PMr720 blew a tube - third row down - second from the left, if I remember rightly - at the throatplate (smokebox end of the boiler barrel) whilst climbing Minvalara bank, way back in the late 80's. I can't find the exact date at the moment.
The crew suspected a problem, and had difficulty in maintaining pressure. Maintaining water was hard to do also, but was achieved. It was inferered that the difficulty was as a result of relative inexperience on the part of the fireman. Full pressure was restored after topping the 251 km (as it should have been able to be).
On reaching Peterborough the fire was dropped, and the loco stabled. The following day, the fireman was determined to find a cause, and prove or disprove his thoughts. On opening the smokebox door, a flood of water escaped, confirming the fears of the crew.
The loco was mothballed and services operated by W901 until cessation of running. Of course, that is another issue, as 901's boiler condition is now listed as terminal.
The loco was subsequently stripped down with an intent to attend to motion and boiler repairs. It was intended to try and raise the capital - never an easy task for cash-strapped STP - to re-tube the boiler. The option of blocking off the offending tube was not considered a viable one - nor should have it been so.
The tender and engine units were separated, the boiler's crinoline and fittings removed, and various motion components removed from the frame.
STP's 50% tender first working had caused significant wear of the lower cylinder crosshead slidebars, and these were removed with the intention of hard-chrome plating and machining. Running a steam loco in reverse causes a disproportunate amount of force to be applied downward to the upper face of the lower slide bar (as in the case of the PMr) or to the upper face of a single slide bar (as in the case of a W). The trouble is, on traversing open surface level crossings when running tender first, enough dust and grit is stirrred up to land on the upper face of the lower slide bar, creating grinding paste - which is why the slidebars wore so badly in such a short operating time. The upper slidebars were in much better nick.
The various motion components were safely warehoused on site. The wheels and general condition of the loco is good - there is little hollowing of the treads, despite the light rail over which the unit had been operating.
The general condition of the unit was a credit to the team - lead with dedication and skill by RJ Yates - that reconditioned the unit in the first place. I wish my work was as good as RJ's. Sadly, little re-assembly or maintenance work was carried out beyond stripping the loco, although the airing-out of the boiler has no doubt saved it.
The locomotive is, as best I know, still dissassembled, but all components should still be on site.
The loco performed well when last I worked it, and should be still considered to be a real chance of running again - if it can ever be relocated to a location suitable for its repatriation - the likelihood of anything ever running again at STP is - tragically - very, very slim.
Last I saw it up close, the loco was in the former machine shop, although I noticed what appeared to be the PMr in the roundhouse when I last passed through Peterborough in daylight - but it is hard to tell at speed.
Those who had the know how and drive to create it in the first place, have moved out of town, and have little to do with STP. The local townsfolk have little interest in STP. The local town corporation had long desired the cessation of train running by STP, in lieu of the creation of a (static and lifeless) museum.
I'm told that approval for the recovery of the track assets has been granted (ie it's to be pulled up) and that this may have already commenced (Can anyone confirm?). The corporation got what they wanted, and it's very regrettable. The Oladdie Hills were a delight to work through, even if hard work, on occasions.