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KK Cobra 0.8cc

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Post  Oldenginerod Thu Mar 09, 2017 1:42 am

I would think that, if the bluing action oxidizes the surface, then removing the blue from the inside of the cylinder will also remove a small amount of oxidized metal. I would suggest that you allow the mating parts to do the polishing if any blue forms on the inside. That way, it will only remove the minimum necessary from the surface. As mentioned, I use a small paint brush. If any liquid inadvertidly makes its way to the inside surface I just rinse and leave it there. It has never effected the piston fit or performance of any engine I've blued.
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Post  KariFS Thu Mar 09, 2017 1:58 am

Some time ago there was a discussion/speculation about reproducing complete Cox engines (Space Hopper was considered a good candidate) or parts using a CNC system, and earlier in this thread Mark's brilliant idea about using a Cox backplate with a cobra-style crankcase.

So, how about this: Who's the first to manufacture a crankcase that would convert a postage stamp engine to beam mount? Essentially it would be a Bee case with mounting lugs, it would use a modified (or unmodified) postage stamp backplate such as this:  

KK Cobra 0.8cc - Page 2 Image15

I think, with a modified intake and the fine thread needle valve this would make quite a hot and interesting little engine, and would give new life to all those forgotten RTF engines that people have in their junk boxes.
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Post  jmcalata Thu Mar 09, 2017 4:52 pm

Ian, you already run the Cobra ???

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Post  Mudhen Thu Mar 09, 2017 7:39 pm

@KariFS wrote:So, how about this: Who's the first to manufacture a crankcase that would convert a postage stamp engine to beam mount? Essentially it would be a Bee case with mounting lugs
Answer...well kinda...Dale Kirn.
It wasn't manufactured, but in the early 60's Dale took an RR-1 and modified it to what he called the RR-2. He machined away the fuel tank-front and fashioned a needle valve assembly to fit in the venturi. Then he cut Space Hopper beams and mounted them to the RR-1 case. He said it was a great runner, but Cox had little interest because of the release of the Tee Dee engines. (I have one of the crankcases and carburetor bodies around here somewhere.)
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Post  ian1954 Mon Mar 13, 2017 10:09 am

@jmcalata wrote:Ian, you already run the Cobra ???


I ran it up on 20% nitro and a 5x3 keil kraft nylon prop. It peaked at 16,000 revs but was unsteady. I got a steady run on a 5x4 kk prop and 15% nitro at around 14,500 revs.

I didn't spend too much time with it - just wanted to make sure it was a runner. It is quite a rare little beast and I didn't want to mess about with shims.

Jose, I hope you are not a mathematics teacher - this engine is not 68 years old - more like 57. In your video you referred to it as "grandad" - it is only eight years younger than you. More like a brother than a grandad!
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