# IMC-ATLAS COPCO T35/T39 leaking air from oil breather



## Trev B (Jul 15, 2020)

I'm trying to find out what the piston ring gap would be on the high and low pressure sides of my 2 stage T35/T39 IMC-ATLAS COPCO. The bore on the high side is 2.2" the low side is 4.120" not sure if i need over sized rings or not either. Ive been getting pressure blowing by the rings and adding pressure to the crankcase. The pressure is blowing out the oil breather.

Thank you for any assistance with this.


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## stevon (Mar 5, 2019)

Trev B,

Is the bore worn or tapered? any deep scratches on cylinder wall or pistons? rings could be gummed up and not expanding as well. Sounds like you need a tear down to see what the issue is

Stephen


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## Trev B (Jul 15, 2020)

Thank you for your response Stephen, there are scratches on cylinder walls. The rings are free and I will be checking for taper early next week. I have it tore down. I can't find much literature on the specific bore size so I know what is in tolerance.


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## stevon (Mar 5, 2019)

Trev B,

Yeah, you would need to know the acceptable bore size and wear limit, just like a car engine. Can you borrow a bore gage? some scratches are normal as long as they aren't too deep, pistons wear out too, especialy the high pressure side.

Stephen


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## Trev B (Jul 15, 2020)

I have a dial bore gauge coming on Monday. The scratches may be .001-.003 deep.


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## stevon (Mar 5, 2019)

Trev B,

I see the specs on this website:


https://mastertoolrepair.com/images/Pump%20and%20Unit%20Specs.pdf


in the "overhaul" section.

Many years ago I rebuilt a 2 stage Kellog American, the high side was wasted. My machine shop had a nickle iron sleeve and they re-sleaved it, sized to a new piston. I was lucky "Scotty" (shop owner) took good care of me and did it for cheap back in the eighties. Guess you would have buy a new cylinder now

Stephen


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