Part 13: Wheels, axleboxes, frames and tender—June 2001


After discussion within the PRR Locomotive Department, it has been decided that both cylinders will be replaced. Moulding for those continues.

The gas ring apparatus heating a tyre, prior to the wheel centre being slipped in


The tyres on the tender wheels needed to be replaced, and after the removal of the old tyres, and cleaning of the wheel centres, the time came to fit the new tyres. The age-old method of heating the tyre to shrink it onto the wheel centre had to be revived, and SteamRanger had built a large gas ring for doing the same job to their locomotive 520 a few years ago. We needed to make our own, due to having far smaller wheels, but the principle was the same. After design started early Wednesday morning (13th), construction of the ring took place through the day, and the first tyre was successfully shrunk on at 3.30pm. Three more were done by PRRPS volunteers during the regular Wednesday Volunteers Night, and the remaining four were completed on Thursday 14 June.

The process is quite simple. Prior to heating, the wheel centre and the new tyre must be machined such that the tyre's inside diameter is slightly smaller than the wheel centre's outside diameter. This difference causes the tyre not to be able to be fitted, but once it is fitted, means that it is held on there, and will not come off except in extreme circumstances. To get the wheel centre into the tyre, either the centre must be shrunk, or the tyre expanded. Considering the cost and quantity of liquid nitrogen (or similar) that would be required to cool the centre enough, it is by far easier to heat the tyre.

Heating the tyre takes between 10 and 15 minutes with the gas ring, which causes it to expand enough that the centre can be placed inside it with an overhead crane, and the whole lot allowed to cool. In the cooling process, the tyre shrinks back to near its original size, and in the process, clamps itself to the wheel centre. Care must obviously be taken to ensure that the tyre and centre line up and sit together properly.

Pouring one of the axle-box liners, Thursday 14 June


After the torrential rain on Wednesday 8 June, and other water related disasters, all of our moulds prepared for new bearing brasses were ruined by the flood waters.

Failure of the cooling tower (water leaks from the closed water circuit) on the induction melting furnace meant that the old oil fired pit furnace had to be resurrected. Thursday 14 June saw this do its first melt in nine years, with the manufacture of the first half of a set of phosphor-bronze liners for the tender axle-box slides. The furnace sounded just like our oil fired T class loco (and smelt much the same!)


The new frames are currently being machined, and following completion of that, they will be assembled.

Machining the new NM frames


As mentioned in an earlier installment, the whole tender tank is to be replaced. Construction of this is being done at Port Adelaide TAFE campus, and is well underway.

New tender tank for NM25, under construction at Port Adelaide TAFE, 1 June