Bog's Paddleduck Engine

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sbwhart:
Well done Kirk

That engine really looks the business :thumbup:

Now your down to the fine tuning bit you'll soon get it running.

Have Fun

Stew

Stilldrillin:
That`s looking good now Kirk! :thumbup:

David D

kvom:
It seems thje large the engine, the more metal is rubbing together and the more there is friction to overcome. After I took one piston and both crossheads out of the driveline and oiled up everything, the mechanism turns pretty eadily. I did run it on an electric drill for a minute or two.

To reduce the friction in the crossheads more, I opened up the mounting holes in the top plate and polished the guide bars: 3 grades of abrasive tape and then scotchbrite.

In yet another way to construct a piston and rod combo, I made a new rod threaded only on the crosshead end. I then took the existing piston, which fits the cylinder well) and reamed out the threaded hole to 3/16" to match the drill rod. I was hoping for a press fit, but got a reasonable sliding fit. But the rod and piston should be straight. When I fitted the combo into the cylinder and gland both slide well. However when I screwed the rod into the crosshead it became evident that the threaded hole in the crosshead is not perfectly vertical. However, there seems to be enough play in the crosshead guide bars that it will work. So I put some loctite on the piston/and rod, and am waiting for it to dry before seeing if the entire mechanism can be made to turn freely under hand pressure.

Once I get the engine tuned it may make sense to replace the loctite with a silver solder joint.

kvom:
Another day of "fiddly stuff" in the shop, interspersed with watching Roddick beat Murray at Wimbledon (sorry you Brits! :ddb:)

Getting everything to turn smoothly with so many moving parts and sources of friction can be a little frustrating. The first thing I noticed was that the flywheel was rubbing on the base plate, as I had milled the flat for the set screw a bit too narrow. It also seems that every time I took something apart to fix or adjustt, on replacement something else would bind. The next item to need attention is the bottom corners of the eccentric straps, which catch on the base plate from time to time.

In any case, I now have both pistons adjusted, and will try to get to the valves this weekend. I have to go out of town for a few days starting Sunday, so I'm not sure when the first trial run will be.

kvom:
Finally got back to the shop after some days away tending to family business. I made a pair of support bars from 1/3" square brass bar, to do away with the temporary 4 screws serving as feet. Then back to fiddling.

First fix was to ream out the through holes on the stream chests, as a couple of the screws seemed to be binding and promoting a small gap between it and the block. Then I noticed that one of the cranks was hitting the center opening in the base plate, so I took off the plate and enlarged the width of the hole by .100".

After reinstalling and connecting one connecting rod only, I found that the mechanism would turn easily in one direction, but stick in the other. It seems that the connecting rod angle is greater in one direction and thus induces some binding when trying to raise or lower the crosshead. If I turn the engine upside down then it will turn in both directions, although less easily in one direction.

Currently the guide bars are a smooth sliding fit in the crosshead holes; I'm wondering if reducing their diameter would allow increase or decrease the tendency to bind.

I could also tune the engine to run in the "good" direction to run it in, and then switch the air supply to test out the reverse.

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