Compressor not turning freely - NEED HELP

[spyridon]

Hi guys, I am in the process of rebulding my COLTRI MCH6 compressor and I have a huge problem. I get the compressor assembled and when I try to turn it by hand clockwise it turns for a couple of turns (sometimes more and some less) and then tightens, then turns freely again. I am very frustrated! Conrods of 3rd and 4th stages are correctly put (back to back), all needle bearings are new and conrods turn freely on the crank when out, all conrods are new, nothing is left out! It's as if 2 conrods are rubing/touching with each other.

I would very much appreciate any thoughts.

Thanks

 

[bobbyp10]

Strange that it's "

sometimes more and some less". Generally mechanical fouling will be in a very similar or same position and the crank goes through it's 360 rotation.

If it turns fine when out of the block, you may need to look at any interference with the barrels or crank ends, and re-check those needle bearings are correct and all there.

Silly question - Are some of the heads on? Could it just be the compression?

Maybe slowly disassembling part by part, turning the crank after each removal, till you find where it frees up, and investigate there. ​

I'm sure there's a few others here with excellent ideas for you too mate!

 

[spyridon]

Yes it is very strange. The problems start when installing the 1st stage head. When 2nd stage conrod and head are installed all OK, 1st stage conrod all OK then 1st stage head and it starts. What could be wrong with it? Is there maybe a specific way to install the 1st stage cylinder & head or the bearingsto the rods?

 

[CraigAClark]

Did the rods go back together exactly the same way as they were originally? I believe there is a correct "facing". See if Ray can help, he is a Coltri distributor.


Craig

 

[scubashine]

I am not familiar with your compressor, but I do work as a mechanic...

The 2nd stage pumps air to an empty tank when you first assemble and rotate it, so low/no resistance.

You install the 1st stage head, now when you rotate the assembly aren't you supplying compressed air to the second stage for it to compress?

If this is the case, might the increased resistance be caused by the extra effort to compress (100psi?) to (1000psi) in the second stage instead of (1 ata) to (100 psi) earlier?

Just an idea...

Good luck!

 

[spyridon]

Hi mate, good thought but this would be not the case as I have not connected the stages together so each one is independant. Could someone who ownes the same compressor check if the compressor turns normally and with no restriction on both sides?

 

[spyridon]

Hi Craig, the rods, bearings and bushings are all new, this is what drives me nuts! 1st stage was installed exacly the same way as before.

Did the rods go back together exactly the same way as they were originally? I believe there is a correct "facing". See if Ray can help, he is a Coltri distributor.


Craig

 

[spyridon]

I just want to point out that the compressor does this when turning it clockwise and when I turn counterclockwise it turns OK. The thing is that I am afraid to turn it with the motor to avoid damage.

 

[rcontrera]

Well, that IS a strange one. These guys are real basic and easy to work on. And if you don't have the air lines hooked up between the cylinders, I really can't think of what would be causing an intermittent rub. But if you don't get the resistance with the first stage head off, then it is most likely just pressure in the cylinder. The carbon fiber valves are pretty stiff and can hold back a bunch of air. If you turn it a few turns and the outlet fiber is a little stiffer than the inlet one, then it may just take a couple of turns for it to build up enough pressure to "burp" the valve open.

 

[spyridon]

Hi Ray. thanks for coming back to me. The 1st stage head I have is the old one with normal valves, not reed.

Could it be the bearings? The ones I bought new and installed in my rods are TORRINGTON B-188 and the needle is straight between the sides of the bearing. Originaly installed were JL 188 needle bearings and their needle is with conical ends. Just guessing if this could be a problem..?

Should the pump rotate normally on both sides, clockwise and counterclockwise?