I initially assembled the linkage with all the joints unpinned, so I could check that it all fitted and could move freely without any obstructions.
Disaster!!!
The angles that some parts of the motion were moving through were clearly wrong. The pendulum levers - which support the expansion link, and the link hangers were both visibly wrong.
I checked all the components against the drawings - and discovered that the weighshaft -which supports the link hangers had been located in the wrong place on the frames- a dimension of 13/32 on the drawing had been set out as 13/16 in. (Actually, by the original maker of the frames -but I was supposed to have checked it). Everything else was correct - but -adding up the various dimensions on the drawing showed that the centres for the link hanger brackets were in fact wrong -by 1/8 in. Still, it made me read up and understand how Stephenson link gear is designed.
To make matters worse, I'd drilled all the mounting holes around both items,and the new holes would run into the existing ones. I thought about scrapping the frames -a lot of work - and of silver soldering fillers in, or getting them welded in. In either case, I think the distortion would have ruined the frames. As I had space to spare inside the frames, I made up doubler plates for the frames, using the existing holes as the attachment points, and fitted the brackets (shortened) to the inner plates only. You can only tell if you look inside the frames. I don't think the strength is in any way compromised, and the motion is in its original position. All the motion now looks right, including the operating angles.
I then set the expansion link to the mid position, (at only this point, there's no movement transmitted from the expansion link assembly to the valve gear). Then, with the intermediate joints and the hanger brackets at right angles, and drilled and pinned the joints. I used 1/16 taper pins - and was glad when I was finished and the taper pin reamer was still in one piece. (I held it in a pin chuck, and cut very slowly, with lots of cutting oil, and cleaned the reamer frequently.)
Then, with an airline connected to each cylinder in turn, and using very little pressure -only a few psi - and with the valve coupling links and the main connecting rods removed, I operated the piston valve, driving the piston from one end to the other (and through the cylinder end plates if you use too much pressure). Also, its seriously a time to keep fingers out of the way. I used a piece of plastic tubing to listen for air escaping from the cylinder drain cocks, to determine when the valve opened in each direction. I measured the valve crosshead position, and calculated the mid point. Then, without disturbing anything, I could measure the distance required between the valve connecting rod centres. By comparing that with the actual length of the valve connecting rod, all I had to do was to move the valve on the spindle by the required amount -and knowing that the thread on the valve rod was 40 psi, I knew haw many turns and flats to turn the valve lock-nuts by. It was quicker to do than to describe. I finally fitted the valve coupling rod.
Then, with the gear in full forward position, and the crank-axle at forward dead centre, I adjusted the forward eccentric until air could just be heard at the front cylinder drain cock. I locked the eccentric in position, and rotated the crank axle to back dead centre, and checked where the valve opened. It was a few degrees late, but I left it for the moment.
I then repeated the whole thing for the reverse eccentrics, with the reverser in full reverse.
Then repeat the lot for the other cylinder.
I then fitted the coupling rods, and again with only a few psi of air to both cylinders, rotated the crank axle wheels, and could feel that the valve events were about right.
So, standing well clear, and with the wheels clear of the bench, I increased the air pressure to 30 psi or so, and things started to happen! It initially needed about 60 psi to get the engine to run reliably. After only 10 minutes running, it would run on 30 psi, and eventually on less than 20 psi. Its surprising how much difference a few minutes running makes.
Once the engines freed up, I then repeated the valve setting procedure, making minor adjustments. I thought that the valve positions weren't exactly right, as the valve events weren't quite equal for the two halves of the cycle. I was able to rotate the valve rod which is threaded onto its clevis position, to get the valve position just right. (Again, a temporary measure, but easy to do and get it right. Then I found that, as I reduced the pressure, the engine would always stop at the same position - again, small adjustments of the eccentrics and the valve position helped. Once I was satisfied that I'd got it as right as I could, I dismantled the valves, and tightened up the clevis pins -four flats -which I was then able to correct for on the actual valve adjusters.
Now it was running properly, I could lock up the eccentrics permanently - I removed each grubscrew in turn from the eccentrics, and replaced them with one which I'd drilled right through in the lathe. I used this as a guide, and drilled into the main crank axle. I then removed the drilled out grubscrew, enlarged the hole in the crank axle, and fitted new screws, with a protrusion turned to fit the holes I'd just drilled.
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