Burrell SnippetsModelWorks 4 inch Scale Burrell Agricultural Traction Engine |
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| I have divided this page in order to keep in down to a manageable size. The previous snippets are available here. | ||||
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January 2007: "Little Beastie" has been laid up since the end
of August and my thoughts are now turning to the 2007 season.
August was far too early to pack up but I found it difficult to
identify suitable rallies at the end of the season. This year
my predicament it worse as the Detling Steam Fair is no more.
My intention is is to attend a rally every 3 to 4 weeks. Currently I am
catered for up until the end of July but have no prospects for August
or July. I consider the obvious choices too big and
suspect they will be unable to give miniatures a chance to
play. Please contact
me with any suggestions. |
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I had though fixing this error to be impractical but whilst at Ally Pally I spoke to Tim about the impressive changes he had achieved to his MW Burrell that he was exhibiting. The beauty of Tims Modification is that it only requires changes to the funnel and no changes to the base or smoke box. To date I have generated an artist imprison of what I could achieve. I was all fired up to start when I herd on the grapevine that ModelWorks might offer a modification kit. I am tempted to go it alone as I can't wait to get my engine looking right - watch this space.
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Since buying the "Double B" injector I have been studying the principals of injector operation. My most useful reference is "The Model Injector" by Ted Crawford especially the theory section at the font. I have learned that I could shift the operation range of my JC injector to help it pickup at 120PSI by adding a thin shim behind the steam cone to increase the annular gap. Out of the blue Terry, from Double B designs, contacted me to say that he is offering a re-coning service for the original ModelWorks injector which has proved successful on a number of ModelWorks Burrells. I am now faced with a dilemma as I potentially have three working injectors - well there is always eBay. Before fitting any injector I need to ensure that I have decent water filter as my current attempt leaves a lot to be desired.
I managed to buy some fine gauze on eBay. I have rolled this into a 1 1/4" dia tube secured with hot glue stick. To support this I have fabricated a carrier from brass that has a 1/4 BSP thread so that it can be directly fitted inside the water tank. I estimate the holes in the gauze will restrict particles larger that 0.02mm (8 thou). If this proves too big I have some even finer gauze but I am concerned that this will clog too easily. On examination of the picture of the fitted filter it looks like I need to paint the inside of the tender. |
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12 February: I have
decided to go ahead with the chimney modification and have ordered the
necessary materials. I will use this page to document the
modification, though in the future I may create a separate page.
The following two diagrams will help to explain how the
modification works.
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The secret of the modification is the replacement chimney base ring (red) which has an integral collar that extends downwards over the existing flange. To give the impression of two mating flanges the collar has a narrow slot machined half way up. When I was deciding on the proportions of the modification I was fortunate to find a line drawing of a full size Burrell single. On the right hand drawing the MW chimney is shown in green. The scaling between models and full size is exactly 3 to 1. I have included the drawing in higher resolution as it deserves careful study. The red outline shows the outline of the proposed modification. It was not possible to make the new base ring exactly to the dimensions of the real Burrell as I am not changing the existing chimney base. The first issue is that the chimney base is too high. To partly overcome this the collar on the new base ring extends below the existing flange. This has the beneficial effect hiding the top part of the base casting making it appear fatter. There is a limit to how far this can be taken as the width of the dummy flanges are now over scale. Rather that match the outside diameter of the flange I decided to keep it in proportion with the existing base casting. On the right hand drawing I have scaled the proposed modification so that the outline of the chimney base matches the full size Burrell. I have got he proportions correct except for the increased width of the flanges. Even though the parts will be slightly smaller than true 1/3 scale dictates I hope by observing the correct proportion to fool the eye. Currently my Burrell is a very free steaming and I have concerns that
fitting a larger diameter chimney may affect the drafting. I am
particularly concerned at the step change in diameter where the new
chimney meets the old flange. If this proves to be the case my
design includes the provision to include and inner cone to smooth the
transition to the new chimney. |
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After seeing how rusty the inside of the tender was when I fitted the water filter I decided to give it a through wash followed by a coat of Hammerite. Rather than go for a drip fee "perfect" finish my goal was to give everything a through coat. With my arm though the inspection hole I could not see what I was doing so I painted by dead reckoning. Every now and again I checked progress using a pocket mirror. Since making the float it has become an indispensable aid to gauging how much water is in the tender. My plan was to make an improved version but I never got round to it until now. My latest version ensures the maximum range of movement and I have trimmed the rod length so that when none is showing the tender is empty. I had been experiencing problems with the regulator leaking and it as got to the point where the engine will run with the regulator shut. Before resurfacing the valve I made close fitting aluminium plugs to stop off the passages into the engine with the aim of preventing debris entering the works. Using a flat steel block as backing I worked my way up from 120 to 1200 grade wet and dry paper. I achieved a near mirror finish though for some reason it is not clear in the picture. This made it worse - see below. I have always been irked by the fitting of the hose to the water lifter as it puts excessive strain on the hose. Originally the hose exited horizontally and this required a sharp bend in order to coil the hose onto the tender. To improve the situation I remade the union incorporating a 90 degree bend so that the hose exits downwards.
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On Wednesday I took the engine to the park for a steam test and on Saturday I attend celebrations in Dartford to mark the unveiling of a plaque to Richard Trevithick. With 3 steaming in 6 days it is not surprising that I encountered problems. Towards the end of Saturday afternoon I was horrified to look down and see I was about to lose a tyre. Subsequent examination showed that the Isoflex had failed to take onto the smooth inside rubber surface of the tyre. After my usual soul searching I decided to replace the tyre using the same method as before. In order to give the Isoflex a better chance of taking to the inside of the tyre I cut groves using a small burr in my mini drill. I also found that my efforts to prevent the regulator leaking have made matters worse. With the regulator closed the engine runs at a medium tick over. However the serious problem is that if the engine is left stationary it becomes completely steam locked. To investigate I coated the regulator valve with engineers blue and rubbed it on the valve face. This showed me that I had rubbed a concave depression by over enthusiastic use of wet and dry paper. I believe the depression was caused because I used relatively short strokes with the wet and dry paper. Inevitably more is taken of at the centre of the stroke than at the end. Rather than concentrate on surface finish I should have ensured that I got the valve face flat.
To enable me to better gauge the surface flatness I made a longer dummy
regulator and with the engineers blue I could see the location of the
high spots. It took me 3 days of patient scraping and checking to
get the surface reasonably flat. I then improved the surface
finish with a limited number of long strokes using 240 grit wet
an dry on a 1 3/8" long backing block |
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I obtained the chimney top spinning from GA Hopkins & Sons Ltd as spinning copper is beyond my capabilities. All the other parts I manufactured myself. The most arduous task was turning a new chimney base ring from 120mm cast round bar. It started life as a heavy lump and ended up quite light with the bulk in the workshop vacuum cleaner. I decided to make and fit the inner cone as fitting it later, once the chimney was covered it soot, would be a messy job. Whether this is needed I will never know but the intention is to avoid an abrupt change in diameter at the base of the chimney. My thinking is that this area could be critical as it is immediately above the blast pipe. I made cardboard templates for the sheet metal work and this enabled me to check my design prior to cutting metal. I used 1mm thick steel sheet for the chimney which fortunately is within the capacity of my guillotine/rolling bars. I revited the seam using rivet bolts obtained from EKP supplies. Other than painting the only task remaining is to make an adaptor to
enable the extension chimney to be fitted. |
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I am glad to say the new chimney performed much like the old one though I believe the engine note was improved. My rebonded tyre stayed on and the regulator was much improved. It is not perfect as if the engine is left to stand for a while enough steam builds up in the vale chest to enable a few strokes. |
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