Coltri mch6 air leaking back through the air intake

[lukejjon]

Hi,
I have a Coltri mch6 that leaks air out of the air in-take. I don't know if it does it when it's running, but you can hear it once the compressor is turned off. From what I've readi it might be the 4th stage valve, but I wanted to get some advise before I start pulling stuff apart.
Can any one suggest anything I should check to narrow down the cause if it's not the 4th stage valve?

 

[Agro]

It is definitely not one of the 4th stage valves. I see:
- Inlet valve 1st stage
- one of the cylinders has a large blow by. This means piston does not seal anymore in cylinder, air passes into crankcase and then into air intake

I expect blow by to be the problem, this often happens on a MCH6 after a few hours. In most of the cases it startes at cylinder no. 4, then cylinder no 3.

The 1st stage inlet valve normaly lastes longer than the whole rest of the compressor which means longer than 50 to 100 hours.

 

[lukejjon]

Thanks Agro. According to the previous owner the compressor has only 10 hrs on it, which is why I didn't think it would be worn pistons etc but I guess it's entirely possible the seller didn't provide accurate information.
I think it may have sat for a while without any use - is it possible the rings could be not sealing and need to be run for a while to lossen up (a bit like a combustion engine)?

 

[Agro]

Thanks Agro. According to the previous owner the compressor has only 10 hrs on it, which is why I didn't think it would be worn pistons etc but I guess it's entirely possible the seller didn't provide accurate information.
I think it may have sat for a while without any use - is it possible the rings could be not sealing and need to be run for a while to lossen up (a bit like a combustion engine)?

I don't know. But I've never heard so.

Have a look at the tube coming out of the crankcase and going into air intake. If you see oilflow inthere then you also have airflow. Or take away this tube and check for airflow. If you have airflow out of crankcase then you have blow by.

If the problem is first stage inlet valve then you have no airflow out of the crankcase, air is coming back from 1st stage.

 

[lukejjon]

I don't know. But I've never heard so.

Have a look at the tube coming out of the crankcase and going into air intake. If you see oilflow inthere then you also have airflow. Or take away this tube and check for airflow. If you have airflow out of crankcase then you have blow by.

If the problem is first stage inlet valve then you have no airflow out of the crankcase, air is coming back from 1st stage.

Thanks Agro, that helps a lot. It sounds like I have a blow-by issue. Is there anyway to work out which stage is likely to be issue (hoping it's only one of the stages )

 

[Agro]

Close 4th stage's outlet. Take away inlet tube, add 300 bar to 4th stage's entrance, check for blow by.

Normaly 4th stage is the problem, sometimes 3th stage, hardly ever 2nd and 1st stage.

Instead of checking you can also just exchange 4th stage, cylinder and piston. As far as I know they are cheap.

As soon as Coltri MCH6 is working again, SELL IT. It is a lousy compressor.

 

[lukejjon]

Thanks again for your advice Agro, it's very much appreciated.

 

[Agro]

Let us know what the problem was.

 

[lukejjon]

I haven't fixed it yet, but after pulling the 4th stage apart, the valve was in pieces and the spring was all rusty and horrible. The cylinder wall was fairly badly pitted so I think I've found my problem....
The third stage stage looked ok though.
It looks like I'll be replacing the 4th stage, any suggestions on where to purchase them at a reasonable price?

 

[Agro]

Ersatzteilkit 4 Stufe Kompressor MCH 6 von Coltri

Das komplette Ersatzteilkit für die vierte Stufe des Atemluftkompressors MCH6 von Coltri Passend für alle Variante des kleinen Kompressors Das Kit ist ohne Pleu

www.coltri-kompressoren.de

In the US you might ask Nuvair.

And don't forget: as soon as Coltri is running again, sell this piece of **** and buy a reasonnable compressor.