I have an ir RA330E20 and the piston ring is worn out. Does any one know where I can get replacement part (Ciscoair only services BIG compressors!) I've owned it over 12 years and it has worked flawlessly until recently. It just can't reach the 100 psi cutoff point anymore (I suspect piston bypass cause the reeds are working fine and so id the check valve. But the is "wiggle-room between the piston and cylinder wall.)

Head Gasket
Rocker cover gasket
Inlet & exhaust manifold gaskets
Main and Big end bearings
Service manual Oil filter

Blowing black smoke means fuel mixture is too rich, possible choke is stuck partically closed.
Blowing white smoke especially driving off the traffic lights indicates either worn valve guides or worn piston rings. Valve guides require the head to be removed to replace valve guides.
Replacing piston rings means a major engine repair. It maybe better to get a reconditioned motor than replace worn piston rings because other worn engine parts should be replaced at the same time.

Oil in the air lines indicates you have air pump problems; either worn or broken piston rings or badly scored cylinder wall(s), usually both. You'll have to disassemble the air pump or take it to a service center to find out what's wrong inside pump.

There is no specific sign that says it is time to replace piston rings that I know of. Some signs are drop in compression or power, harder to start, etc. But the same signs could be because of worn valve guides, build up of carbon between valve seat and valve, making the valve not seat properly leaving a small gap and dropping compression. Build up of carbon in the exhaust port could also be a problem making your saw not run right. You might have to take the engine apart and check piston ring gap also the ring might be seized stopping it from moving up and down to follow worn cylinder wall and lowering the compression. Cylinder wall wear could also be a problem. So there is no specific sign that I know of as I mentioned earlier. If you are having a problem with your saw there could be many different causes worn rings are just one. So unless knowing of a specific problem, the above is a general answer to your question about piston rings and what problems they could cause. I hope this helps you.

The C6110 is an oil free air compressor and has a piston ring that needs to be replace as part of regular service.
When the piston ring is worn out it will just keep pumping but it will not go over 80 psi or so because to much ir is passing by the ring.

Here is a parts diagram:
http://shoppingcart.msservicecompany.com/msservice_net/product_files/C6110/C6110_PL.pdf

It sounds like the piston ring DAC-308 needs to be replaced. You can also replace the complete top end.
This is a pretty easy repair and can be done in less that 1 hour.

Sounds like you need to adjust the valves.

after servicing the carb,do u retune it?
blacking around the piston is no big deal for a small engine,as long as the piston rings are in order or in other words it still has compression.

check the fuel supply..
the tank should be airtight...
it is a diaphragmed carby...