12/1/2012

Wow, yet another year gone by!

Before taking the boiler to the club for our boiler inspector to give it the once over, I decided to fit another cross stay over the top of the firebox to be on the safe side. This was made in the same way as the originals - a length of bronze bar threaded at each end and a double threaded nipple screwed into the firebox wrapper and then caulked. I did look at putting another set of stays towards the bottom of the firebox, below the tubes, but didn't in the end as they would be too close to the foundation ring to make a great deal of difference.

I took the boiler to the club along with my hydraulic test rig and had a chat to the boiler inspector. He agreed with my suggestion of dropping the working pressure to 70psi and we also agreed to reduce the period between hydraulic tests from 4 years down to 2 because of the age and construction of the boiler. We therefore gave it a test to 140psi which it passed with no problem.

With the boiler sorted it was now time to tackle the cylinders and motion work.

First job was to remachine the cylinder port faces. This was done by mounting the cylinders in the lathe and skimming the faces with a fly cutter. I think it's easier to get a good finish with a fly cutter than using an endmill.

Skimming the port faces with a fly cutter

The edges of some of the ports were a bit rough so I trued these up as best I could with a 2mm carbide endmill in the small mill which is ideal for little jobs like these that don't demand heavy cuts. As it happens, I only needed to take a few thou off to get a good clean edge to the steam ports. The exhaust ports were not so good but that doesn't matter really as they don't serve any purpose in the valve timing and are just a hole for the exhaust steam to escape through!

Truing the ports

The valves were tackled next and I thought I would have problems with them matching the now slightly oversize steam ports. One proved to be just wide enough to fit the ports but the other was too narrow and needed a thin strip of brass silver soldering onto one edge and then machining down to the correct length. Both of the exhaust cavities were considerably narrower than they should have been and just needed widening. This meant that the valves would have originally had exhaust lap (the cavity was narrower than the distance between the ports) which would have made the ports open to exhaust very late and wouldn't have helped the free running of the loco (assuming it ever did run).

The cylinders could now be fitted to the frames again along with the valve chests and the steam and exhaust pipes. The original graphite packing on the pistons was a bit loose in the bores so this was replaced with some square section PTFE packing which I haven't tried before. It will be interesting to see how it performs. The cylinder covers etc. were all fitted with new gaskets. One thing I noticed when reassembling the cylinders was that a lot of the screw threads are 1/8" Whitworth which dates the loco a bit. Later models would have used 5BA.

The original drive to the valves should have been the usual threaded brass square nut fitting a slot in the top of the valve with valve adjustment made by screwing the nut along the threaded valve spindle. Usually you can do this by disconnecting the combination lever from the valve crosshead and then rotating the valve spindle but on this loco the valve crossheads are square and run in proper guides on the end of the steam chest. That means that you cannot turn the valve spindles to adjust the valve and you would have to remove the valve chest from the cylinder, rotate the nut around the valve spindle, and then refit the valve chest and try again. What a pain! What the builder had done was to dispense with the thread in the nut and just have a plain hole. He had then put a sawcut across the end of the nut through to the other side of the hole and drilled and tapped for a clamping bolt.

Original valve spindle and nut

The valve spindle was actually threaded as per the drawings so perhaps the builder had a go with the original idea and then changed it? In any case, the nuts on these valves are much longer than those shown on the drawings and still couldn't be rotated even if you took the valve chests off! That's perhaps the real reason behind the design change.

Anyway, the nuts were a sloppy fit on the spindles and in the valves so I decided to make new ones. The slots in the valves were not very square so these were milled out to take 5/16" square brass, a bit bigger than the originals. I wasn't very keen on the split clamp idea, especially on the threaded bit of the old rods, so I made new rods which were plain all along and fitted the new nuts with two stainless grub screws which locked down onto flats milled onto the valve spindles. I'm not 100% happy with this idea but I think it will be better than the originals.

New valve nuts with grub screw locking

Time now to reassemble all the motion work which was not without problems. The steel motion work had been given a coat of varnish or something similar at some time and the steel had started to rust in places underneath. The 'varnish' was stripped off by soaking in thinners so that the steel could be cleaned up again before refitting.

I had problems with the slide bars when I tried to refit them as they were miles out of line with the crossheads! I had to machine some of the ends that fitted to the cylinder end covers and the motion brackets to get them to line up properly and fit shims to the others. I began to think that I hadn't put the cylinders back correctly but the slidebars must have been a poor fit to begin with. One crosshead looked as though it had only been touching the slidebars at two corners. There were one or two tight spots in the valve gear after fitting which were traced to a lack of clearance between the front of the combination levers and the slots in the valve crossheads. Just needed the slots extending a bit with a file.

After roughly setting the valves I gave the chassis a run on air. It ran very well on about 10psi and things were looking good. There was a bit of a knock coming from somewhere though and using a bit of plastic tubing as a stethoscope I traced it to the centre axle. I did notice that the left hand expansion link didn't seem to be moving as far as the right hand one and it's motion seemed a bit jerky, so I took the chassis back into the house to investigate. Waggling things about showed that the left hand return crank was loose on the crankpin and could be moved quite a bit. I thought the taper pin holding it had come loose at first but it proved much worse than that. The crankpin was loose in the wheel! Oh @?%$! It wasn't loose enough to rotate completely but just moved a few degrees one way or the other. Aahh! Why do I take on these jobs? I must be mad.

There was nothing for it really but to take the wheel set out of the frames which meant dismantling half the motion again. Also, the axle pumps are driven off this axle so the ecentric straps had to come off as well, plus half the brake rigging.

I've managed to get the wheels out and it appears the crankpins are fitted through the wheel boss and then rivetted over on the inside. Funny enough, this loose crankpin looks as though someone has tried to tighten it up as the end is not as nicely rivetted as all the others and the paint is chipped off. It seems that this may not be a new problem.

If the crankpin was just a press fit, it would be easy to take it out and Loctite it back in but it makes it difficult with the end being rivetted over. Getting it out will be difficult unless I press the wheel off the axle which I want to avoid if possible. One alternative is to tighten it up by peening over the end again and drill for a pin through the wheel boss into the crankpin to make sure it can't rotate again. Another problem is that the end of the crankpin is drilled to take the pin that locates the return crank so the crankpin's got to be set in the correct position. Problems, problems, problems! (as Marillion said)

18/01/2012

After sleeping on the crankpin problem I decided to try grinding off the rivetted end of the crankpin so that I could hopefully get it out. This proved fairly easy with a carbide burr in the dremel and I managed to get the crankpin out without damage. Fortunately, the hole in the wheel boss had not been countersinked and the end rivetted into that, otherwise I don't think I could have removed it so easily. This now gave me the opportunity to use Loctite to secure the pin into the wheel, so that just left the problem of locating the crankpin at the right position in the wheel. I decided the easiest way was to use the lathe as a jig. The wheels were located in the gap between the sides of the lathe bed and the good crankpin rested on a block of metal so that the line between the crankpin and the axle centre was more or less horizontal (the return cranks and the eccentric rod drive bolts had been refitted to the crankpins before this). Suitable spacers were placed on the lathe cross-slide and a drill shank chosen to fit the gap between the spacers and the bolt on the return crank. If the wheel was now reversed, the loose crankpin could be rested on the spacers and the drill shank to set it in the same position as the fixed one. The loose crankpin could then be Loctited into the wheel and set in the right position.

I decided to pin both crankpins as well to ensure neither would move again. The wheel boss and crankpins were drilled to take a 1/16" silver steel pin which was also Loctited into place.

Drilling wheel boss and crankpin for pin

Once this was done I could refit the wheel and reassemble the motion. Another test on air was done which showed one of the valve settings to be very slightly out. This was adjusted and the chassis then ticked over nicely on 10psi of air at about 60% cut off. That's good enough for me!

Next job is to refit the boiler and try running it on steam.

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