[solved]Breaking in a new Tee Dee #4 - question

Ken Cook wrote: Rusty, are you saying the case is weeping at the drive plate while running? This obviously is not an ideal condition. How about that 0-ring aluminum body? That may prevent some of that from passing. Ken

Right, weeping behind the drive plate, sometimes it even looks like a spray.

After I put the aluminum carb on it it wouldn't keep running, just shutting off for no apparent reason, so I put a plastic one back on it and it was better but not great, kind of like it is now. In fact when I flew it last Saturday it shut off in mid flight with the plastic carb. So that's when I decided to tear it down. I was wondering if my bladder tubing had gone bad, but the Streak ran fine on the same stuff.

Generally speaking, when I have an engine that just shuts off I look at the plug first to be suspect. Is this a high time case? I don't really recall seeing font end leaks on my Tee Dee's. I have plenty of Fox .35's that do that. I'm quite sure this could certainly lower performance. I just don't think it would cause the engine to just quit. If you have any air leaks around the threaded portion the venturi screws into I would look at that area closely. I'm puzzled as to why the aluminum body was problematic. I've had very slight fitment issues with them that were easily resolved, but the runs were impeccable. I also have fixed many of the plastic style by using K&S tubing and carefully making a collar out of the tubing. This method works amazing as it squeezes all the cracks back together making the venturi nice and tight again. Prior to slipping the collar on, I rough it up on the outside and clean with solvent then I use epoxy prior to the ring slipping on. Here are some pics. Ken

Ken Cook wrote: Generally speaking, when I have an engine that just shuts off I look at the plug first to be suspect. Is this a high time case? I don't really recall seeing font end leaks on my Tee Dee's. I have plenty of Fox .35's that do that. I'm quite sure this could certainly lower performance. I just don't think it would cause the engine to just quit. If you have any air leaks around the threaded portion the venturi screws into I would look at that area closely. I'm puzzled as to why the aluminum body was problematic. I've had very slight fitment issues with them that were easily resolved, but the runs were impeccable. I also have fixed many of the plastic style by using K&S tubing and carefully making a collar out of the tubing. This method works amazing as it squeezes all the cracks back together making the venturi nice and tight again. Prior to slipping the collar on, I rough it up on the outside and clean with solvent then I use epoxy prior to the ring slipping on...

I was thinking maybe the head too. I haven't swapped it out yet but that's next on the list. It's probably a high time case, but I agree, just sudden shutting off isn't what I would expect either, rather low but steady crankcase pressure. Even though it's not feeding fuel on suction it could still pull extra air around the threads. I inspected the new carb body under the magnifying lamp for fractures before and after I installed it, no visible cracks. I was thinking of a bead of permatex front and rear of the carb body. I have another new plastic one I can try before I go buy tubing. There's not much else it can be. The backplate is tight. I'll try another bladder too, I have several fresh ones tied up.

Rusty,

There is a thread on RCU technical Cox question and BMatthews has a post which might offer some insight to this. I am not sure but it looks like it could be a possibility.

Good luck,

Bob

I'll see if I can dig it up, thanks.

You CAN run that combo but due to the limitations of the reed style intake and the extra length of the choke tube style intake you will likely not see any RPM gain over the more simple two bypass flute style cylinder.

The increased compression may or may not work out. You'd need to try it. If the increase in compression combined with the less than true "small prop" Tee Dee style RPM results in firing too early you'll simply beat up the engine and not see a gain in RPM.

For example even with a Tee Dee the high comp head needs a fairly free running prop. The one time I ran my own Tee Dee for a lot of runs on a model using a 5x3 prop it ran like crud for the first few flights. Eventually it darn near stopped. Seems I'd been getting so early ignition that I busted the seal on the plug. I replaced it with a regular straight cone style plug and it ran much stronger and smoother immediately. Never looked back and have not seen a need to try another high comp head for the sort of flying I do.

Oh, I tend to run at LEAST 25% nitro for my 1/2A engines all the time other than on my Tecaco models where it's 5%.

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I was having trouble getting a link to work so I just printed the post itself. Hope it helps. This is from the 1/2a moderator BMatthews over at RCUniverse.

Hope i'm not stepping on any toes with this.

So maybe I have too much compression with the new cylinder/piston. I put it back together with only the 2 shims I was using with the old set. I'll experiment with shims and heads this evening before I try anything else.

It runs fine now. I tried 4 shims with the same head and had no improvement. I put a Babe Bee head and two shims on it and it ran an unwavering 18.4K for the full run. I put another 1702 head with two shims on it and it held 19.4K with no nonsense for the full run. Not real fast for a Tee Dee, but fine for my purposes. The Chopper shall fly again.

Hopefully this coming Saturday morning will be dry and calm enough to take some planes out. I want to try my little Kom-Bat too. It has the Black Widow I tuned up last winter, and may be one I enter into the Tach Race.

If it runs well on the bench but has over heating symptoms in the air you may have some fuel foaming. (Notice how I suddenly know about this?) A little Armor All in the fuel works wonders.

Bob

I'll keep that in mind, but in an airless bladder, it shouldn't be able to foam. Same with a pressure-less party balloon bladder if you evacuate it before filling. My Bean/Medallion would cough and sputter with a wedgie but ran smoothly with the balloon. That may be why. I didn't know why at the time, but it's probably the reason I gave up using the wedge.
Maybe I'll revisit the wedge in the future. Maybe not.

Forgot all about the bladders. I guess I am still too excited about beating the foam issue after about 25 years.