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The screw was tightened too much at assembly!! Do you have a manual? Go get a Craftsman for around $100

I had a craftsman oilfree type that ate 4 of those. Horribly made in my opinion. Got a speedaire oil type from a cabinet maker a couple of years ago and have been happy ever since. On my craftsman the whole pump assy was held together by this little screw on the top of the connecting rod, seemed really cheap to me. So now I use the regulator from it on my little airbrush compressor and I might use the 3.5 motor to make a dust collector......maybe someday.

Good luck