Bogstandard Paddleduck engine

[Gordon]

I have made a Bogstandard Paddleduck engine and it is giving me fits on getting the bottom crank section to turn freely. I have remade both the crank throws and the bearing blocks. I can put a drill rod through the bearing blocks and the rod turns freely. The throws turn freely until I tighten the clamping screw and then it binds up on half the rotation. Obviously the connecting shafts between the throws is cocking and no longer perpendicular to the throw. Anyone who has built this engine have any works of wisdom? I tried making the bearing block bore oversize but I still had the problem. Maybe I have to make the bore even bigger. Thoughts?

http://www.machinistblog.com/bogstandards-paddleduck-engine-plans/

 

[kvom]

I had/have the same problem, and I think it goes with the territory. On mine I do as you and use a rod to align the bottom of the bearings. Then I assemble everything fairly loosely and then start to tighten the screws, all the while rotating the crank. If it binds, I loose that screw and tighten elsewhere. In the end, nothing is really clamped down hard, but I get it to turn. I think a better design would be to use ball bearings, which have some give in the races.

 

[Gordon]

I finally got the engine running. CCW only for some reason but that is another problem. I did as you said and loosened up the bearing blocks and I can actually see them moving just a little as it is running. I think that the next problem is in the valves. As most of you know you spend almost as much time tweaking as you do building.

 

[Gordon]

OK I am dumb as a rock but I am still having a problem with this engine. I can get it to run by putting air in the bottom ports on the valve block. I can actually get it to run on about 15 PSI using only one of the bottom ports. It will not run with air in the top ports. Half of the rotation goes around but as soon as it gets to bottom dead center it is working against air pressure and will not move. On the bottom port it is actuated through the recess in the valve and on the top port it is actuating through the hole through the valve. I still am not too sure about the operation of this piston valve even after reading the explanation on Blogs build log several times. I have read the notes on the log about the hole through the valve being too small and have what should be sufficient holes in the valve. I cannot understand why it goes fine in one direction and not at all in the other direction. Any thoughts?