Observations and Problems

Oil Conversion

One of the first orders of business that needs done is an oil conversion. The Coltri MCH-5 comes with synthetic Coltri 750 compressor oil (CE-750). It is virtually impossible to find CE-750 and you will end up trying to get it from a dealer. I found a Coltri Scuba Compressor dealer on the left coast who was happy to sell me some until he found out it was for a CNG compressor, never heard from him again. I even contacted Coltri America www.coltriamericas.com and talked with David McKenna about acquiring some CE- 750. Unfortunately for me, Dave was only interested in where I got my MCH-5 and who sold it to me. Well that is a story for another day. I did a little research and decided on Chemlube 810. With that I went to Protecair's website www.protecair.com and ordered up a 5 Gallon pail. It is important to purge out all of the existing oil weather is is mineral or synthetic based. To switch out the oil use this procedure: drain out the old oil and fill with Chemlube 810. Run the compressor for an hour and then change the oil. Then run it for three hours and change the oil a second time. After the second oil change you can run the compressor about 10 hours and change the oil again. At this point the conversion is complete and you can change the oil at the normal 100 hour interval.

Aluminum Intercooler Breakage

My compressor was about 10 months old when I noticed that fill times on the Cavalier were getting up to 3 hours. I also noticed gas smell in the air. After a ton of trouble shooting, I narrowed the problem down to a crack in the aluminum intercooler between the 2nd and 3rd stages. The crack was on the backside so it could not be seen. As the crack got bigger, I eventually was able to hear the leak over the compressor motor and fan. I contacted the seller and he told me some of his other customers were having the same problem. He informed me that Coltri had a Stainless Steel replacement and he had 8 on back order. Well I decided enough of than so I removed the intercooler and TIG welded it. That worked well for about a month and it cracked again. This time I picked up a brass coupler in metric and worked it on to the tubes. After running the compressor, I had to re-tighten the fitting a few times. At this point I began beating the bush looking for a Coltri CNG Dealer. I finally located. GreenLine Fuels which is a Coltri CNG Dealer and after talking with the owner, Justin Beerer, he was able to get me a stainless steel replacement under warranty. The new intercooler was a near perfect fit. I just needed to bend it slightly, however it works like a charm and has not leaked yet.

Here is a poor pic of the crack.
It was not all the way around however
it was cracked for a while.

Here is another pic of the crack.


Here is a pic of me flaring one
end of the cracked inter-cooler

Here is a pic of the inter-cooler.

Gunked up or worn out valves

The MCH-5 CNG compressor lacks the ability to read the pressures in each stage. The only gauge is off the valve body for the high pressure discharge for total PSI / BAR. When testing the compressor for valve wear and functionality, the procedure is to hook up gauges in each stage and read the pressures. Each stage is supposed to have an exact pressure. Some symptoms to look for on the valves would be when it kicks out the second stage pressure switch causing the machine to shut down. Another thing is the color of the oil, since natural gas is a closed system and there is no oxygen we don't get any carbon buildup in the valves. So the valves should hold up for 2000 hours without a problem. It is recommended that the valves be replace every 2000 hours. The only issue with the valves is if there is something caught inside the valve it will let more pressure through the stage than needed and will put more load on the rods. If your machine is venting really bad, when you shut it down, then you have blow by in the rings, causing high crank case pressures. Also the machine will vent when shut down, this is normal ,however high pressures coming off the vent line indicate a problem.

This site was created by Brian McKay 2004-2011, All Rights Reserved. Brian.McKay@littlemetalshop.com