil down the sparkplug hole and had lots of compression. The new rings are not sealing. I drove the engine for 2 hours with an electric motor, hoping that the rings would "bed in" and seal, but it's not happening.----So---I have one trick left. That is to build a fixture as per Mr. Chaddock, and turn the o.d. of the rings to be perfectly cylindrical. That is exactly why I bought the toolpost grinder. I doubt my ability to take a 0.0005" depth of cut with a lathe tool, but with the grinder it may be possible.
                        Brian Rupnow
                        Design engineer
                        Barrie, Ontario, Canada

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                        • Here we have Mr. Chaddocks fixture for turning the outer diameter of piston rings to make them truly round. The sleeve in my hand has an internal bore of 1.00". The rings are sprung into the sleeve, the sleeve with rings in it slides over the part held in the chuck, then the washer on the very end is tightened down with the bolt, which squeezes all of the rings together. The o.d. of the 1/4" thick washer is slightly smaller than 1", so after the bolt is snugged up tight, the sleeve is slid off over the washer, leaving the rings ready to be turned or ground to a perfect diameter. I am going to use my toolpost grinder to do that.


                          Brian Rupnow
                          Design engineer
                          Barrie, Ontario, Canada

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                          • Brian, are you familiar with the ancient Brit-Iron approach to bedding rings? (When the engine is running puff some Comet or BonAmi cleanser into the carb intake.)

                            -js
                            There are no stupid questions. But there are lots of stupid answers. This is the internet.

                            Location: SF Bay Area

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                            • Jim---yes---I am. The key to that is "When the engine is running!!"
                              Brian Rupnow
                              Design engineer
                              Barrie, Ontario, Canada

                              Comment


                              • I begin to wonder if the bore doesn't have something to do with it. That's an awful large number of failed attempts. Has the bore been checked for roundness? I am not very fond of the "look for light" method. The spring-hone you mentioned trying really isn't what I'd like to see used in this case - a rigid hone is what you want.
                                Last edited by eKretz; 05-10-2021, 08:54 PM.

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