Ok I know the tank is a Curtis, do not know if the motor is origional, I'm pretty sure not. I know the compressor is not origional. When you say refrigerant compressor, any idea what it came off? It still gets the tank to 160psi, just takes a while. About 15 minutes from empty. Ran our air nailer all day just fine. But would like to either rebuild, or replace it to get it better. I would like to run an impact off it every once in a while.
From the time and pressure numbers that you posted, I'd say that the pump is working just fine. As stated above it's an antique refrigeration pump; one for which it is difficult if not impossible to get parts for IMHO (BTDT). With the globalization that has occurred in virtually every manufacturing company, trying to get support for 75-year-old equipment is just not going to happen.
Back in the good ol' days, it used to be that you could 1) call the manufacturer/factory, and 2) get a warm body to actually talk to you. If you were nice, they might then 3) transfer you to some old codger that had been with the company since 1922. Once said codger got over his upsetness and grogginess from having been suddenly awoken from his daily nap, he would then 4) dig around in some old parts manuals for you, and 5) come up with a part number. If you were super nice, he would also 6) look up said number for you to see if they still had one laying around or 7) could tell you which regional warehouse might still have one.
Unfortunately, those days are long gone. Sorry. With the performance that it is giving you now, I'd keep oil in the sump and run it. But only after I completely redid the wiring on the unit (and only use with a grounded cord). Does it have a pressure relief valve anywhere on it, as I don't see one in the picture.
