Coltri mch6 air leaking back through the air intake

[zider]

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?

Do some searching related to the MCH-6 and you will find that water build up is common if the pump is left idle. It's really a design flaw as water will settle in the oil sump and corrode 4th stage components if its left idle for any extended period of time. I believe that Coltri has moved to a stainless steel MOC for the 4th stage to help combat this issue. Users recommend running these units regularly during downtime (i.e. through winter months) to prevent corrosion or doing an oil change before storing the unit away.

I agree with others that this isn't the best compressor, but it works well for folks like me who only do a few fills here and there. I follow the recommendation above and simply run the compressor up to pressure for about 5 minutes once a month. So far I've seen no issues. Good luck!