Monday, November 2, 2020

It Was Working So Well There For About 45 Minutes

"It" being my Webster Engine.  Not running on its own with a little Coleman fuel and oil mix, just running with the crankshaft driven by an external motor; a battery-powered drill. 

I ran it for the better part of an hour yesterday, but the drill ended up running more than the motor.  A couple of times, the chuck loosened enough for the engine to stop turning and one time the battery had to be swapped out to be recharged.  I think I got a solid 30 minutes on the Webster turning, but whether it ran 35 or 55 I have no clue.  So today I thought I'd run it again and after about 10 more minutes, the motor stopped turning that crankshaft throw and moving the piston. 

Since I put this together, my goal has been to do just this and run in the engine.  I have my fuel tank, and the carburetor is on the engine in this video. I need to get my ignition points, assemble my ignition system, assemble the fuel tank and start getting it to run. From the first, though, I've had problems with the crankshaft throw.  There comes a time when you've wasted more time trying not to scrap a part than it would have taken you to make a replacement.  Or a half dozen replacements in this case.

Today, I broke out the original files I used to make this one and I'll make a replacement tomorrow.  I cut the original shape on my big CNC mill last May but I hadn't made a note of the tooling I used.  That meant I had to read the coordinates out of the G-code and see how offset they were from the drawing coordinates.  The problem with the one I have is that the crankshaft isn't perpendicular to the aluminum sector so that it wobbles every rotation.  It was perpendicular until I put in the bushing, clearly I didn't have the metal body parallel to the floor in my milling vise.  The wobble's visible in the last 10 seconds of the embedded video.

While I'm a month (?!? I hope!) from running this model a few times, I'm thinking about what to do next, another, more involved ICE, or perhaps a Stirling inspired by JPL's KRUSTY?  Doubt I could get the nuclear reactor, though.  Or perhaps something completely different?


  1. Moving parts is a step. I see 2 main ways forward. 1) A one piece tour-de-force crankshaft. 2) A one piece crank spindle with an integral hub that has the crank throw and pin attached in some way. You may recall some time ago we discussed the assembly of roller bearing 2-stroke crankshafts using surface plates, v-blocks, indicators, presses and big mallets. Piece parts are just so undisciplined that way.

    1. I do recall. These are low power engines; they're about 1/2 cubic inch so I'm sure they wouldn't make 1/4 HP. Not enough to require a one piece, steel crankshaft. The main tradeoff in my mind was whether to pin the one I have or start over with one that doesn't wobble as much. I don't see any reason to keep the one I have.

      One of the guys I've been inspired by silver soldered his throw (a different profile) onto the shaft, which I'm not set up to do because mine is aluminum. OTOH, one of the things I thought of yesterday was to make the next one out of brass. The next one will be pinned onto the shaft with a spring pin.

  2. Stirling powered by a solar dish? Stirling that vibrates on blade springs rather than having rolling contact bearings?

    1. At this point, I don't know nearly enough to design any sort of Stirling.

      Since KRUSTY takes a piece of Uranium 235 as big as a roll of Bounty paper towels ("KRUSTY -the quicker picker upper") I couldn't afford that.