HARRY’S GAME – YEO GETS NEW WHEELS
Fairbourne Railway engineer and EIM tech ed Harry describes the refitting of new wheel sets to one of the locos, plus a host of other challenges that arose...
Regular readers of this column will know that at the 12¼-inch gauge Fairbourne Railway we had to set up an urgent appeal after radial cracks were found in the wheels of our 6-inch scale Lynton and Barnstaple Manning Wardle 2-6-2T ‘Yeo’. The appeal proved highly successful (a huge thank you to those that donated) and with the imminent arrival of the new wheels from the Denver Light Railway workshops, there was a slew of other jobs to complete on the engine while it was out of traffic.
One of the major of these was to sort a replacement regulator valve, the other was a very annoying steam leak from the left-hand cylinder. The regulator valve proved relatively straightforward, as at some point in the past someone had fitted one of those nice, expensive fully serviceable stainless ball valves to it.
Unfortunately, however, these have quite a large body and the top of the J-pipe sits very close to the inner edge of the dome. Whoever had fitted it had decided to grind away a decent proportion of the nuts and the bracing that holds the valve together. It was this that finally allowed a bit of the seal to fail and leak through.
Cheaper better?
The solution to this was to fit one of the cheaper cast-bodied valves which have a significantly smaller body size.
The important thing with these is to fit them with the screwed-on face upwards, so that if the top seal should fail, the bottom seal along with the body of the valve will prevent any leakage.
The leak on the cylinder was far more problematic to deal with – the cylinders are an amalgamation of a cast cylinder bore and steel valve face with a joint that runs right through the middle of the exhaust pipework joint on the frame side of the cylinder. It is quite hard to explain but I hope the accompanying picture will show how it fits together.
The valve face is held down by
eight bolts that run across the engine and four that run along the edge closest to the frames. Across the outside edge of the cylinder it is held down by the valve chest cover studs which pass through the valve face, through the valve chest casting, then through the valve chest cover and finally are secured by a nut on top. This has to be wound down extremely tightly to get it to effectively compress the three gasket-jointed seals.
To get to this joint you need to remove the valve chest and to remove the valve chest you first need to disassemble the valve gear to remove the valve rod from the valve carrier. This proved an incredibly irritating task as the original builder split the valve gear to go both sides of the guide bars and then to be joined together by several pins and bolts. These have to be removed in a certain sequence otherwise the rods will wedge solidly against the motion bracket, the frames, the guide bars or at times all of the above...
Having removed the valve chest and the valve face, I discovered some of the issues – one of the studs had pulled most of the threads out of the cylinder block and two others were very close to doing the same. Combined with this several of the studs had started to show signs of failure on their top ends, where the nut sits.
This led to a decision to make all-new studs and to tap out one to a bigger size. Having assumed that a loco ordered for a railway in France would have been built with metric fasteners as much as possible it then took me a while to work out that the studs were actually 3/8-inch
Whitworth (BSW) threads. This actually worked out quite well as a handy next size up is M10.
The next challenge was going to be drilling out the pulled-through thread on the cylinder block – this is located under the side tank and it proved almost impossible to fit any of our portable drills in.
What I ended up doing was to make an adapter to fit my short-reach impact wrench and used that to drill out the hole to M10 tapping size. Some might say that it is not the best tool to use for drilling and they would be absolutely right – if I had more time, I would have borrowed a short-angled drill from one of the other railways, but unfortunately needs must when there is a deadline to meet so the impact wrench had to suffice.
After EIM editor Andrew Charman had made the new studs for me and I had cleaned out the tapped
3/8-BSW holes, all that remained was to clean off the mating surfaces of the joint, coat them with steam seal and put on a freshly annealed copper gasket, before reassembling the entire assembly only putting one of the rods in an awkward way round...
A question of size
This then left only the wheels to arrive and put in before the engine was ready for trials. Yet this too proved to be an interesting epic, as to make the most of the blanks of steel that were available the new wheels are slightly larger in diameter than the old ones. This required some interesting fitting work to be done on the brake hangers and specifically the brake blocks themselves to allow the wheels to go up into their final position.
This was mostly achieved by employing a grinder and a template to ensure a decent fit onto the curvature of the wheel as possible, while
maintaining as much of the brake block as possible too.
The other main fitting work was to set the side play on the axles, specifically the thickness of the bronze rubbing face that rubs against the wheel’s rubbing surface on the outside edge of the rim.
This was set by carefully lifting each wheel set into place using a trolley jack, then checking the fit, before dropping it down again, removing the axlebox, then using a sheet of Wet and Dry on the surface table, gradually taking down the thickness of the rubbing plate until they fitted beautifully. Due to the centre drivers being flangeless, I have set the boxes up to have minimal side play, with the intention that if we start to have issues, it is easier to take a little material off than shim it back out again.
One of the final hurdles to be overcome was found when we re-fitted the rods – the right-hand set fitted beautifully, the left-hand rear however had an internal rod eye diameter 4mm smaller than the rest.
I eventually traced this down to the fact that most of the old crank pins on the original wheel set still had the inner races of the roller bearings they were originally fitted with on them
– it was only the rear left which had lost the race at some point and someone had then machined the rod eye to fit the inner pin diameter. A quick trip to the milling machine to bore out the rod eye followed and this allowed the rods to fit nicely.
Take five
By this point it was about 9.30pm on a Thursday evening and we decided to call it a day before lowering the engine back onto its wheels. This was achieved with a much fresher head and body on Friday morning before the loco was pushed outside with some difficulty, filled up with water again and a fire lit in it for the first time in nearly four months. While the loco was coming round into steam I set to and set the valve events as I have described in a previous episode.
Once we had pressure on we came across another issue. I opened the regulator and the engine made a very short movement, then came to a standstill. This then happened again in the other direction.
There followed a reasonable amount of head scratching and pondering before I realised the return cranks had been fitted incorrectly, so one was leading the crank and one trailing the crank. This had the effect of putting steam into opposite ends of each side’s cylinder and locking it up at some points of travel.
Once this had been ascertained I
then spent a little while setting the return cranks to their correct position and also slightly increased the valve travel, to try and compensate for some of the lost motion due to the worn valve gear.
After resetting the valves I then took the loco on a few short trips up and down the station, stopping frequently to check for any warmrunning bearings. The rear right crank pin and the front left axlebox were ever so slightly off-cool but other than that everything seemed to be going well.
With a few laps around the station completed, I arranged with the controller to take the staff and ticket from the next train to arrive at Fairbourne station and to go for a slightly more extended run. This revealed that the left-hand side valve was over traveling and the right-hand side could do with a little tweaking. The bearings were running reasonably warm but not hot.
Following a weekend off, on the following Monday morning the return crank on the left-hand side was readjusted again and the valve position set, then the loco brought round into steam. Similar testing to Friday occurred with more and longer runs inbetween the service trains.
After the last service train of the day had returned, we took the loco up to the other end of the line at Penrhyn Point, hauling the water wagon to top up the water supply for the café. The only problem we encountered was the end cap falling off the left-hand-side return crank pin in the dunes above the tunnel. This cap is only held on by a pair of M5 grub screws so it will eventually be cross-drilled and a taper pin fitted.
Green light
Following this successful run, an early morning outing next day saw a fully-loaded test run to the Point before the first train, while the booked driver for the day prepared our Welsh Highland-style loco ‘Russell’ just in case we needed it. But after a very positive performance I passed Yeo out to enter traffic and it has performed extremely well since.
The increase in valve travel has helped the previously poor steaming and the steam leak on the cylinder is significantly improved too. However the loco now exhibits an impressive leak-past on the left-hand-side set of piston rings, that sounds like a mournful saxophone when steam is put on!
All the while that Yeo has been up on blocks the work of maintaining our operational fleet of locos has of course carried on. Russell was failed on a wash-out inspection with two bearings that were at the end of their lives and had caused the axle to turn inside the bearing housing, badly wearing the axle end.
This being the trailing bogie of the 2-6-4 it required the loco being lifted high enough to extract the wheelsets past the footwell and out into fresh air. They were then stripped down, the axle ends machined down, a sleeve press-fitted on and then re-building with new bearings. All of this was done while the diesel was running the service trains.
Not just locos
Of course the work is not only allocated to the motive power, our carriage fleet still requires attention. Our long-term rebuild project vehicle has nearly had its framing finished, with large sections of the hardwood frame replaced and we are now waiting on delivery of a plywood replacement called Medite which has come highly recommended by other railways. This product comes with a 50-year guarantee so hopefully will reduce the amount of work that is required to replace panels every year.
In between all of the other jobs that are ongoing, on our currently under overhaul bo-bo diesel ‘Tony’ the redesign of the gearbox tail bearing has been ongoing. Having discovered an unsupported, unlubricated, unsealed thrust bearing being sort of held in place by four bolts on the back of the automatic gearbox, I thought I should rectify the issue before it became a big problem.
A large lump of aluminium and a lot of phone calls to our bearing supplier later, a new bearing housing with a sealed 2-inch bore bearing in place was fitted and the propshaft re-fitted. The next job on this loco is sorting out the suspension to prevent the leaf springs falling out of the carriers when hitting a rough joint.
And finally, we have been operating an intensive, eight-train a day service for nearly six weeks now, and with Covid-19 still present and the Welsh Government instructions still in place we have been maintaining our cleaning schedule, so many thanks must go to our volunteers who have stepped up and made the effort to allow us to continue running – the small band of paid staff simply wouldn’t have the time to do all the cleaning without them.