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Coltri diagnostic, (summary to "lurking" thread)

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  • Coltri diagnostic, (summary to "lurking" thread)

    This is the first 10 pages of the "look what I found lurking" thread...I kept the highlights that I thought were relevant
    __________________________________________________ ________

    Think this may of been contributing to my slow fill times.


    This is the 90° fitting on the belt side (back), 3rd stage connects the the horizontal Intercooler tubing to the head

    Used a brass wire bore brush and cleaned it and the head out, still waiting to see if the fill times are better


    I have tried everything I can think of.
    Still only getting 1.75 cfm...added the crush washer to the 3rd stage as well...sigh

    I'm sure I'm missing something but not sure what it is, I have changed every valve in this thing.

    This is the second stage

    This set to the right level, not sure if this would have anything to do with it (I'm running out of ideas)


    Back together again...


    Looks like I'm getting a slight bit of interference from the valve (likely due to the washer pushing the valve out ever so slightly, I do not see any marks on the piston itself or the valve so for now nothing is actually hitting



    Cleaned out the intercooler tube and it was actually pretty clean

    When I am not compressing any gas and I vent the discharge to atmosphere I'm getting 3.5-3.75 cfm (normal) but as soon as it starts compressing the flow comes to a crawl exponentially (higher the discharge pressure the slower it gets)
    All the valves have been replaced along with a new belt. This is a mystery.


    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 mch 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 sounds 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 needle 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.


    Originally posted by cngtennessee View Post
    I thought this was the redesign of the 3rd stage. I believe Nuvair is selling these kits for around 600 bucks.


    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.


    new_kit_head_3rd_stage_mch_811131618.pdffound this E-Flyer


    Here is the part number of the Lawrence Factor ring set I am using in my MCH5 compressor. NP-2211-0376A Link to site:


    Originally posted by alpacafarmer View Post
    How much where the rings?
    1st stage
    Piston ring set. (60mm)

    2nd stage
    Piston ring set. (36mm)

    3rd stage cost is 48$ hopefully they ship out tomorrow morning

    thanks Dave

    Originally posted by karl View Post
    This would be a great chance to put a flow meter on your crankcase and get a baseline on blowby with worn rings. Then rering one cylinder at a time , taking blowby readings before reringing the next cylinder. I am curous if one cylinder is contributing more to the blowby than the other cylinders.

    Let us know how it goes reringing yout third cylinder. I pussed out and bought the entire assembly as I was predicting I would break those tiny rings while installing.

    I am also looking for more clarity on the need (or lack thereof) for breaking the glaze on cylinders 1 and 2 to get the rings to seat properly. My local machinist with 40 years in the trade recommended I run a dingleball hone throught the cylinder to improve ring seating.

    It is tough to find a dingleball small enough for cylinder 2. I found one at the motorcycle shop for 50 cc cylinders.
    I assume these rings are cast iron? Does anyone know?
    The only rings I that I thought would seat without glaze breaking are chromemoly rings in racing 2 strokes but the recommended replacement on those is less than 50 hours.

    Good luck with it.


    Back a few pages I mentioned that Carl from L&M compressors told me that the weak link on the mch5 was the 2nd stage wrist pin....he wasn't kidding

    Going to take another day or 2 to get to the local bearing shop for a replacement needle bearing and wrist pin, then I can replace the rings



    More pictures of the carnage, need some help identifying the brand name of this piston I assume it's a European manufacturer


    Originally posted by cngtennessee View Post
    This is exactly what happened to me when I experienced my 3rd stage valve failure. The following pics are what was discovered when I took the crankcase down. I agree with Karl, remove the compressor and take er down. At the very least the metal shavings from your wrist pin need to be removed from the bottom of crankcase. If the wrist pin is that badly worn, you will more than likely have a worn 2nd stage sleeve on your crankshaft.

  • #2
    Re: Coltri diagnostic, (summary to "lurking" thread)

    PAGES 10-20


    Originally posted by cngtennessee View Post
    This is what my wrist pin looked like when I had my issue. Also...these are the service intervals that were sent to me by Nuvair pertaining to the MCH5.

    As stated earlier (from Carl from L&M) the weak link on the mch5 is the 2nd stage wrist pin.
    Don't know about you guys but I am going to replace the second stage wrist pin and bearing every 2000 hours from now on



    Got the pin from L.F. sourced the bearing locally for 6.50$....nuvair wanted 55$

    Second stage wrist pin/ bearing and rings replaced, still getting 1.5 cfm above 3000 psi....The Mystery remains...

    Going to replace 1st stage rings tonight, that's the only thing left

    I was asked about the method for removing/installing old/new needle bearings for the second stage while the rod is still attached to the crank

    Credit goes to steve for walking me through this

    As you tighten the bolt the 12 mm socket pushes against the race and pushes the needle bearing out of the connecting rod and into the 19mm socket, this is done after the wrist pin is removed (i just put the old one on there for reference)


    This is what is used to press the new bearing (evenly) onto the connecting rod, you may need to use more then one bolt for this.

    If the threads do not reach all the way down the shaft, i have one bolt that lets the bearing go about halfway on and another to fully seat the bearing


    i am using grade 8 bolts for this not sure if this is necessary but they were only a little bit more and im not sure how much stress it actually takes to remove these things


    Thought there was an off chance that my meter could be maxed out so I turned on every gas appliance including fireplace and outdoor fire pit to see if my cfm would remain constant or jump (as it should) with everything on it was flowing 7 cfm. ...with just the compressor running it's the meter is working properly

    Also with everything running I was still getting a solid 2 psi on my intake pressure gauge (that's good)

    I want that newly designed 3rd stage piston and head assembly ASAP



    These are the current pressures, the intake pressure gauge is off by 1 psi (I need to recalibrate it)


    I'm curious,

    Brit, if you vent the discharge to atmosphere and you don't compress anything what is your cfm draw from your meter?

    If it's like mine it will be pulling about 3.25 cfm...let me know


    Originally posted by rcontrera View Post
    Oil is actually fed into the compressor through the first stage as well as the third stage. On the first stage, there is a line that goes from the sump to the suction of the first stage. This top lubricates the rings and that lubrication carries on to the second stage. On the third stage, the pusher piston splashes oil into the third stage floating piston and excess drains back to the sump. However, there is always going to be some carryover. In an air system, there is a moisture separator that pulls off moisture and oil from the second and third stages before it hits the filter chemicals.

    New parts arrived, got a 1st stage wrist pin and 2 sets of rings


    Got the cylinder deglazed today, also pulled the 1st stage wrist pin, it has a slight gall but it's in great shape compared to the 2nd stage wrist pin.



    Here's how I pressed the old 1st stage bearing out


    This one (1st stage wrist pin needle bearing) is a Torrington HK2020B....5.99$ at my local bearing shop



    Originally posted by rcontrera View Post
    There is always going to be a little drop from low to high pressure. However, that really is excessive. My littlest air compressor is 3.5 CFM and at 4500 psi it drops to 3.1-3.2 CFM. The first suspects are valves. Rings are usually pretty easy to tell since it leaks into the sump and you can tell when pressure has increased by just holding your hand over the oil tube while it is pumping.

    Originally posted by cngtennessee View Post
    I have now pumped approx. 160 GGE's of CNG while using molecular sieve 13X in my prefilter(filter set up prior to NG going into MCH5) and the results are outstanding. In the past I would get 1-2 ounces of oil/moisture coming from the discharge filter attached to the compressor. I have not had any moisture/oil since using the 13X. I suggest after getting compressor fixed that you use the 13X.


    • #3
      Re: Coltri diagnostic, (summary to "lurking" thread)

      Page 20-30


      [QUOTE=rcontrera;70505]Just a few points for clarification:
      1. The internal parts for the MCH13 and the MCH5 are mostly the same ... bearings, rods, pistons, cylinders, etc.
      2. MCH13 and the MCH16 are both three cylinder, three stage compressors and are rated for continuous duty up to 5000 PSI.
      3. The MCH6 is a four stage compressor rated for intermittent duty up to 4800 PSI.
      4. Intermittent/continuous duty has nothing to do with the number of cylinders. It is a rating of the bearings and sump size.
      5. Compressors that run slower and/or cooler will last a LOT longer as long as the proper lubrication is used
      6. There really aren't any U.S. dealers for the MCH5 CNG machine straight out of the box from Italy since they haven't jumped through hoops for whatever restrictions are imposed by the Feds/States.


      Originally posted by karl View Post
      Britcnguser writes,
      "Only I'm not sure I know what speed I am supposed to be seeing and at what pressures anyway.
      My mch-13 runs approx 95 psi on the first stage, approx 600 psi on the second stage. These measurements come from $20 Wika liquid filled gauges that are presumably accurate for identifying changes in operating parameters but doubtful they are precisely calibrated.
      I haven't calculated the exact rpm based on motor speed and pulley size but my unit was sold as a max air 90. I am a little concerned that max air may be running the compressor at a higher speed than coltri designed it for as they rate it at 10.8 scfm and Coltri rates it at 7.5 cfm.
      I do know that I get .5 cfm blowby with my variable frequency drive set at 60hz (full motor speed) and the blowby flowmeter stays virtually unchanged if I drop the vfd down to 20hz. 1st and 2nd stage pressures remain unchanged as I vary the speed. The only thing that seems to affect the pressure is the pressure the stage upstream is pumping at. With a priority/backpressure valve installed on my output the compressor always runs at a constant pressure on the third stage hence the lack of pressure variation in my case.

      Ultimately I prefer to run the compressor at a slow speed to keep temperatures and noise level down. I am not especially concerned with pumping rate as long as it does it in a reliable and predictable manner.
      Coltri specifies the mch 13 run at 1350 rpm and the mch-8 run at 900 rpm. They are both the same pump so I don't see any issue with running mine at reduced speed.

      If Ray Contreras doesn't often see bearing failures on his Coltri'ss I am guessing Maxair badged Coltri's like my own trash their bearings due to the increased volume Maxair sets them up for. I plan to calculate my compressor speed at my first opportunity.

      It seems like Britcnguser and Trdscfj both have blowby issues that are difficult to pin down. I have found the compressor inlet is very sensitive to changes in pressure and restriction and changes in those parameters have a profound effect on the blowby. Running a restrictive supply line or solenoid gas valve regardless of pressure can double my blowby to 1cfm.

      Anyone running an inlet filter would do themselves a favor if they added a blowby flowmeter and checked the blowby prior to installing the inlet filter and after installing. It doesn't seem logical to me but I find that even if you have a gauge showing the inlet pressure remains unchanged, adding additional elements to the supply plumbing will increase blowby.

      All I can speculate is that the pulses on the compressor inlet may act like a tuned exhaust on a two stroke or a tuned header on a four stroke and the volume and size of the supply piping may assist or obstruct the incoming gas in maintaining a steady flow.


      After a quick trip to my local harbor freight I got a arbor press, bearing and seal driver set and a bearing separator I was able to get the race's out (using the 44.5mm driver)

      more updates to come....been taking it easy this week but going full bore next week

      Originally posted by rcontrera View Post
      There IS actually a tube that runs from the sump to the intake of the first stage so that it can suck up the oil mist. This is called top lubing and is what will get some oil to the top ring or two on the piston. That bit of oil is moved to the second stage for top lubricating there and then to a separator to remove the excess. The air then goes to the third stage where oil is "splashed" into the lubricating area and there is a drain like to allow excess to flow off and back to the sump. Oily, wet air is then sent to a coalescer where it it is battered around and most of the condensate is removed. From there it goes to a chemical tower where the remaining oil and water is processed/removed.

      Got more spare parts... 3x crankshaft bearing, 3x crankshaft bearing spacers, 6x 1st/2nd/3rd stage wrist pin bearings, 4x main shaft bearings (front and rear),2x rear main oil seals ...265$


      Just figured since I got it out gona change everything...

      Also found this in a box on my porch...



      Just a quick but important note about the crankshaft bearings...

      These are no longer produced by INA or FAG as far as the shop was able to find, the only company making this bearing is IKO out of Japan (very high quality)

      The main hub for my bearing supplier did have them in stock so not really a issue for me but they did have to do some digging to find out what it was as there was no part numbers on the oem bearings, these IKO's are marked RNAF354716


      Originally posted by cowboy View Post
      I do know if the third stage pressure backs up in to the second it will wipe out the rod. this is what happened to daves compressor.

      Upon reassembly I found that the wrist pin was rather tight in the first stage piston, only way I was able to assemble was to press the wrist pin in with my arbor press and then stick it in the block and then install the crankshaft (threading it through the big end of the already assembled connecting rod/piston assembly)

      Despite the order of assembly in the coltri videos you sometimes need to get creative.

      Just a tip if anyone runs into a similar problem

      Another thing...
      Pay close attention to the assembly of the bearing races on the big end of the connecting rods.

      They should stick out equally on each side, only way to do this is to have some sort of relief on the backside of your press, this allows the race to pop out the other side....again make sure they are equally sticking out of each side.


      Originally posted by BritCNGUser View Post
      I had the same issue with my 2nd stage gudgeon/ wrist pin. Used a socket slightly smaller than pin diam and a long nut & bolt thru' the lot with a larger socket at the other end all acting as a puller. It is an interference fit but er... tight. First stage was the same.


      • #4
        Re: Coltri diagnostic, (summary to "lurking" thread)

        Pages 30-35


        when reassembling make sure to press the rear bearing in fully (i used a arbor press) and then make sure the race on the crank shaft is full inserted into the bearing before final assembly otherwise there will be alignment issues when installing the cylinders


        After a month long vacation I got my machine running 3 cfm at 1000 psi 2 cfm at 2500 psi still testing to find flow at 3600 will update. ..I have not installed the red head. ..yet


        called nuvair, the fittings that came with the new head are for the new style mch5`s, my machine is an older model and the new fittings will not work with the old style intercooler tubes, [email protected] has been very helpful in getting this sorted and has come up with some options for me to get this new head working on my machine....fittings should be shipping first part of next week


        just got back from Nuvair, 230 miles (round trip)....I was told over the phone to not drill/tap the new red head so I loaded up the compressor in my truck and drove it to Nuvair so they could get a first hand look at what I was dealing with, they said they could fit the new head and do the necessary modifications for 190$, went for a long lunch and came back to a freshly installed red head mch5.

        Pumping efficiency is much better I am now getting 3.25 CFM @ 1500 PSI, 2.75-3.0 CFM @ 3500 psi, so the saga is over it not sure if it was the cylinder or the valve or the rings in the old style head/piston assembly but the newly designed valve/piston/head configuration seems to be the winner... I will update on how things look down the road, but for a 3500 HR. machine im very pleased with this output


        • #5
          Re: Coltri diagnostic, (summary to "lurking" thread)

          Some pictures of the red head and the modifications.

          The head comes with straight compression fittings X metric tube

          The older coltri mch5s (2011 build date) use 90° fittings on the head, Nuvair modified the head by tapping it so it will bolt in with the hardware that my machine was originally equipped with.

          Also the rear/top lip of the head needs to be cut off so the 90° fitting can be screwed in.





          This picture is the modified head installed and a unmodified head sitting on top

          Attached Files
          Last edited by trdscfjc; 08-06-2015, 10:55 AM.


          • #6
            Re: Coltri diagnostic, (summary to "lurking" thread)

            got about 10 hours on the new rings and it seems that efficiency is up, I assume the parts are breaking in and sealing tighter

            Its now pumping at a solid 3.25-3.5 CFM @ 3500 psi


            interstage filling pressures are as follows:

            Current pressures, my intake gauge still needs recalibration (reads 1 psi too high)






            Final discharge pressures
            Last edited by trdscfjc; 08-07-2015, 11:20 PM.


            • #7
              Re: Coltri diagnostic, (summary to "lurking" thread)

              So 2,500 to 3,000 hrs would be a good rule of thumb as to major overhaul time on these compressors


              • #8
                Re: Coltri diagnostic, (summary to "lurking" thread)

                I don't think that a major overhaul is needed at 2500-3000 I just did mine because I had mine apart and figured why not...The only thing in need of extra attention is the 2nd stage wrist pin/bearing.

                Ill report back at 6000 hours and let everyone know where im at, I didn't see anything in the bottom end that looked suspect or on the verge of failure.


                • #9
                  Re: Coltri diagnostic, (summary to "lurking" thread)

                  Great update....thanks


                  • #10
                    Re: Coltri diagnostic, (summary to "lurking" thread)

                    When your forced to disassemble your compressor for very low pumping rate, and have to replace entire third stage and second stage wrist pin and bearing, its rebuild time. Any time you do a major rebuild on a piece of equipment not every moving part is worn out but you address all areas at once and skip the piecemeal" replacement on failure" and keep the equipment in good order.


                    • #11
                      Re: Coltri diagnostic, (summary to "lurking" thread)

                      Yours is the third of these that i know of with a bearing failure under 3500 hrs, and i havent been exposed but to 4 of them total. I would give serious thought to dropping the inlet pressure to 1/4 psi and slowing the unit down about 20%. Would increase fill times some but would lower the stress on the overloaded second stage .
                      Slowing the fill would also give your tank more time to dissipate heat and result in a better fill.
                      I think these are great little compressors they just pushed the envelope on speed , and inlet pressure trying to reach for that 2gge an hour for add copy.


                      • #12
                        Re: Coltri diagnostic, (summary to "lurking" thread)

                        the 2nd stage w.p. and bearing can be changed relatively easily and doesn't require removal of the compressor from the frame, i really enjoy my fast fill times. For me it works, if i have to spend 30 min to a hour every 2000 hours to change out the w.p. and bearing at a cost of 14$ per bearing plus the pin is not a big deal. for others it may be something to consider (but i doubt it)

                        As far as heat dissipation is concerned if i am ever going somewhere where i need to get the max range on my vehicle i just wait till the morning (after the tank has had several hours to cool) and turn the compressor on again and top off the tank (takes about 15 min.) however this is a very rare occurrence, maybe 5 times a year for me.
                        Last edited by trdscfjc; 08-19-2015, 04:36 PM.


                        • #13
                          Re: Coltri diagnostic, (summary to "lurking" thread)

                          If I have to get the absolute max range out of a fill I do exactly the same. Most times I don't bother, but when needed, last thing at night my pump goes on, and then in the morn with the pump now stone cold, I run it up. This for the 15 odd mins it takes to get that extra 'nth' of fill.

                          Now "trying to reach for that 2gge an hour for ad copy. "
                          Whilst containing undoubted wisdom, I don't suppose you realise why I had a chuckle. I nearly spat out my tea.I see many on this forum write similar stuff, so i will try.
                          I can assure you that no Italian in his right mind would be thinking in terms of a GGE in anything. He has likely heard of a gallon… just. Maybe. So, best we leave alone the American version of one. So he will certainly never ever have heard of a unit of measure derived from such a unit. Especially when the MCH5 was not designed for Americans. His mind would need to make the four to five leaps to get to the one you made in one. Yet the actaul point stands. He was designing to his marketing department's demand for 5m3 or whatever, so running to say 20% less has to be good. Very good.

                          (I had to smile, and I don't suppose you understand why.)

                          I have to say, 'faster is better' is great, but more often if my pump took an hour longer to fill I'd not care. It would still be filling at decent times over those idiot Phil and FM joke-pumps. And if it saved the pump somewhat, I might care very much. I will look into this. Would slowing it hamper the splash-lube any I wonder? I suppose even if it did, the pump rather than having its nuts thrashed off , is now cruising, so the need for the lube is likely reduced by a greater factor than any hampering.

                          And with my supply-pressure on the ragged-edge of dealing with an MCH5 anyway I kill two birds with one stone. It could make real sense. I've never played with Speed Control. Is it simple?
                          Last edited by BritCNGUser; 08-21-2015, 11:56 AM.


                          • #14
                            Re: Coltri diagnostic, (summary to "lurking" thread)

                            I think jthompson was looking into adjusting his speed drive, maybe send him a pm


                            • #15
                              Re: Coltri diagnostic, (summary to "lurking" thread)

                              " those idiot phill and fm joke pumps" I would go easy downgrading another mans product, you two just spent the last six months, and a sizeable amount of money trying to get your compressors working correctly.