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

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  • #46
    Re: look what I found lurking in my 3rd stage head (MCH5)

    I am the most intrigued by hypermilinggx's question:

    "Does your Coltri have a vacuum pump or at least a crankcase vent to keep a negative pressure in the crankcase? A positive pressure in the crankcase could cause a lot of blow by"

    I had never heard of this concept but did some googling and it was interesting to hear the horsepower gains racers document by running a crank driven vacuum pump pulling a slight vacuum on their crankcase. At least a part of the horsepower increase is attributed to improved ring sealing.
    It sounds like Joe is running his compressor at 2psi and IIRC the parts diagram of the Coltri CNG compressors show the crankcase vented back to the intake of stage one through the oil filler tube. I am guessing the crankcase is thereby pressurized to 2psi (or a little higher with blowby???)

    If rings seal better with a slight vacuum it would seem beneficial to introduce the gas to the compressor at the lowest pressure possible without starving it so that it was actually sucking (drawing a slight vacuum on the intake stroke.) This vacuum should serve to pull a slight vacuum on the crankcase.

    The fuelmaker doesn't have a conventional crankase or piston ring design so it isn't a relevant model to follow. What are other relatively small CNG compressors doing with their crankcase gases? If venting to atmosphere it would amount to a lot of wasted gas. If others are recycling to the intake as the coltri seems to do it would seem to be a handicap in proper ring sealing (if positive crankcase pressure really does reduce the ring seal and increase blowby)

    Are any compressors actually running a vacuum pump to de pressurize the crankcase? If so is the gas recycled back into the inlet from the vacuum pump.? It would seem problematic if a seal on the crankcase failed and the compressor started sucking air into the vacuum system through the failed seal.
    Last edited by karl; 03-04-2015, 11:16 PM.

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    • #47
      Re: look what I found lurking in my 3rd stage head (MCH5)

      Yes, the crankcase is vented back to the intake. You don't want the gas escaping into the atmosphere for financial and environmental reasons.

      I'm sure this is how most other recip. comps. work, I will find out for sure if I talk with Carl from L&M again.

      The crankcase maintains 2 psi as long as the shutoff valve remains open and the gas can vent back to the line. If the valve is shut off to the compressor and there is excessive blow by due to worn rings the gas has no where to go so it builds up in the crank/intake. If you have a 5 psi Wika gauge on your compressor it will cause a pressure spike and break the gauge....ask me how I know....

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      • #48
        Re: look what I found lurking in my 3rd stage head (MCH5)

        I use Summit PGS100 a polyglycol based gas compressor lube. The main advantage of a polyglycol based lube over a diester base is the much higher viscosity index, maintaining a thicker oil film and better ring seal at high temperatures and its much superior resistance to hydrocarbon thinning in gas applications. TRDSCFJC posted back in jan of running this unit 2,000 hrs on Royal purple oil change, I am afraid the extended interval combined with the inherent high heat load of this unit bit him on the backside.

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        • #49
          Re: look what I found lurking in my 3rd stage head (MCH5)

          Well according to Carl from L&M I was due for a ring change anyway, in any case this issue happened after the oil change and I have been running this oil for a couple of years now. IIRC the last oil change was only 25 hours overdue and there was no evidence of any kind that something was a miss (coke/slow fills) at the time I did the oil/valve change.

          I believe that the recirculation of the hot gas over and over caused the coking, would another oil have prevented it I don't know. I have been running my machine pretty hard since December when I got my new truck a big contributing factor is the extended running times, in some cases 12+ hours of continuous use a day.

          What I think would be a good idea is some sort of a flow regulator on the tube that leads from the crankcase to the intake that would give you a idea on how much blow by you are getting so you can see a decline in efficiency and fix it before it causes a major failure.

          I'm approaching 3000 hours. still very much satisfied with this machine, it has paid for itself many times over though I think with a few tweaks it could be better.
          Last edited by trdscfjc; 03-05-2015, 02:16 AM.

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          • #50
            Re: look what I found lurking in my 3rd stage head (MCH5)

            20 posts ago i told you that the rings were wore out. you can easily see the scored cylinders. I would not just replace the rings you need cylinders too.

            DAS




            Originally posted by DAS View Post
            wow that is a lot of crud. city gas no way contains that much oil and dirt.most likley it is oil from the compressor coming past the rings.sounds like the compressor is getting wore out.rather than using the trial and error method the compressor should be sent back to the factory for evaluation and repairs by a properly trained person.


            DAS
            Just my uneducated opinion

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            • #51
              Re: look what I found lurking in my 3rd stage head (MCH5)

              Wasn't trying to bad mouth your machine, glad your happy with it. But the part where a 7000 dollar machine pumping 2 gge or less per hr pays for itself " many times over" in 3000 hrs that math just doesn't add up.

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              • #52
                Re: look what I found lurking in my 3rd stage head (MCH5)

                Joe, I'm curious about information you get on re ringing your compressor if you use metal rings.
                specifically do you need to run a dingle ball hone through the bore to crosshatch or break the glaze on the the stage 1 and 2 cylinders?

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                • #53
                  Re: look what I found lurking in my 3rd stage head (MCH5)

                  Well the cost of gasoline vs cng pumped from the house it's easy to see the savings....I was filling the gas tank every 3 days at 70$ a tank on gasoline, my monthly vehicle natural gas bill is about 70$

                  70$ vs 700$ a month x 4.5 years, that's not counting the other honda civic that I picked up. It's easy to see how the machine has paid for itself many times over.

                  DAS sending the machine back to the manufacturer is not an really an option and although frustrating at times I am glad I have been able to get to know the inner workings of this machine better. Perhaps if steve had not been there to help me I would of had to send it out somewhere for repair. So much appreciation for his patients and guidance through this issue.




                  Karl I'll probably just wire brush the cylinder a little bit to give the rings something to bite into, it's going to be a temporary fix until I get the new head/piston assembly.
                  Last edited by trdscfjc; 03-05-2015, 10:49 AM.

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                  • #54
                    Re: look what I found lurking in my 3rd stage head (MCH5)

                    3000 hrs x 2 gge equals 6000 gge divided by 54 months is 125 gge a month equals 700 dollars worth of gasoline? Does not compute

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                    • #55
                      Re: look what I found lurking in my 3rd stage head (MCH5)

                      the 125 GGE is on a civic and the 700 is on a truck that gets horrible mpgs on premium fuel also factor in the high gas prices in ca (I remember paying 5$ a gallon)

                      I will update when i get the rings installed and report back
                      Last edited by trdscfjc; 03-05-2015, 09:04 PM.

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                      • #56
                        Re: look what I found lurking in my 3rd stage head (MCH5)

                        Back on topic, I received pricing today for the 1st and 2nd stage rings from ray, however as of Yet It Looks Like the third stage rings are not at rays disposal only the entire 3rd stage piston assembly at a cost of North of 300$

                        If I can get the individual rings from Lawrence Factor I will, at least until I can get the new head and piston assembly seen here https://m.youtube.com/watch?feature=player_detailpage&v=ou6VMq-sDfk
                        Last edited by trdscfjc; 03-06-2015, 10:16 PM.

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                        • #57
                          Re: look what I found lurking in my 3rd stage head (MCH5)

                          I am following this thread with great interest, I'm sure Coltri redesigned the new 'Red 3rd Stage" with good reason, so it can only help, but what has you thinking it will solve your issues?

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                          • #58
                            Re: look what I found lurking in my 3rd stage head (MCH5)

                            well, it seems its time for new rings if i have a choice of paying 300 for a new piston and ring assembly or pay a little bit more for a completely new (upgraded) assembly (that includes the new head/valve/piston) then i will get the upgraded version

                            when mike at L.F. showed this video to his lead engineer/mechanic he thought it was better then sliced bread and said something to the effect of "this new assembly solves many of the problems associated with the old valve/head" so looks like they did something right

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                            • #59
                              Re: look what I found lurking in my 3rd stage head (MCH5)

                              I feel for you... OK, frankly I agree with your "While you're on" logic. It looks like it is more than just a new head, looks like the barrel has been changed too, but I'm digging for more info now.

                              I trust you found the new Parts manual showing the 'Red Head' I tried to attach, too big.

                              See it here:

                              http://www.aerotecnicacoltriasiapaci...list_it_en.pdf

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                              • #60
                                Re: look what I found lurking in my 3rd stage head (MCH5)

                                new_kit_head_3rd_stage_mch_811131618.pdffound this E-Flyer
                                http://www.coltrisub.it/MAIN/IMGS/NE..._811131618.pdf
                                Last edited by trdscfjc; 03-07-2015, 06:29 AM.

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