Much thought was given to the design of the rings and what information was available was studied. There appears to be surprisingly little on PTFE piston rings published so I was working in the dark to some extent. Obviously a gap of sorts would be necessary to cater for the high expansion of the PTFE and there seemed to be various ways of doing this. One way is to turn the ring to size and then cut it through at 45° so that the joint overlaps. Another is to make an overlapping stepped joint but this seemed a bit fiddly to make.
In the end I decided to use two thin rings side by side with a simple vertical gap in each. The gaps would be placed at 180° to each other so that leakage through the gaps would be negligible.
The rings were simply turned from some 1 inch diameter PTFE rod. The inside of the rod was drilled and bored out to a diameter 0.015" larger than the diameter of the bottom of the groove in the piston and the outside of the bar turned to a diameter 0.01" greater than the bore of the cylinder so that the rings would be slightly oversize. The rings were then parted off to a thickness such that when two of them were side by side in the piston groove, there was a 0.005" side clearance in the groove. The rings were then cut with a sharp knife and a section removed so that when the rings were fitted in the cylinder bore, the ring gap was 0.01". These clearances (to allow for expansion) were all 'guesstimates' and only a trial run will show if they are enough to prevent the rings seizing.
Turning the PTFE bar to size for the rings
The finished rings
Rings fitted with staggered gaps to prevent leakage
The cylinders could now be rebuilt and fitted to the frames but first I had to make the new steam connections and turn up the aluminium covers for the cylinder and valve chest end covers.
The aluminium covers were fairly simple, although fiddly, turning jobs from bar. The sides and ends of the covers are only 0.02" thick so a bit of care was needed not to damage them by taking over enthusiastic cuts! The really fiddly ones were the ones that go on the rear cylinder covers as they have to be bored out to fit over the cylinder cover boss and also have recesses filed in them to clear the slide bars. By the time I had done this there was not a lot of cover left! Both valve chest covers and the rear cylinder cover are a push fit and should hold themselves in place (if not, a bit of Loctite will secure them!). The front cylinder covers are held on by a central nut on a stud tapped into the main end cover.
Next job was to alter the steam pipes from the mainfold to the outside cylinders to threaded connections. To avoid making a new manifold I tapped the ends 3/8" x 40 ME and turned up some new stubs to connect to the cylinders. These are threaded 3/8" x 40 at the manifold end and 1/4" x 40 at the cylinder end as were the originals. To assemble the pipes and manifold, the stubs are screwed right into the manifold, the manifold fitted between the frames, and then the stubs are unscrewed until they reach the cylinders when the ends are screwed into the cylinder inlet blocks. The idea is pretty much the same as used on many loco designs. To lock the stubs in place and stop them working loose in use, I also fitted some thin 3/8" x 40 nuts on the manifold end of the stubs. The photo below shows the fitted assembly. The threads were liberally coated with the Rocol OilSeal before assembly to hopefully seal them. The original PTFE 'olive' on the connection to the middle cylinder was changed to a copper one at the same time, better to withstand the heat.
New steam pipes threaded into the manifold
The above photo was taken after a test run, hence the 'cooked' appearance of the sealant! Also visible in the top left of the photo is a little brass oil tank which feeds oil to the middle crosshead and slide bars via a 1/16" copper pipe. This is accessable by removing the front cover between the frames and can be filled up before a run.
Before refitting the lubricator (I decided to stick with the original for the time being) I changed the return springs on the pump rams to slightly softer ones as the originals were quite stiff and the lubricator needed quite a bit of effort to drive it. I also shortened the rams by about 1/32" in an effort to reduce the output which had still proved to be excessive at the last run before stripdown.
After refitting all the valve gear etc I gave the completed chassis a run on air and it ran very nicely and smoothly on about 10psi. The exhaust beats still sounded pretty even so I chose not to try retiming the valve gear.The valves hadn't been moved on the valve spindles so the timing shouldn't have altered anyway.
At this point I decided to hurriedly put the rest of the loco back together for a trial run and took Helen to the 2½" gauge invitation day at the club on May 17th. I really wanted to test the chassis before going any further with the painting in case anything needed attention. I was also getting withdrawal symptoms as I hadn't driven her for so long!
The run proved to be a fairly short one as after the first lap it became apparent that the lubricator was supplying little, if any, oil to the cylinders and the loco was very 'tight'. I did another couple of laps to see if things would improve but they didn't so I gave up for the day rather than risk any damage to the valves etc.
The next day I looked at the lubricator and the problem was immediately apparent - the new springs I had fitted were too short and the rams were not returning to the top of the stroke which meant they were not uncovering the inlet ports and allowing oil into the bores. This was soon sorted by fitting longer springs and we had another test run the following Sunday. The weather was absolutely awful with heavy rain but I managed about 8 laps before I called it a day. Helen seemed to run very well and seemed to coast with the regulator shut much better than before and I put this down to the new PTFE rings with their reduced friction. There was no sign of any leakage past the pistons and no tightness so it looks as though the rings are a success. Time will tell though!
Now I was happy that the chassis was running ok it was time to make a start on painting the boiler. The first job was to correct a small fault on the cleading. It didn't fit as well as I would have liked around the joint with the smokebox and when the boiler band was fitted, the band was slightly proud of the smokebox barrel at the top, rather than slightly below. In the end I realised that the problem was due to the boiler lagging being too thick on the top of the barrel and the only way to cure it was to remove the cleading and reduce the thickness of the lagging. This was eventually accomplished after a bit of a struggle as the cleading had stuck to the cork lagging and removing it damaged some of the lagging! The damaged bits were easily replaced though and when the cleading was refitted, the job looked much better.
I decided to paint the smokebox first but had one small job to do before this and that was to fit some handrail knobs on the sides. The holes for these were marked out and drilled taking care to ensure that the rails would be horizontal when fitted. The rear holes were tapped so that the knobs screwed straight in as it would be very difficult to get at nuts on the inside but the front ones were easy to get at so these were drilled a clearance size.
The smokebox, saddle and boiler cleading were rubbed down with 1500 grade carborundum paper to give a good surface for the etch primer which was sprayed on using the aerosol can to save having to mix paint and use the airbrush. The aresol works fine so long as you are careful not to get too much paint on - it goes on much thicker than when using the airbrush but it's a lot more convenient to use!
The primer was left to dry for 24 hours and then gently rubbed down with 1500 grade paper again. The primer drys quite hard and will stand careful rubbing down. This leaves a nice velvety surface ready to take the top coat. Incidentally, I also primed the backhead and the bodies of the valves and fittings which had been left in place. I intended to paint the backhead satin black and the fittings red which should look very smart! I think a painted backhead looks so much better than one left as bare copper showing all the solder runs etc!
The boiler cleading was masked off to leave the smokebox ready for painting and this was then sprayed with the Halfords high temperature gloss thinned with 25% thinners and using the airbrush. I put on two good thick coats allowing the recommended drying time between coats and the finish was quite pleasing - to me anyway! The gloss is not too 'shiny' and looks the part. Whether it will dull down a little with the heat remains to be seen.
Next the backhead was hand painted with two coats of the Halfords satin black and the fittings with the high temperature red gloss.
Next was the barrel and this was where it would probably all go horribly wrong! The smokebox and backhead were masked off with masking tape and thick paper and then the barrel was sprayed with the Precision Paints olive green thinned with about 20% quick drying thinners and sprayed at 25psi. Looking back, I should have made a rotating jig to hold the boiler which would have painting much easier. It's difficult to spray, hold the boiler, and turn it to get at all the bits!
Frankly, the first coat looked pretty awful - very orange peely. Bugger! Taking the bull by the horns, I decided to try a method suggested by Chris Vine in his book. I quickly thinned the remaining paint down even more and then sprayed on 3 more coats in quick succession as thickly as I dare. This built up one very thick coat which was then allowed to dry as slowly as possible. It worked a treat and the paint pulled out to a very nice glossy finish with no sign of orange peel. The finish was not perfectly flat but looked great and I was more than satisfied with it. There were a couple of small 'blobs' on the barrel but it may be possible to carefully sand these off when the paint is fully hardened. Then again, they are not too obtrusive so I may just leave them!
Flushed with the success of this painting method I applied it to painting the running boards and the smokebox door with the HT gloss black with equally good results.
The National Rally at Rugby was fast approaching so, once again, I hurriedly put Helen back together so she could be run. It would have been nice to have had everything painted but it wasn't possible in the time available. I did however carry out some finishing work on the tanks and rear bunker before I refitted them. The front corners of the side tanks were rounded off which looked much better and some 1/16" half round brass beading soldered along the top edge of the tanks. This also made a big improvement to the looks.The beading could have done with being slightly wider so it overhung the sides a little more but by making the inside edge of the bead flush with the inside of the tank side, it looks ok.
The rear corners of the bunker were also rounded off but I didn't have time to fit any beading to the top edges.
The whole lot was literally slung back together the day before the rally and off we went to Rugby.
It was a gorgeous sunny day and Helen ran like a sewing machine on the first run and we did about 3.5 miles, only stopping for coal and water. Rugby is a superb track, smooth as a billiard table, and, surprisingly, no expansion gaps in the rails. I found that after the initial climb out of the steaming bays, I could run with the valve gear well notched up and the regulator just cracked open. The exhaust was just a gentle purr. This was probably the best run we have had to date. I think the PTFE rings have made a big difference to the free running of the loco and they seem to seal perfectly.
I eventually came off after about an hour after I let the fire go out whilst faffing about topping up the lubricator!
When in the steaming bays I was approached by Simon Clough and Ron Warren and asked if they could have a look at Helens grate and ashpan. Ron has an original Helen Long that he built 30 years ago but had not got to run properly yet. He and Simon had been experimenting with gas firing his Helen but this had proved unsuccessful and he wanted to fit a grate and change to coal firing (quite rightly so!)
We managed to turn Helen on her side so that Simon could get some photos and get a good look at my grate design but this treatment obviously gave Helen the sulks as my later attempt at a second run was a dismal failure. She just would not run at all well and really struggled to get around and felt very tight. I suspected lubricator problems again but on coming off I noticed that the front bogie bearings were 'squeaking'. I reckon they had run dry and were causing the tightness and the reluctance to run. A quick squirt of oil soon sorted that out but it was getting late so we called it a day and packed away. Still, Helen had put up an excellent performance and it had been a good day.
So. it's back to the painting again with just the tanks and the lining to do now. The following photos were taken after the Rugby rally and the tanks had been removed. There's one or two scuff marks on the paintwork where the tanks sit and a few dings around the firehole door caused by the shovel!
Rear view of chassis with the backhead
3/4 front view of smokebox and boiler
Side view of front end showing ally covers on the cylinders
Although I was a bit 'iffy' about the colour to begin with, it's really grown on me and I think she'll look ansolutely stunning when the painting is finished.
Work has been a bit slow over the last few weeks but I've been adding a few details to the tanks and the cab before the final painting. The beading has been added to the top edges of the rear bunker, around the door openings in the cab, and on the top edges of the cab roof. I've made the four window frames for the side windows using a jig to make them easier to form. The jig was just four lengths of steel dowel pushed into holes in a wooden block. I found it easier to bend the beading after it had been annealed. The problem is if you bend it in the 'hard' state it tends to twist as you bend it and is difficult to keep flat. The join in the frames were silver soldered to stop it coming apart when the frames are finally soft soldered to the cab openings. I made the frames slightly smaller than the window openings to leave a small lip so that I can glue in a suitable piece of plastic sheet for the actual windows.
Cab window frames with jig used to bend then
I've still got the two to make for the windows in the spectacle plate which are a more awkward shape.
Inbetween this I've been to two more rallies, one at South Cheshire MES and the other at Stafford.
The one at South Cheshire was a bit of a disaster as Helen came off the rails twice at the same spot and I can only conclude that there was something about the track at that particular point that Helen didn't like! Unfortunately she suffered a bit of damage. The paint on the wheel rims got badly scraped and six of the axlebox spring pins got well and truly bent. I replaced the spring pins rather than try and straighten them (they only screw in) and just touched up the paint on the rims for the time being. The rims really want sanding down again and repainting from scratch but I'll do that later. It will no doubt happen again anyway!
Stafford was a more successful day thank goodness and we had a good run until the heavens opened at about 2pm! (typical Stafford rally weather!). I struggled at first to maintain pressure until I tried using the blower on the run as well. The Stafford track is an oval with one side uphill and the other side downhill. I was initially loosing pressure when coasting down the hill and then running out of steam halfway up the hill on the other side. Using the blower on the downhill bit solved that problem and we had no further trouble getting around.
I have noticed that towards the end of a long run, Helen seems to be getting a bit stiff and I am not happy that the lubricator is supplying enough oil. There is only a slight 'greasyness' inside the chimney after a run and no visible oil around the top.
I decided to investigate this after the Stafford run and so removed the boiler again to get at the lubricator. I noticed that the roller clutch in the drive arm seemed a very sloppy fit on the drive shaft and could tilt sideways. It drove fine when the arm was at right angles to the shaft but slipped a bit if the arm was tilted. This may have been part of the problem. I have since checked up and it is possible to get these 1/8" bore roller clutches with a thin plain bearing at each end which will hold the clutch in line with the shaft and stop it tilting. I haven't found a supplier for these yet but probably a bearing stockist would be able to get them for you.
As a 'temporary' cure I put a washer either side of the clutch which allowed just enough clearance for the drive arm to rotate freely on the shaft but stopped it tilting on the shaft.
While I'd got the lubricator off again I decided to try and increase the capacity of the oil tank to give a longer run between fills. This is not easy to do as there is very little space where the lubricator fits but I eventually managed it by soldering a length of 5/8" copper tube with an end cap into a hole in the side of the original tank. Not very elegant perhaps but it's probably doubled the capacity of the tank!
Some time ago I had shortened the rams in the oil pumps to try and reduce the output but the lubricator has never seemed to work very well since. I've now made some new rams the same length as the originals and fitted those which should restore the output. It will probably be too great now so I've fitted a needle valve to the output of the lubricator which can be adjusted to allow some of the oil delivered to bleed back into the tank. In theory it should now be possible to regulate the output by altering the needle valve, just as you alter the output from the axle pumps using the bypass valve. Whether it will work remains to be seen! It will probably be all or nothing! Still, it's better to have too much oil than not enough, especially with piston valves.
Lubricator showing the tank extension and the needle valve
I've also decided to alter the way of filling the tank as the pipe filler is a pain in the bottom and you can't see inside the tank to see how much oil is in it. I've retained the original lid but fitted a hinged flap to the top instead which allows access to the needle valve and makes for easier filling (hopefully!)
I also noticed that one of the steam pipes has been leaking (again!) where it screws into the cylinder. These steam pipes are becoming a real pain! I've looked around for a higher temperature sealer and come up with Loctite 5920 (available from Halfords) which is actually a high temperature (up to 350° C) silicon gasket cement. I'm going to give that a try this time and plaster the stuff everywhere! If that doesn't stand the temperature I don't think anything will!
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