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Author Topic: Cox Tee Dee diesel conversion  (Read 1926 times)
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I hate trees
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« on: August 22, 2011, 05:51:06 AM »

I was up at the 6th Area meeting where Pete Watson was flying his 36 inch Top Banana in Mini Vintage.  In the morning it was spiralling up to an awesome height, but it seemed to get worse and worse as the day went on.  It was just not able to hold a consistant pattern.  Although, he managed 4 mins in the flyoff, so he must have got a pretty good pattern then.

Pete had a dieselised Tee Dee in his Top Banana.  I recently remembered that I have a couple of Tee Dee 049s sitting somewhere.  I saw that there is a commercially available diesel head available on line.  Has anyone got any experience of these, or converting Tee Dees to diesel generally?
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PeeTee
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« Reply #1 on: August 22, 2011, 06:49:42 AM »

Adam

I have a Davis Diesel conversion fitted to a Cox 049 Medallion (not a TeeDee), but have yet to run it. It uses a PTFE diaphragm in place of the usual contra-piston and I was told by the chap who sold me the conversion kit that it was possible to use diaphragms made from beer can alu instead (I'll drink to that Grin). From memory there is another Cox diesel conversion available as well, but I don't know from who. Similarly I don't know whether either company is still in existence!

You might want to speak with Tony Shepherd who has a dieselised TeeDee and flew it in a TB. I think he found it to be very sensitive to trim/launch changes (thus inconsistent) and is now using a PAW 55 which takes the model to a great height on the MV allowed motor run. As his tame timekeeper, I can tell you that the Le Timide has a better glide.

Happy trimming (and see you at MW and/or the Southern Gala I trust)

Cheers

Peter
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TimWescott
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« Reply #2 on: August 22, 2011, 12:52:39 PM »

AFAIK Davis Diesel is still around.  I bought some stuff from him a couple of years ago -- phone only, clearly he's not interested in this newfangled web stuff.

I had a Davis Diesel head on a Golden Bee years ago, and it was a nice engine.  If you have problems that make the engine run lean it will eat those PTFE head gaskets, so lay in extras (I resurrected the engine but had leaks in the fuel system -- hence the 1st-hand knowledge).

I ran across Cox diesel conversion heads on the MECOA web site -- it may be worth a look, but I haven't used them.
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« Reply #3 on: August 22, 2011, 03:05:25 PM »

Adam

Here is the link to the "other" conversion kits http://www.mecoa.com/acc/diesel/index.htm

Hope you've recovered from your holdiday - your dad did well in France and had loads of luck in retrieving his coupes!

Cheers

Peter
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gossie
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« Reply #4 on: August 22, 2011, 06:30:53 PM »

The only experience I've had with a dieselised .049 TD was in the '70s when I put a Davis head on it and had the motor in a Keil Kraft Piper Super Cruiser.

Got it trimmed and flown, and then way up high on low compression the motor stopped dead and the model glided down with the prop. freewheeling.......it had busted off the crank pin.  I sold the head.

I do know these days some of the local guys have the reed motors with a diesel head on them with what they call a "killer crank".    Not sure if you can get it for TDs, and not sure where they get them from, but if your desperate I'll ask around.

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TimWescott
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« Reply #5 on: August 22, 2011, 08:05:18 PM »

The only experience I've had with a dieselised .049 TD was in the '70s when I put a Davis head on it and had the motor in a Keil Kraft Piper Super Cruiser.

Got it trimmed and flown, and then way up high on low compression the motor stopped dead and the model glided down with the prop. freewheeling.......it had busted off the crank pin.  I sold the head.

I do know these days some of the local guys have the reed motors with a diesel head on them with what they call a "killer crank".    Not sure if you can get it for TDs, and not sure where they get them from, but if your desperate I'll ask around.

They used to be available from Davis for the reedies.  Basically it was a Cox crankshaft without the relief for the counterweight, so the crank web around the pin had a lot more meat.

Dunno how necessary it would be for a TD -- although you certainly had a bad experience!
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dputt7
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« Reply #6 on: August 23, 2011, 03:43:31 AM »

Hi Fellas
This is a timely thread, I was just looking into dieselized 049's and was considering the Cox conversion found here  http://coxengines.ca/product.php?productid=312 they also do the "killer crank
http://coxengines.ca/home.php?cat=13
Its not a lot of money and I was curious how good they are. I would only be using it for scale or sport flying so easy starting and throttling are probably more of an issue than power.
Regards Dave
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« Reply #7 on: August 23, 2011, 10:31:11 AM »

Yes Dave, that's the one I saw.  I may buy one and have a play with it, I'm sure it will give me lots of fun and cut fingers!  You never know, it may even find its way into a model!.  As far as I can tell its only the reed valve engines that need a bigger crank, the tee dee should be ok.

Pete, I'm not back from holiday for a while yet, so I won't be at MW, but I should be at Salisbury Plain for the Southern Gala.  I haven't heard how Dad got on in France yet, not too well I hope, or I'll never hear the last of it....
Adam
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tonyshepherd
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« Reply #8 on: August 25, 2011, 04:53:01 AM »

Hi,

Yes, Pete's right, I had a lot of sensitivity issues with my newest Top Banana and a dieselised Cox though it may have been more consistent if I'd been running it under pressure which hold the revs better.  However, saving some weight, and a reliable PAW 55 is the route I eventually chose.  I know that Frank Rushby has been flying one with a Cox and have been told that he also suffered from inconsistency.

It has been suggested that the weak point of the Top Banana is the pylon which is only thin and can twist during the power run.  If I hold mine by the wings and give it a little wobble you can see it all flex which ain't good!

Cheers - Tony
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« Reply #9 on: August 25, 2011, 07:30:00 AM »

I remember reading about run inconsistancies with the Tee Dee's, both diesel AND methanol, that were traced to the original Cox needle valve.  The aftermarket onewith a finer thread, cured the problems for those who made the switch.  I can't, for the life of me, remember WHO made the NV's (Foremost? or even Davis?).
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« Reply #10 on: August 25, 2011, 09:58:05 AM »

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I can't, for the life of me, remember WHO made the NV's (Foremost? or even Davis?).

I know that Hank Nystrom the Texas Timer man does fine threaded NVs for Cox TDs, but there may be others. Hank has a website, but I don't have the link.

Peter
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« Reply #11 on: August 25, 2011, 11:33:53 AM »

http://www.texastimers.com/
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« Reply #12 on: August 29, 2011, 03:04:46 AM »

I believe they were originally called Kirn Kraft NVA's and were more applicable to the TD 049 and 051's; from memory they were 40 tpi thread and were made from brass and utilised a black plastic seal to stop leakage where it entered the spray bar.

The Killer crank works on the Baby Bee engines and are strongly advised if you want to run them as diesels and yes they will run backwards but that is a function of the reed valve induction system and not the nva.

Ployd in OZ
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« Reply #13 on: August 29, 2011, 06:36:09 AM »

Ployd is correct re. NVA.    I have a Kirn Kraft  here on a TD .051 that looks as described, and with the fine thread makes tuning the engine so better than the stock one.
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« Reply #14 on: August 29, 2011, 01:09:27 PM »

The Killer crank works on the Baby Bee engines and are strongly advised if you want to run them as diesels and yes they will run backwards but that is a function of the reed valve induction system and not the nva.

Cox reed-valve engines will generally start in the direction opposite the flip when you flip them in the forward direction, leading to much cursing, grabbing of spinners, and retries.

You can solve this problem by flipping the engine in reverse -- then it'll start in the direction that you flipped it, every time.
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« Reply #15 on: September 15, 2011, 10:05:00 AM »

Hi Fellas
Well I ordered a Cox 049 Diesel conversion Kit and a Killer Crank and it arrived down here in 7 days, that's good service. The kit comes with a set of instructions, a head , contra piston, 3 teflon seals (2 spare) and a foot of fuel line/ I also bought the crank and a mini tank that fits under the engine. So to night I spent a bit of time and put it together, most of the time was cleaning up the old reed valve engine that had been sitting around for many years. The only problem I had was with the prop driver being too tight a fit on the splined crank, the new crank was about .003" larger on the splines and it needed a bit of a light file of the driver to get it started on the crank. The new crank is quite a bit more robust and fits right in. It is suggested to use the starter spring but I always thought that was for wimps but it certainly works, after a couple of fires on the prime I discovered that I hadn't cleaned all the gum out of the fuel inlet. With this done it started straight away, It seems very responsive and will run quite slow, as I fly Free Flight Scale this is most important.I took a photo of it running but must have used the wrong shutter speed as it stopped the prop I was quite impressed with its power though and now I need to finish off 27 projects or so and build something to put it in. Been looking at some early Walt Mooney plans of a Rearwin Speedster and an Aeronca Champion, Ive already built his Long Wimpy and that's a nice model.
regards Dave
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« Reply #16 on: September 15, 2011, 10:24:23 AM »

Looks good Dave.

I found my diesel conversion kit and decided to use it on a Medallion, which I made up from spares purchased from a model shop closing sale. It's currently without spraybar and needle, which I've ordered from the same place (I assume) that you got your bits from, along with some spare Teflon seals. If yours only took 7 days to arrive, I should get mine soon.

I'll let you know when (and if Roll Eyes) I get mine running.

Cheers

Peter
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TimWescott
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« Reply #17 on: September 15, 2011, 10:43:49 AM »

I took a photo of it running but must have used the wrong shutter speed as it stopped the prop
You took the picture with flash, in a moderately bright environment that was enough to get partial exposure.  If you look closely you can see that the prop looks partially transparent, and you can see the gleam off the prop disk to the left and down from the engine center line.  The flash was very short, hence the stop motion -- the rest of the exposure blurred the prop thoroughly.

I've seen one stop-motion picture of a model diesel that captured the puff of gas out of the exhaust -- that was cool.
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Greg Langelius
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« Reply #18 on: September 16, 2011, 07:30:24 AM »

Modelers looking for a nostalgia 1/2A diesel engine can find a modern McCoy .049 diesel replica engine at PAL Model Products.

http://www.palmodelproducts.com/index.html

Greg
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« Reply #19 on: February 01, 2012, 10:38:47 PM »

I found the same problem with the driver being too tight-same fix,the crank endplay was also excessive and needed a thrust washer,non of the ones I ordered from Cox were big enuf to fit over the crank main journal and only sit on the step, so I filed a phenolic washer out to suit,I was not happy with this so machined a little step in the rear of the prop driver so it goes onto the crank a few thou further,std endplay is in the region of 5 thou,the Cox people now supply a couple of washers with the crank.
Engine is unrun as yet and waiting for a scale model to be built for it,engine is built from new parts to look like a Killer Bee.
The Mecoa RJL head has a o-ring seal which may be better than the teflon disc,I had one but made a conversion for a OS10 with it.

Phil
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« Reply #20 on: February 03, 2012, 08:45:09 AM »

I bought a DDD head for my TD, but also got a PAW .061 at the same time and later the .033.  I wound up flying the PAWs and never tried the conversion.  I love the good throttling, easy starts, and no worries about how well they will hold up.  I've still got the DDD head with a bunch of diaphrams but I don't think I'll ever use them.

Jim
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