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Post  roddie on Wed Oct 21, 2020 7:28 pm

gkamysz wrote:Haha that's great! It just needs a substantial spring somewhere to keep that cylinder in check.

Yes.. and BTW.. awesome thread Mark. Is there the possibility to fit an OEM exhaust-shield between the cases? I lost my pics.. but it's a stamped-steel part shaped the same as a case gasket.. and having a protrusion designed to deflect hot exhaust gases. Maybe it would provide a friction/detente for your faux cylinder/needle.

Why does the rear glowhead loosen-up? Maybe another gasket or two would help?
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Post  roddie on Wed Oct 21, 2020 8:39 pm

Here's an image of the Bee engine's exhaust-deflector.

Here. Hold my beer. - Page 2 Exhaus13

or..

Here. Hold my beer. - Page 2 Exhaus14

A short piece of wooden-dowel in-between with a flat/notch filed might stay in place.. at a minimal weight penalty. Basically a friction-collar.
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Post  batjac on Wed Oct 21, 2020 10:50 pm

Great idea, Roddie! Not between the cases, but between the Goldberg mount and the rear case. That should work. Let me think on it for a while. Maybe a thin sheet of cork or rubber to rub against the cylinder. I should have some cork sheet stashed away somewhere for either clarinet repair, or Mosin bedding.

The Craftsman Mark
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Post  batjac on Fri Oct 23, 2020 2:15 am

Continued:

With the back case in place I screwed in the needle valve to see where the fuel nipple is.  I then marked the position and drilled a hole in the bottom of the rear case.  

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Then I put the two cases back together.  

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For reference, I measured the weight of this engine against an 8cc tanked Bee.  This engine is only 0.45 ounces more than the tanked engine.  2.35 ounces vs. 1.9 ounces for the Bee (68 vs. 54 grams).  

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For the faux plug I dug around the old engines box looking for a bad glow head and found an engine with a glow head missing the filament.

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Everyone wanted to know how I was using the cylinder to needle the engine.  The obvious method I was going to use was with a piece of fuel tubing to rotate the needle valve.  I didn’t want to ruin the existing needle on the reed valve assembly. So I dug around and found a spare fine needle.  I cut the top off of this and then slipped a short length of small fuel tubing over the stub.  As I said, I didn’t like my first idea.  So I just did a quicky change to try out my new idea.  All I did was cut a shim from a cookie tin for the fuel tubing to go through.  The fuel tubing sticks out of the top and when I put the faux plug on, it compresses the fuel tubing and traps it.  Thus, when I rotate the cylinder, it rotates the shim and the small fuel tubing attached to the needle.  I started off by opening the needle valve three turns, then installed the cylinder in the case backed out ¾ turn from all the way in.  Then I tightened the faux head down.  Unfortunately, I had a little too much fuel tubing sticking above the shim, so the head didn’t tighten down as I’d hoped on the test I did the other day.

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Now that I know the idea works, I pulled the tin shim and made a new insert from brass shim stock.  I took a glow head gasket and put a tape backing on it.  I trimmed the tape around the outside of the gasket and taped it to the shim.  Next I used a Sharpie to mark the outline.  After that I drilled out the center for the fuel tubing and then trimmed the insert to the same size as a glow head gasket.  I put the insert in place and pulled the tubing through the hole.  Installing the faux head seemed to do much better with this brass shim and it tightened down much better than the tin shim did.

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Lastly, I went ahead and dug out a cylinder heat shield and installed it between the rear case and the Goldberg mount.  I have to admit that Roddie’s idea to use the heat shield to provide friction resistance to the cylinder was be…  ***ahem***  Was bet…  ***cough***  Was bett…  ****wheeze***  Was bette… ***hack, cough***  Was equally as good as my idea, and I went with his instead.

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The Congested Mark
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Post  rsv1cox on Fri Oct 23, 2020 7:25 am

roddie, Mark; roddie, Mark; roddie, Mark. Two heads are better than one especially on model engines.

Good one Mark!

Bob
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Post  getback on Fri Oct 23, 2020 8:07 am

Way to improvise Mark and another Good helping idea from roddie !! Have you ran it since the upgrade ? The weight came in good . Babe Bee .049 Small Cox Logo
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Post  KariFS on Fri Oct 23, 2020 9:43 am

I think this is the most elegant ”faux twin” that I have seen. Would look really good on a sport scale biplane or a model of one of those old small aircraft that had an inline twin.

Now that the ”rear face” of the engine block is flat, it would be possible to make a radial mounting plate using maybe 1/8” aluminium. Countersink the screws on the back, and drill mounting holes maybe in a tanked bee or horseshoe pattern. Would make it a little bit more robust, considering the extra weight and moment compared to a standard 290 engine, and the possible brittleness of the Goldberg mount Two Cents

Anyway, just wanted to let you know that I am quite impressed by the ingenuity involved, and even though there were not many greenies, I am sure I am not the only one Thumbs Up
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Post  Oldenginerod on Fri Oct 23, 2020 8:09 pm

Just a reminder of the "original concept" picture I posted which prompted Mark's build.  
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I also found another.  This time we can try to figure out the tank/intake arrangement.  Interesting to note it has the exhaust shield on the rear cyulinder as Roddie suggested.

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