The Burrell's Steamings 
June 2006

ModelWorks 4 inch Scale Burrell Agricultural Traction Engine 

Friday 9: I had planned to write this page up earlier but I have been so busy working on the Burrell I have not had time.   Whilst at the rally I was able to talk to some knowledgeable folk and I came away with ideas for improvements.  I now have plans to fix a knock I have been experiencing at high speed and  to get the injector to reliably pick up.

Like many other constructors I have been having trouble with the injector.  Over the course of the rally I only got it to pick up once.

I had a chat with Steve and he has been working towards a solution.  The route of the problem is that at 8 pints per minute the injector has a tremendous appetite for both steam and water.  The existing water cock has a relative small bore through the cock and Steve believes this is restricting the flow.   To remedy this Steve gave me a larger water tap that he is trialling.  Steve has since contacted to me to say that Tim fitted the larger tap and his injector now works properly.
 

Andy recommended fitting a smaller injector.  His rational was that an 8 pint injector would pump water in so fast that it would cause a large drop in pressure and no sooner than it was started it would be time to stop.  This rang true and the only issue remaining was what capacity to fit.  Polly has such an extensive range I was spoilt for choice.  Andy guesstimated that a 5 pint/min would work but suggested fitting a 3 pint/min JC injector.  This would enable the injector to be used in background without "shocking the boiler".  Another factor I had to consider was  the pressure rating of the injector.  In choosing between nominal ratings of 100 and 150 psi I plumped for 100psi as this should enable the injector to work at low boiler pressures.  (Andy thought there was a very good chance it would work at 120psi).  Rather than copy my choice I would recommend anybody looking for an injector to contact Polly Models as the issues are complex .

Dilemma
I now had potentially two viable ways ahead for the injector and had to decide which fix to opt for.  At first, fitting the new water tap and sticking with the supplied 8 pint injector seemed like the easiest option.  This became second favourite when I realised that I might have to adjust the length of the water pipe from the tap to the injector.  While the length of the replacement tap was the same as the original It would need different thickness packing washers to bring the tap vertical.  Therefore I chose to fit the new 3 pint injector and only disturb the water tap if this failed.  Any air leaks in the water feed would lead to certain failure.

Which ever injector I fitted I would have to make new pipework as I had allowed the bends to collapse when I re-bent the pipes to fit.  I was planning to make a pipe bender but at Steve's suggestion I brought one from Machine Mart.  It's a bit hard to find on their web site so here is a link to their Automotive Pipe Bender.

Andy recommended using soft pipe as it is less likely to collapse however I have previously avoided soft coiled pipe as I believed I could not straighten it. At Andy's suggestion I  rolled it between a board and the floor and was impressed with the results.
 

I cut the pipe over length and using the original pipe as a template bent it to shape.  I then offered up the pipe to the Burrell and determined position of the first union.  After I had silver soldered this in place I fitted the pipe to the Burrell and carefully marked the position of the remaining union.  It did not take long to make 3 perfectly fitting pipes and with the experience gained I would much prefer to make my own pipes in future rather that struggle with ill fitting made to measure pipes. 

Whilst running the engine at speed I was concerned to hear a knock coming from the works. Initially it was though it was the little end but closer inspection revealed the problem to be in the pump.  With the engine on slow tick over the pump connecting rod could be seen sliding in and out of the pumps piston by about 1/8".

Debbie had kindly sent me a replacement Oilite bush but I found it was a sloppy fit into the connecting rod.  I had left the problem go so long that the connecting rod itself was worn and I had no choice but to drill out the hole and make a replacement bush from phosphor bronze.  This is harder than Oilite and the presence of oil when I dismantled the little end indicates that there will be sufficient lubrication.
 

With the connecting rod free I could immediately see that there was a lot of play at the big end. This surprised me as with the engine assembled it appeared to be in good condition.  I tried to adjust the bearing but found this ineffective.  I soon traced this to a lack of clearance between the two haves of the bearing which I easily fixed with the aid of a file.

Once steam was raised I tried the new injector.  I was disappointed to find that it did not work.  Unlike the original it seemed to be short of water as anything more gentle turn of the steam valve caused steam to gush from the overflow.  In order to check the rate of water flow though the valve I removed the injector and found the flow to be excellent.  To my amazement on reassembly the injector worked and I conclude that there must have been a blockage in one of the pipes.  The  new 3 pint injector works well with both steam and water cocks full open though sometimes it is slow in picking up.  I put this down to the injector being heated by steam escaping thought the closed steam cock.  A blast of water thorough the injector and out the overflow seems to cool it sufficiently for it to pick up easily on the second attempt.  Thoughtout the session I had the injector working at pressures varying between 70 and 120 PSI.  I did not have the chance to try lower pressures and the situation did not arise where I had room in the boiler with the pressure lower that 70 PSI. 

When I ran the engine at speed I was pleased to find that the knock was gone.  What I had not expected was the the crank pump performed much better.  Previously I had had difficult with the clack valves bouncing on their seats and now they were operating with very positive clicks.  I conclude that this is down to the elimination of the backlash in the pump's connecting rod allowing  the piston to accelerate slowly at the end of start of the stroke.  With the backlash each stroke was kick started causing the balls to bounce.  The pump now delivers water and a substantial rate.

The engine is performing much better and I look forward to testing this for real on the field this Sunday during the Funday.

Sunday: I have just returned from the Funday during which the engine performed well.  I was asked to participate some time ago and declined because I do not have a suitable trailer.  My arm was final twisted when Brian was able to borrow a trailer.  On the day a second trailer was found and I was presented with a wagon train of two trailers.

As might be expected there were one or two minor hitches.  On one of the first runs  the gear change lever fell to bits - I was not even touching it at the time!  Fortunately it was only the end that fell off and it did not affect the operation of the gears.  It will be easy to repair as the failure was caused by faulty brazing.  I have experienced a number of brazing failures caused by poor heat penetration and I am suspicious this is down to the use of oxy-acetylene by MW .

As the day progressed I grew concerned by a an ever increasing squeak coming from the Burrell.  Slipping the engine out of gear showed me that it was not not in the engine.  I oiled up the second and third shafts but no matter how hard I searched I could not find the source of the squeak.  I continued using the engine and after half an hour it spat out the brake band and the squeak was gone.   It would seem that the squeak was caused by the brake band parting company with it backing.  From the look of the debris one end had become detached and was then pulled back under the band  

The Burrell acquitted itself well and it was nice to have a load to pull. The new injector worked but I did have trouble with it getting blocked with dirt in the water feed.  What ever the injector I would recommend checking for blockages in the water feed.  At the end of the day I had a chance to run the engine on open tarmac and I was able to do a nice turn of speed without distressing noises from the engine.  I don't know how fast I was going but it was faster than I can run.
 

Disaster struck when I fitted inside the tender.  Whilst tightening using the hex end the pipe collapsed. Obvious really I should not have put the hex head at the far end of the pipe.

Rather than sulk I immediately made a mark2 filter with the hex head incorporated into the threaded end.  I also reduced the number of holes to 254 (equivalent to one 16mm hole).  

A number of points follow from this discovery:-.

1. The stuck overflow valve was probably preventing my injector from working and explains why the injector originally worked and gradually became temperamental.

2. A fine water filter is required.  The 1mm holes in my new filter are probably too big. 

3. The internal works of the injector should be regularly checked and cleaned if necessary.  With the injector removed it should rattle when shaked up and down.

I have had to suspend work and prepare for the Model Steam Road Vehicle Society's Rally at Tewkesbury this weekend.