Pressure washers

   I was given a Troy Bilt a couple of weeks ago because it "wouldn't build pressure" and I think I figured out why . There is a ball check vent valve on the HP outlet . The spring holds the ball off the seat under normal hose pressure but as soon as the pump builds pressure the ball is supposed to seal the outlet . Except the ball and spring are missing ... Soooooo , the question is , if I can't find the ball and spring can I just plug the hole ? I think the only difference it will make is that I'll have to hold the wand trigger down while starting the unit . I just replaced the bypass valve because it had a crack on the piston head . I think the missing ball and spring are venting enough pressure that the bypass valve never opens . I'd like to get this unit running , it has higher pressure and flow rate than the last one I got for free .
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Snag
  "They may take our lives but
they'll never take our freedom."
  William Wallace