Allchin Traction Engine Cylinder and Other Bits


This is a job that I did back in 2010 but never got around to writing it up. I was contacted by a chap ( Gary ) who had purchsed a part built Allchin but hadn't the facilities himself to finish some of the parts required. He had seen my website and asked if I might be able to help and I said yes.

The main item was the complete cylinder assembly. It had been started by the previous builder but a lot of the machining had been poorly done and several cock-ups made in the process. Holes had been drilled in the wrong place and too much machined off the main cylinder casting in a couple of places. Gary had had some of the holes bronze welded up quite neatly so they just needed cleaning up and redrilling. Some of the other mistakes needed more drastic treatment.

Actually, I can't remember now if more than one builder had worked on this as some of the work was fine.

Looking back through the photos that I took at the time it appears that I didn't photograph everything that I did and after all this time I've had to scratch my head a few times to try and remember what I did! Hopefully the pictures will jog my memory!

You can tell this was done some time ago as the Eagle mill is still outside under the carport.

The mounting flange of the cylinder had been machined to fit the boiler so I stuck it onto my own boiler to check that it fitted. Fortunately it did but you can see that the flange has not been machined on the top and is much too thick, more on one side than the other. So far as I could tell, the cylinder bore was in the correct position relative to the boiler itself. My biggest fear was that the bore would be too far to one side considering that the flange was lop sided.



The port face had been machined and the face that the valve chest sits on but no ports had been cut so I decided to do those next. I lightly marked them out and started with the exhaust port. The majority of the material was removed by drilling and then finished off with an endmill. In the photos below you can see where some of the wrongly drilled holes have been welded up.



I used a dial gauge as a depth gauge to measure the depth of the ports.



The steam ports were cut in a similar fashion.



The exhaust passage consists of a vertical bore from the bottom of the cylinder block up to the exhaust port and then a cross passage connecting with this to the front of the cylinder block. The vertical bore is blanked off at the bottom by a threaded plug. To position the vertical bore correctly, I stuck a piece of sticky tape onto the vice jaw and marked the width of the steam port on it along with the centreline. I could then aline the axis of the mill spindle with the marked centreline and the edge of the vice jaw.



The cylinder block was then clamped in the vice with the exhaust port lined up with the lines on the tape. This ensured that the drilled hole would be in line with the exhaust port.



The mill table was then moved across so that the hole would be the correct distance from the portface. The hole was then drilled and tapped for the blanking plug.




In common with most traction engines, the regulator is on top of the cylinder and the steam gets there by travelling around the cylinder liner and then through holes drilled in the bottom of the regulator chamber. These holes are quite awkwardly placed on the Allchin cylinder as they are at an angle through the bottom corner of the chamber. I thought it easier to machine the holes with a slot drill rather than try drilling into the corner.



At this point I decided to remachine the portface and square up the bottom face of the recess for the steam chest. I had noticed that the original face was not perfectly perpendicular to the original portface so this squared everything up and also machined off the blobs from the bronze welding repair.



I think on this next photo I am spotting through the mounting holes for the steamchest




Both the holes in the top of the steamchest were way out of position, mainly too close to the outside edge of the steamchest. The larger of the two is for the governor assembly and the other smaller one is for the check valve for the oil feed from the mechanical lubricator (had to look that one up on the drawings!)



I filled the holes in with brass plugs silver soldered in.


The steamchest was then temporarily bolted to the cylinder and the top of the steamchest and the top of the cylinder were then machined flush with each other. This surface needs to be flat as the safety valve casting bolts onto it.



I could then redrill the holes in the top of the steamchest in the correct positions. You can see below how far out the originals were. You can also see where too much has been machined off one side of the boss where the governor fits.



Back to the cylinder casting. The casting was clamped to an angle plate bolted to the rotary table so that I could machine the top surface of the bolting flange. Set up was a bit fiddly as the bolting face had to be aligned to the rotational axis of the rotary table. You can see where I had built up the casting with JB Weld where someone had taken too much off. Wonderful stuff. People have used JB Weld to repair full sized traction engine cylinders so it should be fine for this job!



Both ends of the flange were done like this and then the bit inbetween levelled off. I can't quite remember how I did that!

Next, the holes for the cylinder drain cocks were drilled and tapped.




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