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Coltri MCH5 Redeisgned Head Piston

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  • Coltri MCH5 Redeisgned Head Piston

    Does anyone know where I can find just the piston for the 3rd stage red redesigned head. It is part number 2.2 of the attached document. Coltri sent me the kit but sent the wrong (old Style) piston. I have everything else including rings. Just need the piston. Thanks 151126-1543-new-kit-head-3rd-stage-mch-811131618.pdf

  • #2
    Why not just contact them again and ask them to replace with the right one? Unfortunately, the US distribution requires purchasing the piston and cylinder as a kit.
    Ray Contreras
    CompressorStuff.com

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    • #3
      You are correct, Ray. I am dealing with Coltri now. Looks like they recognized the error of sending the wrong piston and will be sending the correct one at no cost.

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      • #4
        Coltri seem to be having issues with supply of the third stage, or more correctly getting all the correct parts together in one assembly. I too had a new type "red head" piston/barrel assy. come with the old style piston. , I didn't notice at first, er... it works like that. Coltri sent me another. Also had problems with the valve machining not being on the same 'plane' (see http://www.cngchat.com/forum/forum/g...d-stage-valves) and again Coltri came good.

        BTW: A little birdie has given me word that those third stage barrels are 'soft as a babies bum'. Can't truly blame Coltri too much. After all, business is business and all that.

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        • #5
          FYI...according to Craig at Nuvair, they are no longer using the final stage piston (red head) with the "nipple" attached to the top of piston. It's because there were complaints of the nipple getting stuck. If air pressure is what is engaging the star plate (valve) what was the purpose of the nipple?

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          • #6
            Originally posted by cngtennessee View Post
            FYI...according to Craig at Nuvair, they are no longer using the final stage piston (red head) with the "nipple" attached to the top of piston. It's because there were complaints of the nipple getting stuck. If air pressure is what is engaging the star plate (valve) what was the purpose of the nipple?
            The nipple on the old style piston has nothing to do with opening the valve. I replaced mine with the newer flat top piston and it performs just as well. If you take your old nipple piston/sleeve and an old valve and hold them together, it is plain to see that there is plenty of clearance (the better part of a hundred-thousandths of an inch) between the tip of the nipple and the valve. In other words, there is no way that the tip of the nipple was opening the valve. I think that the crazy Italian engineers falsely believed that the nipple would increase the compression, similar to what a dome piston in an engine does compared to a dish or flat top piston.
            Last edited by hypermilinggx; 03-26-2020, 01:51 AM.

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            • #7

              Not sure what the nipple could get stuck on? If it hits the cylinder head, I'm sure you'll hear it.
              I'm struggling to see anything 'crazy and Italian' about the 'nipple' atop the piston-crown, but I'm willing to be told otherwise. It certainly doesn't open the valve.
              Without the 'nipple', the new head-design lowers the compression-ratio. All the raised crown does is replace some of the material in the compression-space created by the new valve. It reinstates the compression ratio to that of the prior design. Of course it'll work without the nipple/raised crown, I ran mine without. But there's a loss in efficiency, and because less of the now hot gas, is ejected without the 'nipple' we see hotter running.
              Surely Shirley, minded to this being a compressor over any ignition-spark device, there's no immediate reason to have any space at TDC?
              Last edited by BritCNGUser; 04-26-2020, 06:39 AM.

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              • #8
                Nipple or no nipple, the same amount of gas is compressed. It all comes from stage two; no more and no less. There is no gain or loss of efficiency or heat, either. In other words, the compressor moves the same amount of gas through it in the same amount of time with either piston - nipple or no nipple.
                Last edited by hypermilinggx; 07-05-2020, 06:38 PM.

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                • #9
                  Originally posted by hypermilinggx View Post
                  Nipple or no nipple, the same amount of gas is compressed. It all comes from stage two; no more and no less. There is no gain or loss of efficiency or heat, either. In other words, the compressor moves the same amount of gas through it in the same amount of time with either piston - nipple or no nipple.
                  I see, compression-ratio makes no difference. Well, well? Hence Coltri could leave the crank-throw as it is, make the cylinder 3-4 foot long, let the our piston finish half way up, and there's no loss in efficiency?

                  At that rate we can set the bore length 100 times greater than the stroke, and because "the compressor moves the same amount of gas through it in the same amount of time" nothing would change.

                  We've cracked it! I'm stunned. Normally, it's a wonder I remember to breathe?
                  Last edited by BritCNGUser; 4 weeks ago.

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                  • #10
                    Originally posted by BritCNGUser View Post

                    I see, compression-ratio makes no difference. Well, well? Hence Coltri could leave the crank-throw as it is, make the cylinder 3-4 foot long, let the our piston finish half way up, and there's no loss in efficiency?

                    At that rate we can set the bore length 100 times greater than the stroke, and because "the compressor moves the same amount of gas through it in the same amount of time" nothing would change.

                    We've cracked it! I'm stunned. Normally, it's a wonder I remember to breathe?
                    The newer designed, flat-top piston retains the same bore & stroke, which also leaves the compression ratio unchanged. The lack of the nipple does not affect the compression ratio. The compressor moves the same amount of gas through it with either piston. This is just a simple observation and can be easily proven with a gas flow meter and a stopwatch.

                    A dome vs. a flattop piston will raise the compression ratio of an internal combustion engine, but not a compressor, for there is no compression (combustion) chamber.

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