MBMB

When reinstalling my flappy, how much preload should I put on the spring that keeps the flappy closed?

Many thanks.

worf928

Enough that it springs closed. Not so much that the vacuum actuator cannot open it. It's one more turn of the spring than is really easy to do with just the fingers God gave you. (Sorry, I cannot be more precise.) Test with the actuator installed and a hand pump.

MBMB

That's perfectly clear, Dave. The spring will take one turn or two. You're describing two.