Friday, December 18, 2020

Stepping Backward

I've been trying to troubleshoot why my Webster Internal Combustion Engine won't start since Sunday and still no joy.  You know the old adage about four stroke engines: we need Suck-Squeeze-Bang-Blow, with fuel and spark at the proper times.  "All I gotta do" is verify I get all of those at the proper time and in the proper amounts.  This week hasn't been "one step forward two steps back;" it has just been the steps back.

One of the tests I've done is to see if I get compression at the top of the piston stroke.  The prints say, "Rotating the flywheel counter-clockwise should produce a "snorting" sound through the carburetor as the intake valve lifts."  I can hear something, but I'm not sure it's at the right time.  I took off the intake/exhaust valve stack and if I put my finger over the combustion chamber port, it blows enough air to make snort/squeak around my finger on the compression (squeeze) stroke.  The way fuel and air feed into the engine is that during the suck stroke, the piston pulling back creates a partial vacuum, which opens the intake valve and that air flowing in creates the fuel flow in.  I've never seen the valve move while I'm cycling the engine.  That probably means the valve doesn't need to move to let air in.  It's not sealed and the air just blows in around the valve without it moving. 

Time to take that valve stack apart.  I started experimenting with adding a gasket between that block and the engine and I noticed something funny.  I had disconnected the fuel line from the carburetor and stood the tank up so that the tubes were sticking upward out of the top. I noticed that a metal weight that came on the fuel line was no longer in the fuel line, but just lying on the bottom.  It came out?  That's really in the "that's funny" category.

I didn't round up a glass bottle to pour the Coleman fuel into until about lunchtime today, and when I went to take off the top to pour out the fuel, found the plastics inside the bottle had come apart. Badly.

That black plastic thing, now in two pieces was used to seal the bottle by tightening that Phillips screw in the lid.  That's sure not going to work again.  The light blue fuel line on the brass tube and the much larger diameter light blue tube underneath and behind it were one piece when I got it. That tubing swelled in size until the metal piece fell out. I suppose if I had left it lying on its side much longer, it would have started leaking.

Obviously these plastics aren't compatible with the Coleman fuel!  I boneheaded the task and didn't check to make sure this tank was compatible with it.  The tank is fine, it's the rubber stopper and the fuel line that need to be replaced.  Just as obviously, I'm without a gas tank for now.  I've found some things that are compatible, but with Christmas shipping bottlenecks, I'll be lucky to have them by New Years.  I'll continue to work on the valves, I just have no way to test the engine until I get a gas tank.

While I'm here, for fellow watchers of the Starship work over in Texas, the last thing I posted was the next road closures were the Monday after Christmas, 12/28 through 12/30.  Sometime last night they added this coming Monday, 12/21 through 12/23, all are 8AM to 5:30PM.  They don't really say what those closures are for, but we might see Eileen move sooner than the last update. 


  1. Wow...I didn't think naptha would degrade those rubber parts like that. You'd probably want a tank for the fuel that the Diesel-powered models used, but it sounds like you have it under control.

    How did you lap the valves and seats? I know you covered it, but I can't remember how you did it.

    1. I found that company that makes the plastic fuel tank, Dubro, has a stopper that is rated for gas or diesel. It's their catalog number 400. Combine that with some Tygon gas resistant tubing and it'll be ready to rock and/or roll. Both are on order.

      Valve making and grinding was back in August, but I see I didn't write much about that. The valves fit in a guide, and are lapped by hand onto the mating guide. They're literally made for each other.

      I guess I fell into the trap of not knowing exactly how they should look along with with guys saying that the mating surface doesn't have to be big, a few thousandths is enough.

      The whole project has been continually making things I've never made and learning how to do it. I'd be disappointed, but not surprised, if I had to remake half the engine to get it to run!

  2. First thing, adapt an automotive compression tester to the cylinder. Someone should have ballpark readings. Second thing, spark timing. Set up a timing mark on the flywheel for top dead center on the firing stroke. I don't know if your system sparks on points open or closed, once you know that you can estimate initial timing setting. Then a timing light will let you dial it in closer.

    1. Attempts at timing were comparing the positions of the piston conn rod when the ignition cam fires the points by comparing photos. It's approximate, but nobody thinks it's critical.

      The spark plug I'm using is a motorcycle plug, a CM-6. Since it's a standard size, a standard motorcycle compression tester would use. There is no mention anywhere I can see of what it should be. That means no matter what I read, the answer is "so?"

      It's a 3/4 cubic inch, low power, low efficiency engine, designed to be anyone's first engine made from scratch.

    2. Putting a finger over the sparkplug hole to seal it should reveal any compression as you rotate the engine. The carb needs to be wide-open to minimize any inlet restriction. If you have good ring sealing and good valve sealing, it should try and blow your finger out of the hole. I have no idea how much compression a small engine like that should produce. My old Toyota can generate about 170PSI when cranking. I'd guess yours would be much less!

  3. The intake valve is opened by the vacuum. Is it held closed by a spring? And if so, is that spring too strong? I've never run into such a system, but I would guess that the spring tension would be absolutely critical.

    Sorry if this has been covered before. I haven't been following the engine build that closely.

    1. The intake valve is opened by the vacuum. Is it held closed by a spring? And if so, is that spring too strong? I've never run into such a system, but I would guess that the spring tension would be absolutely critical.

      It is held closed by a spring, which I made. The plans say .013 music wire and I used the .015 I had. The guys on the forum I read who have made one of these engines say it shouldn't be an issue, which is why I used it.

      There are some videos of these on YT and in some, like this one, you can see the intake valve moving very freely.
      On mine, I've never seen it move more than tiny amounts. One of the forum gurus says his hardly moves perceptibly, but I'll work on this a bit assuming it's stuck open and doesn't really seal at all.