What's the most common problem when the pump quits. I have a Craftsman 6.5 OHV w/horizontal shaft motor. The pump is attached to the output shaft, or the front of the motor. Model 580.767300
I took the pump face off and I can tell you this, the 3 pistons do move in and out, and the piston seals look good.
I replaced all the O-rings and put the face back on, but absolutely no pressure comes out. Water will stream out the outlet (but w/o pressure) so there are no clogs. Engine runs great. Any Ideas?

Its possible it could be the internal valve that is stuck. It's a regulator valve.

I see a total of 6 check valves in my parts list. Hmmm, wonder if it's worth it. Thanks for getting back to me.

Edit: 4/12 Sold it on Craigslist today. Off to Lowe's. Decided to get the Troy Built 3000 psi model.