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Pee Wee .020 cranks?

Old 09-27-2009, 08:05 AM
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Mr Cox
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Default Pee Wee .020 cranks?

Just wondering if it is okay to run the stock Pee Wee crank on diesel?

Not looking for high revs and will try to be careful with the compression screw...
Old 09-27-2009, 11:06 AM
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lildiesel
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Default RE: Pee Wee .020 cranks?

The Pee Wee crank is actually pretty robust for a small glow. I've flown them with as large as a 6x2 or 6x3 wooden prop on motorglider-like planes and 1/4A sized Old Timer FF (radio assisted) off and on for years. I've also broken a few cranks messing around with the DDD .020 head back in late 80s/early 90s. The crank pin takes about 1/3 of the shear web with it. I don't recall breaking a con rod.

All I can suggest is running a larger prop to keep the revs down and not increasing compression beyond just what is necessary to get the engine started. Matter of fact, back it off after starting to the minimum where the engine keeps running. Avoid protracted bench running. Just learn the starting drill and then go flying.

Of the current Cox props still available try the black 5x4 or the 5x3 or even a grey 6x3 with the Tee Dee spinner and screw. Using the Cox grey 4.5 will just encourage tuning for glow like revs and help you break a crank pronto.

Here's one of my Pee Wee's sporting the DDD head. It's just a curio to me now and might be available to a good home. The DDD head, not the Pee Wee!
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Old 09-27-2009, 12:03 PM
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Default RE: Pee Wee .020 cranks?

Thanks for the information. I've just gotten a two DDD conversions for .049 (with the stronger crank too) and one for the 0.020. Mine is red and goes well with the tank.

With one copper gasket it fired right up on a prime with out even engaging the head screw onto the contra piston. Might be a little too high on the compression?
I'll try 5x3 -6x3 props and see how it goes. I'm planning to put this in Cub that is overpowered with a stock peewee on glow. So I'm hoping the diesel and a larger prop will be a better match.
Old 09-27-2009, 02:07 PM
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Default RE: Pee Wee .020 cranks?

I knew there just had to be something I forgot to mention.

You might want to try adding a couple of head gaskets just to see how a larger prop will run. I wound up running with two gaskets for the teflon discs and three or four when I experimented with discs cut and carefully sanded from beer can aluminum and K&S brass sheet. There are two gaskets and a hand cut teflon disc in the Pee Wee pic I uploaded.

The best alu disc I ever messed with was cut from the bottom of a can. It took its own combustion chamber shape when flipped over with a prime and the screw out all the way. It did not deform easily when the compression screw was turned down, so I added gaskets to decrease compression and then took them out to tune the running. Thinner alu from the sides of a can would adjust with the screw as did the brass sheet.

BTW, the translucent white cap from a new glow head makes a great place to store your discs as well as checking the roundness of your work. I also put my DDD head in one for storage.
Old 09-27-2009, 02:21 PM
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Default RE: Pee Wee .020 cranks?

Okay, thanks.
I was hoping I wouldn't have to fiddle with these tiny gasket any more when going to a diesel. [:'(]
Maybe I'll reduce the size/length of the contra instead, or simply make another one in a lathe so that I can get back to square one if it doesn't work...
Old 09-27-2009, 05:29 PM
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Default RE: Pee Wee .020 cranks?

Homemade diesel conversion for a Cox 020.

This might help someone! Ray
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Old 09-27-2009, 08:11 PM
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lildiesel
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Default RE: Pee Wee .020 cranks?

Interesting diagram. Could you tell us when and where it was published?

It reminds me of the diesel head I made out of an RC Charlie's .049 head ages ago with just a Dremel drill press and a few flat files. Not too successful, but at least it fired and burped. Now I've got my sweet little Wen Mac Mk II in front of me and with the diesel muff-like cylinder head off wondering how much work it would take to make a diesel conversion out of another head if I could round a second one up. Just putting an old experimental brass diesel disk in raises the compression noticeably... hmmm. Next sunny day I should do some flipping with fixed compression just to mess around.
Old 09-27-2009, 09:24 PM
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Default RE: Pee Wee .020 cranks?



I'd say Aeromodeller sometime in the 70-80's. Sorry can't be more specific than that. The local free-flighters have been doing it to Cox 0.020's for years with considerable success.

Should work with any screw in head engine including Norvels. The way I see it a plain aluminum disk is all thats needed for a contra-piston. Softdrink can metal is "plastic" enough to deform where you want it too yet still retains enough "elasticity" to respond to changes of compression via the comp screw. They have a relativity short life but are easy enough to make in a batch. They clamp betwwen the top of the cylinder and the screw in head.

Ray
Old 09-28-2009, 10:00 PM
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Default RE: Pee Wee .020 cranks?

Correct-IIRC it was a guy called Pete Meleg (or similar) who wrote the article. I'll have a look at my Aeromodellers tonight when I get home from work. I'd guess late 80's or very early 90's

'ffkiwi'

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