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09/08/2008

Updates seem to be getting few and far between!

I've done some more painting and the tanks and rear bunker are now green as well! I was unsure as to what colour to paint the inside of the cab as photos of the cabs of full size southern locos seem hard to find. Gerald from the Association very kindly sent me a booklet about Stowe, the Schools class loco which did contain one photo of the cab interior. It appeared to be a sort of orange yellow so on another trip to Halfords I had a look at the car spray paint and found a colour, not quite the same but one I thought would do. The interior of the cab and the underside of the cab roof were then painted using this. While I was at it, I sprayed the outside of the cab roof with some of the Halfords satin black which looks quite nice.

Once again the loco was quickly assembled for another running day at the club (no wonder the painting is taking so long!) and I took a few photos before she got dirty again!

Still plenty to do but getting there slowly!

After giving her another run I noticed that she was still getting very stiff to move after a while and was not running well at all. I suspected that the modified lubricator was still not working properly and she was still short of oil.

Over the next couple of days I did some running at home on the rolling road to see if I could find the problem. Despite my earlier fears, the lubricator was actually pumping plenty of oil but she was still getting very stiff after only a short run and making a distinct 'squeaking noise' from the inside cylinder and the right hand cylinder. I started to suspect the valves and decided to take the centre one out and have a look. When it was taken out it was seen to be quite badly scored and had obviously been running very tight in the bore. When the right hand valve was removed it was in the same condition. This was obviously the problem. The valves, being directly exposed to the incoming steam, were getting hotter than the valve chest and expanding more, causing them to become very tight. What to do!

I decided to do what I had been thinking of for some time now and have another go with PTFE. There have been a few articles on making PTFE valves in Model Engineer over the years and they seem to have been used with some success.

It was obvious from my earlier experiments with the solid PEEK valves that this was not a satisfactory method of making the valves. The solid bobbins expand far too much and just seize solid unless they are made a loose fit when cold. They then leak until they get to working temperature. Other model engineers have had success fitting solid PTFE rings onto a metal bobbin, some fit split rings with an O ring underneath to help press the rings onto the inside of the valve bore. The idea is that as the PTFE ring expands with the heat, it makes a perfect steam tight seal against the bore but the natural low friction property of PTFE ensures that it will not seize solid. My concern was that Helens valves are much longer than normal types (due to the double porting) so the PTFE ring would have to be nearly half an inch long. Would the PTFE still seize in the bore as it expanded?

I eventually decided on a fairly simple way to do it which may or may not work. I decided to turn down the original stainless steel valves and fit a thin PTFE sleeve to the outside to form the actual valve head.

I didn't have much time to do this as the Rally at Sutton Coldfield MES was only a couple of days away!

I decided to have a go with the middle cylinder valve first to see if my idea would work or not. This cylinder runs hotter than the two outside ones so would be a good test.

Each head of the valve was turned down in the middle, just leaving a thin flange at each end to retain the PTFE sleeve, bit like a cotton reel. The sleeves were then turned from 1/2" solid PTFE bar. The bar was drilled so that the centre hole was 0.01" larger in diameter than the reduced diameter of the valve head and then the outside diameter turned down until it was very slightly larger than the inside diameter of the valve bore. The idea is that the finished sleeve can just be pushed into the valve bore by hand and the clearance between the inside of the sleeve and the bobbin gives the PTFE somewhere to go when it expands! The sleeves were then parted off and carefully faced to length (by pushing them onto a suitable mandrel) so that they would just fit between the end flanges of the valve heads. For good measure I turned a few shallow oil grooves in each sleeve to help the lubrication. The sleeves were then slit lengthways with a sharp knife so that they could be opened out and fitted onto the valve heads.

This will not be ideal as the thin flanges left on the ends of the valve heads will not seal against the bore and the valve timing will be controlled by the PTFE sleeve which will actually be too short to give the correct valve events. It'll be close enough to prove whether the valves will work or not though!

Original stainless valve bobbin fitted with PTFE sleeves

The modified valve was liberally coated with steam oil and fitted back into the cylinder. It was a bit of a struggle as the sleeves were quite a tight fit. I had made a note of the position of the valve on the valve spindle before I removed the valve so that I would not have to redo the timing!.

Back to the rolling road and a quick steam test. Despite my fears, the valve didn't seize at all although you could tell it got a little tight when very hot. So far so good! Another major concern had been that as the sleeves had to be split to fit them,the ends of the thin sleeve may spring out and jam in the ports. This didn't happen either.

Encouraged by the results so far, I modified the other two valves as well. Another steam test on the rolling road and what a difference! No signs of any seizing, no leakage of steam past the valves at all, and the exhaust was really sharp and crisp. She sounded like a completely different loco and would actually run in mid gear with the regulator only just cracked open. I couldn't believe the difference!

The next day was the rally at Sutton Coldfield and that would be the real test! If the new valves proved to be ok then I will make some new ones from scratch to allow the PTFE sleeves to be the full width of the valve head and let the sleeves control the valve timing, rather than the thin flanges at each end.

When we got to the rally at Little Hay, I deliberately waited until later in the day before running Helen as I was a bit apprehensive about the valves and didn't want to hold everyone else up if I had problems. Also, last year I had a lot of trouble with the front bogie here and it kept derailing all the time which was another cause for concern.

Both fears were unfounded and Helen ran extremely well for over an hour just purring around on very little regulator. The main problem was the track. It's aluminium and previous runners had given it a liberal coating of oil! It was very greasy and I had great difficulty getting any grip. It was a case of running notched up to reduce the power and gingerly opening the regulator. Even then the wheels spun like crazy when starting off. Once we were going it was not too bad but with Little Hay being such a short track, we had to keep stopping at signals to let drivers in front get away. Towards the end of the day, I had the track to myself and got some good continuous laps in. I then let brother Mick have a drive and from a distance Helen sounded really nice, the exhaust being very crisp and distinct.

Overall I was very pleased with the run, so much so that I rang up the organiser of the LBSC Memorial Trophy competition which is being held at Little Hay on September 7th and entered! Not sure what I'm letting myself (and Helen) in for but it's not a serious competition, more a bit of fun to celebrate the designs of old Curly. Still, it will be an incentive to get the painting finished!

As the PTFE valves seem to work ok, I've now made up a new set with the correct length sleeves and fitted them.

I'd run out of 1/2" stainless bar so used gunmetal for the new bobbins instead. I only just had enough PTFE left as well!

I started off by parting off 3 lengths of the gunmetal bar, facing both ends and then drilling through a good clearance fit for the brass carrier. I then turned up a steel mandrel held in the 3 jaw so that each bobbin could be mounted on this and turned to final shape and size. The heads were then turned using a sharp parting tooltaking care to get all the dimensions correct for the grooves for the PTFE sleeves. The thin flanges at each end of the valve heads are 0.012" thick so are a bit fragile! I had to keep the overall length of the new valves as short as possible because of end clearances in the valve chest.

Turning the new valve bobbins with a parting tool

Once the bobbins were shaped, they were faced off to the correct length. The PTFE sleeves were made as before, but this time they were sligthly longer of course.

Completed bobbin with one sleeve yet to be fitted

When all three valves were refitted, I took the opportunity to check the valve timing. It was slightly out so a small adjustment was made. I set the valves with compressed air, using a length of rubber pipe held to the ear and held over the end of the drain cocks. You can hear when the valve opens and air enters the cylinder. I just adjust the valve until the air can be heard escaping from the drain cocks at the same position of the piston for each end of the cylinder. If you do this with the reverser set to full valve travel, the valves open just before top dead centre on each stroke.

One thing I noticed when timing the middle valve that there was quite a bit of lost motion in the valve spindle. Looking at the drive, it appears that the PEEK bush for the main 2 to 1 lever has developed quite a bit of play and the lever pivot is tilting slightly in the bush resulting in the lost motion. I think the problems with the valves have put a lot of strain on the bush and it's deformed rather than worn. When I get chance, I'll replace it with a bronze bush instead. Unfortunately I can't get at it without removing the boiler again so it will have to wait until I have to do that.

Another quick steam test showed everything to be ok except that she would not notch up quite so well. I think this is due to the middle valve not getting it's full travel due to the worn bush.When notched up in mid gear, the valves only just open, basically they are just opening by the amount of lead designed into the valve gear which is only a few thou. I think the middle valve was probably not opening at all when notched right up and the two outside cylinders are doing all the work. I think this effect has become more pronounced now the correct length PTFE sleeves have been fitted. Before, the shorter sleeves would allow the steam to be admitted slightly early, compensating for the lost motion. Anyway, I'm off to the club tomorrow to give Helen a proper run to see how she performs now.

10/08/2008

Went to the club today and had a pretty good run round. There was only Mick and I there today so we had the track to ourselves. Mick's Rob Roy is running well now he's 'tweaked' the valve gear and he went round like the proverbial bat out of hell!

Helen ran well after a false start. I hadn't got the fire burning properly at the front of the firebox when I first lit up and only managed a couple of laps before running out of steam. I eventually dropped the fire and started again and had no further problems.

The new valves seem to working well but the lost motion in the middle valve is noticeable when the gear is notched up. As the gear is notched up you reach a point where she starts to run very rough and I think this is when the middle valve stops opening and the middle cylinder ceases to do anything. I might try and get the bush replaced this week after all as I will probably have another run next Sunday.

Helen's steam certificate expired today so I've arranged a steam test with our club boiler inspector for next Sunday.

16/08/08

For anyone interested there is a short video here of Helen running at Little Hay at the rally on August 3rd. Click on the floppy disc symbol to download it. Caution - it's a big file and takes a few minutes even with broadband!

18/08/08

I decided to go ahead and renew the pivot bush for the 2 to 1 lever now rather than later which meant taking the boiler off again. Mind you, I've done it so often now that I can do it in my sleep! The bearing bracket was removed and the PEEK bush replaced with one made from aluminium bronze, making sure the bore was a good fit for the lever pivot. The boiler and tanks were then quickly refitted and the loco given a quick steam test. All was well and the loco would run in nearly mid gear again now that the full travel for the centre valve has been restored.

Yesterday, I took Helen to the club for the official steam test which she passed with no problems so we are all set for another years running. As she was in steam I gave her a run round the track and finished up staying on for over 4 hours! I forgot to reset the speedo after the last run but I guess we must have done about 8 miles during the day. During this time she behaved faultlessly and ran like a sewing machine. I did have to come off once for a short time when the grate got choked and I lost pressure but a good rake out and a blow up and we were off again. After that, I made sure to give the fire a good rake now and again to get rid of the ash etc on top of the grate. The new bush for the 2 to 1 lever has made a big difference to the smooth running when she is notched up. The new valves are working well and she just glides away with hardly a sound.

Yesterday was also the club public running day so Helen had to compete with two 5" gauge engines and a 3½" A1 but had no problems keeping up. It was a lot of fun actually and everyone was impressed with her performance. The way she is running now, I think she could manage to pull 2 or 3 passengers with no problem. I'll have to give it a try one day! We are having a do at the club on August 31st and inviting all the local suppliers who have helped the club over the years so that may be a suitable opportunity.

Next job is to finish the painting and get the tanks lined out. I haven't thought of the best way to do this yet and will have to give Chris Vine's book another study! I need to make a proper floor for the cab to give a wood effect and make some steps so the driver can get into the cab! I also need to get the injectors sorted once and for all. The 12oz Gordon Chiverton one works ok but uses far too much steam so I need to get an 8oz one working reliably.

08/09/2008

Bit of a gap again but this may be well be more or less the last update on Helen as she is now virtually finished at long (no pun intended!) last!

After reading Chris's book, I decided to give a low tack masking film a try for painting the lining. The film is called 'Frisk' and is available from most suppliers of artists materials and airbrush materials. It's a clear plastic film available in a roll coated with a low tack adhesive and stuck to a backing paper. It's used for masking off areas when airbrushing pictures, models, objects etc. The film is peeled off the backing paper and stuck onto the surface to be masked. The shape required is then carefully cut out with a sharp knife and the area to be sprayed peeled off, leaving the rest of the film to cover the areas not to be painted. The film is quite soft and cuts easily and cleanly with very little pressure on the knife so that the underlying surface is not cut or damaged in the process. The film comes in a gloss version and a matt version. I chose the matt version as it can be drawn on with a pencil or, in my case, printed on using a laser printer.

I decided to use it slightly differently and mark out and cut the film before attaching it to the tanks but this does make it a bit more fiddly to get lined up correctly.

The lining is fairly straightforward on Helen and consists of just a black edging to the tanks, cab and bunker. I was originally intending to add a thin white line inside the black but having done the black, decided it would look 'too bright' and stand out too much.

The method used was to draw out the tank sides etc. along with the edges of the lining and then do a test print onto ordinary paper, cut that out, and try for size on the actual tanks. This proved to be a good idea as my original drawings proved to be slightly different to the actual dimensions of the finished tanks! When I was happy that all the dimensions were correct, I printed the drawing onto a sheet of the film.

Outline of tanks and lining printed onto the Frisk film

Using a very sharp knife, the outline of the inside edge of the lining was carefully cut out leaving the backing paper intact. A second layer of the film was then stuck over the cut layer and the outline of the tanks cut out completely. The second layer of the film served to hold the bottom layer together until it was stuck in place on the tanks.

Film cut out and ready to stick onto the tank

Next was the tricky bit, sticking the film into position on the tanks. I found the easiest way was to just remove a strip of the backing paper on the bottom edge and this edge stuck into place on the tank. The alignment of the film could then be checked and when satisfactory, the rest of the backing was removed and the whole of the film pressed firmly into place. The top film was then peeled off along with the cut outer section of the bottom layer leaving the inside part of the bottom film in place. This is a bit tricky as the film sticks to itself better than it sticks to the painted surface and tends to pull off the wanted bit of film as well!

In the case of the rear bunker, the film was stuck on both sides and the end and all the lining painted by brush in one go. The black actually goes over the top of the beading on the top edge and slightly over the other side so this inside edge was masked off using low tack plastic masking tape.

The time to remove the film was a bit of a guess but I waited until the black lining paint had gone tacky and then carefully peeled off the film. The film left a very sharp edge to the lining with no bleeding underneath and I was quite chuffed with the result. It's certainly easier than using lining pens etc.

Tanks lined out and refitted to loco - must touch up those wheels!

 

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