Note that Mr. Austin's post includes a method for hammer-testing of flexible staybolts, s different procedure from regular stays. Earlier in the letter is a comment that flexible staybolts may fail a hammer test if the head slightly unseated in the thimble, e.g. from the result of contraction with pressure relieved and the cap insufficiently secured.

Flexible Stay-bolts are purposely not seated; "run them "in" so they seat, then back "off" 1/4 Turn.

The Hammer looks like the one I used before it was stolen along with my pyrometer.

What is the reason to back them off?

Roger

When the inner firebox gets hot, it expands, causing the bolts to shift very slightly. The shift is an angular shift for the bolts. The backing off gives the bolts a little bit of slack, so that when hot they are properly tensioned, without over stressing them.

Mark, thank you that makes perfect sense.

In a related question, do the ball end of flexible staybolts ever bind into the socket? Given the environment they work in, I would have to think it happens at least occasionally.

Roger