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look what I found lurking in my 3rd stage head (MCH5)

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  • #31
    Re: look what I found lurking in my 3rd stage head (MCH5)

    Originally posted by trdscfjc View Post
    after another chat with steve i think we have it nailed down to blow by from the 2nd and 3rd stage with the 3rd stage being the likely candidate

    I also spoke with Mike Casey from Lawrence Factor, I sent him and Ray Contreras the video about the new 4th stage valve and piston assembly for the mach 30 (similar to the 3rd stage on the mch5) and am awaiting pricing and more info on a possible retrofit, the mch30 may be slightly longer and wont fit in the mch5, will update when i have more info on this

    i also spoke with Carl from L&M compressors who has experience with every major compressor on the market (Bauer,Coltri, Mako, GD etc...) and he also said that this sound like a faulty ring issue.

    A few other things that i found interesting about the MCH5 is that there is a weak link in the second stage piston wrist pin. We are unsure if coltri has done what bauer has done and beefed it up by using a needed bearing in the wrist pin but its something worth looking into.

    Another thing that i wanted to share was that the newer compressors use a phenolic material for the piston rings as opposed to steel or chromoly. These being much more expensive (about 20$ each ring) but have very good wear properties and they do not conduct heat, this in turn seals better and minimize heat transfer to the gas. If i can run these rings i probably will and report back.
    my thought would be that I want to transfer the heat to the cylinder from the piston so it can be transferred to the abundant air.just my quick thoughts I will have to study on this.

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    • #32
      Re: look what I found lurking in my 3rd stage head (MCH5)

      the real advantage (as i understand it) is that the rings last just as long as the steel/chromoly rings but dont wear the cylinder bore so multiple ring swaps can be made before the need to replace the cylinder

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      • #33
        Re: look what I found lurking in my 3rd stage head (MCH5)

        Technology has come a long way with composite materials. It is my understanding that this is one of the main hurdles in getting a CNG compressor "approved" safety wise; Steel piston rings on steel cylinder walls is supposedly unacceptable.

        trdscfjc, If those rings hold up like they're supposed to, look at it as an upgrade; I noticed in your pictures that your cylinder walls are scored.

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        • #34
          Re: look what I found lurking in my 3rd stage head (MCH5)

          This is the second of these compressors on here to have ring slash cylinder failure in under 5000hrs this is unfortunate on a 10,000 dollar machine. Have to wonder how much of this is a result of going to 3600 in three stages as opposed to 4 and the resulting higher thermal loads.

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          • #35
            Re: look what I found lurking in my 3rd stage head (MCH5)

            Isn't the Coltri MCH5 a four stage compressor?

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            • #36
              Re: look what I found lurking in my 3rd stage head (MCH5)

              Three stage

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              • #37
                Re: look what I found lurking in my 3rd stage head (MCH5)

                Originally posted by flatracker View Post
                This is the second of these compressors on here to have ring slash cylinder failure in under 5000hrs this is unfortunate on a 10,000 dollar machine. Have to wonder how much of this is a result of going to 3600 in three stages as opposed to 4 and the resulting higher thermal loads.

                Carl told me that I am getting close to the due date for ring change. And although the U.S. price may be 10,000$ in the rest of the word it's about 7000$ even if the rings cost me 80$ that's not bad if I can go another 3000 hrs.

                Perhaps the new phenolic rings prove to last longer

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                • #38
                  Re: look what I found lurking in my 3rd stage head (MCH5)

                  Is it okay to change just the rings and not the scored cylinders, too? If the scratches are not too deep, the new, composite rings may seat and seal into the scratches.

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                  • #39
                    Re: look what I found lurking in my 3rd stage head (MCH5)

                    well I have worked on a lot of cng compressors and all but 1 or 2 had metal rings. as far as steel rings on steel walls is bs as there is no 02 in the cylinder you could not light the gas with a match with no air

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                    • #40
                      Re: look what I found lurking in my 3rd stage head (MCH5)

                      Qruling out foreign matter thru the compressor only one thing causes cylinder scoring and ring failures, a breakdown of the lubricant film due to operation outside the thermal limits of the oil. A different ring material may help but the main problem is still the heat.

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                      • #41
                        Re: look what I found lurking in my 3rd stage head (MCH5)

                        Yes this is true and when compressed gas keeps getting recirculated over and over again (due to worn rings) as in my case the thing keeps getting hotter and hotter.

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                        • #42
                          Re: look what I found lurking in my 3rd stage head (MCH5)

                          auto ignition temperature of diesel is 493 degrees fahrenheit obtained with a 15 to 1 compression ratio, your taking gas to a 250 to 1 compression in three stages you can imagine the internal cylinder temps before intercooling, the major drawback of a three versus four stage compressor. Once blowby starts, it is blasting 600 degree gas past your rings and not much surprise the oil film fails.

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                          • #43
                            Re: look what I found lurking in my 3rd stage head (MCH5)

                            On a true heavy duty four stage compressor such as a Bristol, Bauer or Davey pumping clean utility gas rings are a 10,000 plus hour item.

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                            • #44
                              Re: look what I found lurking in my 3rd stage head (MCH5)

                              Would the type of oil matter in this situation or would all types of oil cause the oil film failure?
                              Originally posted by flatracker View Post
                              auto ignition temperature of diesel is 493 degrees fahrenheit obtained with a 15 to 1 compression ratio, your taking gas to a 250 to 1 compression in three stages you can imagine the internal cylinder temps before intercooling, the major drawback of a three versus four stage compressor. Once blowby starts, it is blasting 600 degree gas past your rings and not much surprise the oil film fails.

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                              • #45
                                Re: look what I found lurking in my 3rd stage head (MCH5)

                                No matter what oil was used the excess heat would of certainly caused accelerated breakdown.

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