Cox rotary valve starting procedures?

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Cox rotary valve starting procedures?

Postby RobH » Mon Apr 02, 2007 7:58 am

I was wondering if anyone knows the correct amount of (starting)turns for the needle valve on a Cox .010 and .020 tee dee rotary valve engine? I started up some new in box (vintage) units and found the amount of needle valve turns to be much more than I'm used to. Could this be an indication of an air leak? Also was wondering what the correct thing to do with the crank case pressure nipple upon starting? I'm not using it to pressurize a tank - so should it be plugged? I found it easier to start with it plugged but it ran fine opened up? Any advise would be much appreciated!
RobH
 
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Postby Jim » Mon Apr 02, 2007 10:18 am

The crankcase pressure nipple is not active until the underlying metal shaft bearing is drilled through. This, of course, entails first dismantling the engine completely to ensure that any resulting swarf can be completely removed ... and shaft pressure isn't the greatest benefit, anyway. Suggest you forget about it.
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Postby RobH » Mon Apr 02, 2007 11:35 am

Thanks for the info. I'll take your advice and leave them the way they are. A bit cranky to start compared to other 1/2 stuff I have played with. Took about 8 turns out to start, with 1/2 turn back to smooth out once running. Most of my other engines took about 3 turns needle to start.
RobH
 
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Postby gossie » Fri Apr 06, 2007 4:48 am

I have no problem with either .010 or .020 TD Cox engines, as long as you use at least 25 per cent nitro in the mix. 30 to 40 is even better.

As suggested, forget running them on pressure, it doesn't prove much on them, but it's worthwhile on the .049/.051s when used for competition.

I would never use the Cox nipple on the front though. Much better to use a backplate with a nipple in it, or drill one of the mounting lugs with a 1/16th drill and insert a 1/16th OD alum. tube into it with a touch of Cyano. to hold it in.
gossie
 
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Postby RobH » Fri Apr 06, 2007 12:02 pm

Thanks....any idea how many turns of needle you are using to start them? Most of my engines use around 3...except these 2 - they are taking as much as 8 turns! I was thinking maybe it was an indication of a problem. The engines were brand new vintage.
RobH
 
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Postby gossie » Fri Apr 06, 2007 6:35 pm

Not sure about needle valve turns open. But does it really matter if they are running at 'full song'?

They only other thing I can think of is that they have been run and the venturi is clogged with old castor, blocking some of the fuel from coming in, so you need to compensate by opening the needle valve wide open.

Take the carb. apart and take a look how clean the very small holes in all the parts are.
Hook up a piece of fuel tube, wind the needle right in and as you blow hard open it, and see how far when your breath will go through.
gossie
 
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