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September-2020
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"Traded an electric charger for this "Complete" (original) Cox Thimble Drome Olympic .15 engine. Right corner is photo as received."



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New guy here with all kinds of new guy type questions Empty New guy here with all kinds of new guy type questions

Post  Doug Quaid on Fri Jul 24, 2020 6:11 pm


I bought NIB PT-19 and got it to fly.  That was a "bucket list" thing.  I could never get mine to fly when I was 9 years old.

To be honest with you, the PT-19 was kind of hard to fly.  It will not fly without a lot of up elevator.

I'm trying to work my way up to flying the ME109  super-stunter, I managed to dive mine into the pavement at about 200 mph when I was 12 and that was as far as I got with it.

I also bought a Nomad and flew that. That is actually a really fun model and it actually flew over 1300 feet, I paced it off.  It's a lot more fun that it looks.

I also have a bunch of new and used engines that I got from here and there, including a NIB 010 tee dee and NIB-ish 020 baby bee

My problem is that these engines all either run like crap or don't run at all to varying degrees.

like when I adjust the needle valve, instead of speeding up to that nice high whine, they quit

I ran the 020 holding it in my hand and it got loose and hit the floor and now it wont run at all.  can't figure it out.

It's like these engines all have a decrepit part and are just limping along

IS THERE A GUIDE LIST ANYWHERE ON TO HOW TO OVERHAUL THESE ENGINES?

Just a complete list of what different things to do would be great.  

I want to refurbish the entire engine in one shot.

Also, how do you mount these engines for testing them?  just screw them to a board with tiny screws?  seem like that would be time consuming if you were testing the engine

is there anything special you need to do with the tee dee engines?  I'm thinking about running the 010

I'm using byron gen 2 race fuel that I doctored up with a few ounces (about 4.5) of castor oil to make 26% nitro, 20% lube, with lube being a minimum of 13.5% castor oil.  Plus I filtered it a few times through coffee paper.  I just noticed that I bought it in dec. 2018.  is it still good?  or should I get new fuel?

is there a diagram anywhere of how the needle valve works or what it looks like inside?  I hate not knowing.  or should I dissect one?

THANKS IN ADVANCE FOR ANY HELP
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Post  coxaddict on Fri Jul 24, 2020 9:49 pm

Welcome to this Forum!
Concerning how needle valves work here are some cutaways of the fine thread and standard thread needle valves and their respective spray bars from product engines with plastic back plates.  Screwing  the needle out allows more fuel to exit the spray bar hole.  Screwing the needle in will lean the mixture.  The finer thread allows for finer adjustment.
I would stock up on soft parts(gaskets, seals, reeds and fuel pick up tubes) so you can go through your engines.  Taking them apart is another story and many forum members can help you with that. Hope you're having fun!
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Last edited by coxaddict on Fri Jul 24, 2020 9:50 pm; edited 1 time in total (Reason for editing : add info)
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Post  happydad on Fri Jul 24, 2020 10:19 pm

Doug Quaid wrote:
I bought NIB PT-19 and got it to fly.  That was a "bucket list" thing.  I could never get mine to fly when I was 9 years old.

To be honest with you, the PT-19 was kind of hard to fly.  It will not fly without a lot of up elevator.

I'm trying to work my way up to flying the ME109  super-stunter, I managed to dive mine into the pavement at about 200 mph when I was 12 and that was as far as I got with it.

I also bought a Nomad and flew that. That is actually a really fun model and it actually flew over 1300 feet, I paced it off.  It's a lot more fun that it looks.

I also have a bunch of new and used engines that I got from here and there, including a NIB 010 tee dee and NIB-ish 020 baby been

My problem is that these engines all either run like crap or don't run at all to varying degrees.

like when I adjust the needle valve, instead of speeding up to that nice high whine, they quit

I ran the 020 holding it in my hand and it got loose and hit the floor and now it wont run at all.  can't figure it out.

It's like these engines all have a decrepit part and are just limping along

IS THERE A GUIDE LIST ANYWHERE ON TO HOW TO OVERHAUL THESE ENGINES?

Just a complete list of what different things to do would be great.  

I want to refurbish the entire engine in one shot.

Also, how do you mount these engines for testing them?  just screw them to a board with tiny screws?  seem like that would be time consuming if you were testing the engine

is there anything special you need to do with the tee dee engines?  I'm thinking about running the 010

I'm using byron gen 2 race fuel that I doctored up with a few ounces (about 4.5) of castor oil to make 26% nitro, 20% lube, with lube being a minimum of 13.5% castor oil.  Plus I filtered it a few times through coffee paper.  I just noticed that I bought it in dec. 2018.  is it still good?  or should I get new fuel?

is there a diagram anywhere of how the needle valve works or what it looks like inside?  I hate not knowing.  or should I dissect one?

THANKS IN ADVANCE FOR ANY HELP

Well, where do I start.

1. NEVER start an engine in your hand!!!  You will either cut a finger or BREAK your engine. Maybe that is what happened to your .020.  The crankshaft is very fragile and if bent, engine cannot work.

2. To refurbish an engine you need to completely disassemble the engine, removing all parts. Remove the piston , cylinder, glow head. Remove the prop drive plate, for the td’s, remove the collet holding the Venturi, spraybar and needle and spring. And remove the crankshaft from the crankcase.
   Now CAREFULLY clean all the parts in used fuel, or other cleaner of choice, but make sure that the cleaner does not melt the plastic Venturi. Do not use finger nail polish remover on the Venturi or it will be disfigured or melted. I personally use fuel that is “used”, fuel that I filled a tank with, but was not all used , so I pour it back into a container and use it later to clean parts. Not to be used in an engine run. The fuel looses nitro content, %, when exposed to air. Maybe even methanol %.

The fuel you use is close to correct. As I remember Cox recommendation is 20% castor oil
   If fuel is kept in a closed container in a dark cool area it still looses nitro % after being opened, but at a slow rate. I am no expert, but I would guess that after 2 years your fuel has lost a bit of nitro, maybe 2%, I’m no expert.

3. About the engine running, then when you adjust the needle usually means there is dirt or crud, old dried castor oil, in the engine, or tubing somewhere.  CLEAN IT.

4. I will try to draw crude needle + valve assembly drawing and repost in a few minutes. I use an iPad and can’t cut and paste.

Ask questions here. Google things, “how do I...”

Remember, Ask questions here, google search, ask questions here.

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Post  GallopingGhostler on Sat Jul 25, 2020 12:06 am

happydad wrote:The fuel you use is close to correct. As I remember Cox recommendation is 20% castor oil

That was back in the 1960's and 1970's, IMO when all fuel I bought was 100% Castor oil content.

It was may be 5 - 7 years ago, that O'Donnell Fuels (I think that's a Hobbico company) started selling Cox branded fuel on Tower Hobbies after Hobbico acquired Estes / Cox. Only problem was fuel was 18% with 2% as Castor, your standard mix for ABC engines, not genuine Cox formula.

Bernie, owner of Cox International (Canada) contacted Hobbico, let them know this was wrong for half-A engines. It should have been 20% oil with at least half or 10% as Castor. After contact, they corrected their formula.

The 10% synthetic oil has an added benefit of keeping down the Castor shellac build up on the cylinder and piston surfaces. The Castor protects during a lean run and the high temperature ball and socket joint of the conrod in the piston.

As you know, (and dang it I'm OCD too! Laughing ), all Castor is recommended if an engine is low on compression and depends on Castor shellac build up to retain compression, like in some of the old cross scavenge and Schneurle engines that have an iron piston running in a steel sleeve. Got a worn out Enya .15-III TV in that condition. (A shot of 40 weight motor oil in the exhaust port boosts compression temporarily so can hand start. Then amazingly seems to have the same amount of power as a good compression engine, go figure. sunny )

The discussion of the O'Donnell Cox fuel issue is somewhere in this forum. Just FYI, in case you missed out on this discussion.
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