December 2025 including work up to the end of the year.

As is becoming a tradition at C2 working parties, this one started with Andrew and Dave setting up the crosshead assemblies (including piston and piston rod) on the Archdale milling machine. With the slippers whitemetalled, it was now time to machine them to their final dimensions.

A morning's work saw the Fireman's side crosshead assembly set up true on the milling machine. The slot in the bottom slipper was already the correct width, so Andrew was very careful not to machine any additional material off the sides. But we had left several millimetres on the depth of the slot, so Andrew could take an initial cut to flatten the surface, before using this as a datum to work out how much packing to put in place to ensure that the finished surface is parallel to the piston rod. This worked well, and by the end of the day milling of the Fireman's side bottom slipper was finished.

The Driver's side crosshead was tackled the following day. Although the process above was repeated exactly, we found it very difficult to align the bottom of the slot in the slipper with the crosshead. Each time a cut was made, the alignment was re-measured and found to be very slightly out. The packing was corrected, another cut made, and the error persisted. After several more attempts, we concluded that there must be some play, either in the crosshead assembly (although we tested it and everything appeared tight) or in the milling machine (if so, why did it not show up for the other crosshead?). Eventually, after determining that the misalignment was comfortably less than the clearance between the slipper and the slidebar, we decided to concede defeat and accept the error. Somewhat frustrating, but unlikely to be of any consequence.

The top slippers will require a different milling set up, so Andrew started by taking a shallow cut on both top slippers to provide flat surfaces to measure against. At this point he was rather bored of working on the crosshead slippers, so moved onto other tasks. We should get the milling of top slippers finished at the next working party.

With the motion progressing well, we wish to know the exact dimensions of the connecting rod big end bearing covers (which control the lateral alignment of the big end bearings) and the little end bearings (which do the same at the little end). This requires us to know the precise lateral alignment of the crossheads and driving crank pins.

Clamping one end of a long parallel bar to the side of one of the slidebars, and placing the other end adjacent to the relevant crank pin, allowed a measurement to be taken to a known position on the crank pin. Comparison of the results taken for both sides of the engine suggested a significant error on both sides. At this stage we began to doubt the accuracy of taking measurements this way, since even the minutest alignment error of the slidebar will be amplified by the distance to the crank pin (which is five feet away) and will result in a significant measurement error.

Given that it is the alignment of the connecting rods which we were trying to determine, Erle suggested fitting the connecting rods themselves, and measuring lateral clearances at the big and little ends. This would require us to fit the roller bearings to the big ends, but would give us a more direct measurement system. Dave agreed that this was a good idea, so work progressed towards this objective.

The big end bearings each comprise a pair of cylindrical roller bearings separated by 2mm thick spacer rings. Erle found some steel in our 'odds and ends' stack (quite possibly the same billet which Chris used to make the spacer rings for the coupling rod roller bearings) and turned up four spacer rings.

Dave spotted that there should be grease nipples fitted to the big ends of the connecting rods to lubricate the big end bearings, but these had never been fitted in China (which might explain the extreme wear on the return cranks which are adjacent to the big end bearings). Erle found a 1/8" BSP tap while Dave found a couple of 1/8" BSP grease nipples in stores, and soon they were fitted.

Cylindrical roller bearings each come in two parts; an outer race with the rolling elements assembled into it, and a separate inner race. These need to be pressed into the connecting rods and onto the crank pins respectively.

The big end bearing outer races project from the surface of the connecting rods by 2mm each side. Ideally we would align the races using the bearing covers, but since we are trying to determine the bearing cover dimensions, these are not yet available. So Erle found some 2mm thick shims to place under the edges of the connecting rod big end. The connecting rods were carried to the hydraulic press and the first one was placed on the 2mm shims. Erle and Dave then pressed the first bearing outer race into place, followed by the spacer ring and the second bearing outer race. The procedure was then repeated for the second connecting rod.

Three years ago we fitted most of the coupling rod inner races to the crank pins using a press tool, but that was very hard work. The larger driving crank coupling rod bearing inner races refused to be pushed on, and so we had used the oil bath, which made the task remarkably easy. So, for the connecting rod big end bearing inner races, we decided to use the oil bath once again.

Erle and Andrew carried the oil bath and propane gas cylinder to the C2 shed and set the burner going under the oil bath. Everyone wore goggles and gauntlets in case of hot oil splashes, and a suitable fire extinguisher was at hand just in case. The big end bearing inner races were gently heated in the oil until it was up to temperature (it takes a long time to warm up while you are waiting!). With Andrew controlling the gas supply, Dave lifted the basket from the oil bath and Erle picked them out and slid them on to the crank pins, not forgetting the spacer rings between the two races on each crank pin. It only takes seconds for the bearing races to lose their heat and to shrink on to the crank pins.

While we had the oil bath in the C2 shed, Dave suggested using it to fit the expansion link pivot sleeves onto the trunnions. Maybe we didn't leave the sleeves in the oil bath long enough, or maybe the interference fit was too heavy, but the first sleeve got stuck half way down the trunnion, and the others didn't fit at all. This was not an insurmountable problem though, as Andrew took the expansion link covers and pivot sleeves to the hydraulic press and pressed all the sleeves into place.

Chris's wife Jan works for the Parks and Gardens department, maintaining all the beautiful flower beds which adorn most of the Ffestiniog Railway stations. While Jan was working in the morning Chris looked after their dog, while Jan did the dog sitting in the afternoon allowing Chris to join us with work on the C2.

Dave asked Chris to determine the relative lateral positions of the reverser weighshaft cranks and the expansion link bearing brackets on the motion brackets. This will allow us to determine the geometry of the reverser weighshaft crank pins (Dave has made these before, but got the geometry wrong. We'll do it correctly this time!). Chris found a way of obtaining the relevant dimensions, and documented them so that Dave can finalise the design of the reverser weighshaft crank pins as a homework project.

Next on Chris's list of tasks was to ream out the lifting link pin collars. The existing collars are a very neat design with a flange to protect the lifting link ball bearings, but are a very sloppy fit on the pins. We will make new lifting link pins, so there is an opportunity to make the pins a little larger so that the collars are a good fit. Chris used a 3/4" reamer in a lathe to neaten up the bores of the collars. Wire wheeling the collars removed remnants of paint and corrosion, allowing Chris to prime them and then put on an undercoat of paint the following day.

Dave was unsure if the valve gland oil pots and ports had been cleaned, so Chris inspected them. It appeared as though the oil pots had been cleaned previously, but the oil ports still contained a little contamination. Chris therefore ensured all oil ways were clean.

Jack joined us on Sunday, and was tasked with making a new piston rod gland. One of the originals is reusable, but one was broken. A drawing and a billet of bronze was available, along with the gland housing which the gland has to push into. Jack did a superb job of making the new gland, including making it a press fit into the housing. He then finished the job by using the hydraulic press to press the gland in. We'll try and twist jack's arm to join us at future C2 working parties, as he's a very competent machinist.

With the roller bearings fitted to the big end bearings, Erle and Dave were able to mount the connecting rods on the driving crank pins. Since Andrew had finished machining the crosshead bottom slippers, the crossheads could be clamped onto the slidebars, and the little ends of the connecting rods supported by the gudgeon pins which Andrew had previously made. With the connecting rods in approximately the correct place, the engine starts to look a lot more complete!

Supported this way, the vertical alignment of the connecting rods is slightly incorrect, since the little end bearings are absent. However, the lateral alignment can be determined, which is what we were after. There is very little radial or conical play in a cylindrical roller bearing, so the amount of lateral play in the connecting rod is only about 4mm over their length (five feet). Erle and Dave took measurements of the lateral positions of the big and little end bearings relative to the driving cranks and crossheads respectively, with the aim of determining the big end bearing cover plate and little end bearing thicknesses. The 4mm play can be dealt with by taking measurements at both ends of the range of play, and then using an average value for the nominal position.

Because the big end bearing cover plates were not present, Erle aligned the big end bearings by placing a straight edge across the inner and outer bearing races. This allowed him and Dave to measure the lateral position of the connecting rod little end relative to the crosshead. Alternatively, the little end could be mounted centrally within the crosshead, and measurements taken of the position of the big end relative to the driving crank pin. Either method seemed to show that the connecting rods don't align well between the crossheads and driving cranks. This could be due to the connecting rods not being perfectly straight, or could be due to the driving wheelset being misaligned in the horns (it appeared centralised, but it's difficult to measure accurately). We should be able to correct this by bending the connecting rods ever so slightly (just a few millimetres over the five foot length of each rod), but before doing so Dave would like to move the locomotive onto a different section of track to check if the wheelset alignment is affecting our measurements.

Erle, Chris and Jack headed home on Sunday evening, but Andrew and Dave stayed to continue work on Monday. What had not been anticipated was that there was an all-day power outage at Boston Lodge on Monday while the local electricity board replaced a supply pole which had been attacked by woodpeckers (only in rural Wales!). This meant that we could not use any power tools, and only natural light was available.

The next step towards completion of the crossheads will be to finish machine the top slippers. These need to be a precise distance from the bottom slippers to form a close fit around the slidebars. Thanks to Andrew taking a skim of the top slippers after whitemetalling, we had two flat surfaces which could be measured. Andrew and Dave therefore took a set of measurements of the gap between top (unfinished) and bottom (finished) slippers to determine how much material remains to be removed from the top slippers. This is not simple, as the two faces are not currently parallel (they need to be), so measurements were taken at each of the four corners of each crosshead. We can use this information to determine how much packing to place under the top slippers when they are machined, to result in them being parallel with the bottom slippers when finished.

Shortly after completing the above task, Andrew received a telephone call from Erle. Erle had gone home and immediately started drawing up the connecting rods, crossheads, slidebars and driving crank pins. However, he had spotted a couple of dimensions which he hadn't recorded. One of them was easy to supply, as Andrew had taken measurements of the crossheads previously, and we could send Erle a copy of the relevant page from our log books. The second set of dimensions required some additional measurements, but since we had the measuring equipment already to hand, this was easily accomplished.

As daylight started to fade, it became impossible to continue working, so Andrew and Dave joined the Works' staff for a pint in Spooner's on the other side of the Cob (which was not affected by the power outage); a thoroughly pleasant way to finish off a slightly strange day at Boston Lodge.

With it being a four-day working party, and having five people working on the C2, this one felt like the busy working parties of pre-COVID days. A great deal was achieved, both in terms of components being machined and measurements taken. All very satisfying!

Update: Between Christmas and New Year, Andrew was able to find some extra time to be at Boston Lodge. The expansion link carrier pivot sleeves on during the December working party (see above). One of the sleeves was deliberately left oversize as it would require later machining. Andrew decided to tackle this job by mounting it on one of the lathes in the machine shop.

This turned out (no pun intended) to be quite difficult as the piece is not well supported as can be seen from the photographs. The tool therefore chattered quite badly on the first cut leaving a very poor surface finish. The solution was to use a centre in the tail stock to hold it more firmly but without flexing the work piece too much. Unfortunately, because the carrier had been s badly made in China, the centre hold on the end of the pivot was no in the centre. So this required welding up and a new centre drilling in the end of the pivot. Andrew only managed to break one centre drill trying to drill out the weld! But this had the desired effect and it was possible then to turn the pivot to the exact dimensions while achieving a very good surface finish. A worth while day spent in the machine shop.