The spring is not required. None of my PO’s had surviving springs and the valve worked well. I would suggest for best performance that you remove the piston from the housing and clean everything well. Exhaust pressure forces the valve open and water pressure forces it closed. What you will notice when idling is the piston will reciprocate some which does nothing to hurt performance. The retaining clip is not spring steel, and invariably when you remove it, it tends to bend inward resulting in a loose fit. So prior to re-installing it, bend it outwards a bit for a snug fit.
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