Re: How to build a high-performance Cox .049 Engine

**RknRusty** Mon Nov 28, 2011 9:58 pm

microflitedude wrote:What is the best reed material for maximum high-end RPM?

From what I've read, most people seem to agree on mylar. Just check it for rough edges left over from having been stamped. I've had to scrape the edges on a couple, but not lately. I always test it in both directions to see if it works best one way or the other. They eventually get a little bowed. If I re-use one while working on the engine, I make sure it goes back in the same way. You can visually tell which side was against the venturi hole.

The steel ones last longer but they cause more wear on the tiny boss that encircles the venturi hole. And I wonder if the increased mass causes them to be a little slower to react. That's only a guess on my part, its ability to open and close may be well inside the RPM capability of the engine. The teflon is said to be less durable. I have one of each, but I've never tried either of the teflon types. I don't have high expectation for the woven teflon. But you might want to try teflon if you are thinking of entering the Tach Race. I don't think any of the modern reeds work as well with the circlip retainers. I think they don't open very well. The old copper star reeds had a lip on each edge that gave it more freedom to move under the clip, but I don't think any new stars, if they even exist for .049s, are made like that.

microflitedude Tue Nov 29, 2011 10:33 am

RknRusty wrote:
microflitedude wrote:What is the best reed material for maximum high-end RPM?
From what I've read, most people seem to agree on mylar. Just check it for rough edges left over from having been stamped. I've had to scrape the edges on a couple, but not lately. I always test it in both directions to see if it works best one way or the other. They eventually get a little bowed. If I re-use one while working on the engine, I make sure it goes back in the same way. You can visually tell which side was against the venturi hole.

The steel ones last longer but they cause more wear on the tiny boss that encircles the venturi hole. And I wonder if the increased mass causes them to be a little slower to react. That's only a guess on my part, its ability to open and close may be well inside the RPM capability of the engine. The teflon is said to be less durable. I have one of each, but I've never tried either of the teflon types. I don't have high expectation for the woven teflon. But you might want to try teflon if you are thinking of entering the Tach Race. I don't think any of the modern reeds work as well with the circlip retainers. I think they don't open very well. The old copper star reeds had a lip on each edge that gave it more freedom to move under the clip, but I don't think any new stars, if they even exist for .049s, are made like that.

Thanks, that is what I was looking for.

nitroairplane Tue Nov 29, 2011 5:19 pm

The star shaped one do exist!

**RknRusty** Tue Nov 29, 2011 6:45 pm

nitroairplane wrote:The star shaped one do exist!

With the tiny bend at each tip to allow free movement? Any old ones I have are long flattened so I can't show what I mean.

Jaspur_x Tue Nov 29, 2011 9:23 pm

Would you be so kind as to share where we might obtain such reeds at?

**RknRusty** Tue Nov 29, 2011 10:06 pm

According to the article, the newer mylar rectangles with the rounded edges work best. The ones Bernie and Matt sell.

microflitedude Tue Dec 06, 2011 10:20 am

How do you install a driveplate on a KB crank? In the article, it says to tighten the prop screw and it will draw the plate evenly onto the crankshaft. But since the threads are softer, will this still work? How tight can you go?

Thanks, Matt

nitroairplane Tue Dec 06, 2011 11:13 am

microflitedude wrote:How do you install a driveplate on a KB crank? In the article, it says to tighten the prop screw and it will draw the plate evenly onto the crankshaft. But since the threads are softer, will this still work? How tight can you go?

Thank, Matt

Yes I am sure it will work.
I do that with all my cranks.

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