Texaco Running Steady

Hi, Mud.
My first thought was the tiny flat-ring gasket on the venturi tube's tip may be leaky. When the fuel level drops below the tube and where it fits into the air intake hole, air leaks causing the fuel's head pressure to change.
Just guessing.
Rusty

Hi Rusty
I added a second venturi gasket already but problem persisted?

Thanks
Iceberg

Mudhen wrote:If after you tune the engine it begins to reduce rpm on its own, then it means the crankshaft to crank case fit is too tight.
To solve the issue. Start the engine, leave the glow plug clip attached.
Tune it to a medium rpm, let it run for 15-20 seconds, then detune it to a slow rpm and let it cool down. Tune it again to a medium rpm, then let it cool
Do this for about two or three full tank runs.
After, start the engine, tune it to peak rpm for about ten seconds, then detune it, as before.
It should loosen up after five or six runs.

 I am sorry but by the time you do all that and it mite work (( i would take the engine completely apart and clean )) this means removing the crankshaft too !! Also check the side to side play at the prop washer end of CS .

getback wrote: I am sorry but by the time you do all that and it mite work (( i would take the engine completely apart and clean )) this means removing the crankshaft too !!  Also check the side to side play at the prop washer end of CS .

Good point, Eric. The crank bushings could be worn down enough to be leaking crankcase pressure when it heats up. Have you noticed if it has a nosebleed? Like oil and fuel dripping from behind the prop-drive plate?

EDIT: Not really bushings, but the aluminum nose tube serves the same function.

I have dissembled many NIB Cox engines and the crank is black from whatever, it needs a polish and the bore also.
You could maybe avoid pulling the crank by soaking the crankcase assembly in Hoppes 9 and flushing with fuel.

.

Mudhen wrote:If the engine tunes relatively steady, then begins to slow down on its own. It’s usually a friction problem.
It can be misleading because as the engine slows, it cools. When it cools, it wants to increase rpm.

This is interesting, I am anxious to see if a good break-in fixes the problem.
Does the propeller size affect the friction problem?

Is there a clear advantage to using Sig CHAMPION 20% or 25% ALL CASTOR
on Cox engines?

Mudhen wrote:
So the engine may sound, and act, as if it has an air leak, or fuel metering problem.

That's what I thought after I read the original post. I am curious if the
problem got worse after taking apart the engine.

Iceberg wrote:
I added a second venturi gasket already but problem persisted?

Why replace the venturi o-ring? or double it up. Did it look deformed?

I have always flat sanded the rear of the crankcase to eliminate a vacuum
leak, and replace the gasket if it is damaged.


Bill M.

I added the other venturi gallery wondering if there might have been a vacuum leak i added with existing making two of them definitely no leak there. Didn't change the "fanning" I have pulled apart yet but will to bleak. However didn't feel right? I'll be sure to let all know soon.
Thanks
Iceberg

Hi Gents
I opened the tank to disassemble and clean all. Found that the fuel line had risen up in the tank. Because fuel line was new that I replaced it was so stiff it lifted up in the tank. I guess that was why it died after 1 minute. I'll do a test run in a day or so to see if being forced back to 8 oclick position fixed it. I'll be sure to let v all know. Thanks for input.
Iceberg

Perhaps same problem with this:

https://www.coxengineforum.com/t11907-need-help-troubleshooting-a-cox-049-engine

Sounds like you got it, Ice.

If it still does it, take that dang tank off and replace it with a backplate and an external tank, just as a test. That should eliminate all of the problems that make the integral-tanked engines so maddening. Those built-on tanks can make you waste more of your life than it's worth.
Rusty

Hi Guys
Did a test run last night with the motor. It ran 4 minutes on just Uber two turns on the needle. It held poetry good but still slowed a couple times a few hundred rpm then sped up again. I'm pleased it for fire minutes without stopping. I was told a Texaco might run 5-6 minutes. Anyone else got a comment?
Thanks
Ice

What size prop are you using?

6-4 Cox grey one

Iceberg wrote:6-4 Cox grey one

It’s supposed to swing a larger prop. Less RPM = better fuel economy.

The instruction sheet says 7Dx3.5P for a 5-6 min run time.

Where do you find one of those 7D x 3.5P props i looked but so far can't find one? I need two actually i have a pair of Texacos?

Thanks
Ice

You can even go larger-8x4...which are available from Bernie and co....here in NZ we have people using slo fly props on texacos-at only 4-5000rpm and getting very good fuel economy....but this is in the 1/2a texaco event....you have to decide what purpose you intend using your texaco engine for-it was developed purely for this event-so if you use it just as a 1/2A reed valve-you're probably setting yourself up for disappointment.....ie its not just a Babe bee with a pretty tank and crankcase, its been optimised for extreme economy at low revs-treat it as a normal reed valve 049 and it will come up short.....

ChrisM
'ffkiwi'

PS the people here who are serious about the event will spend a lot of time testing, mixing and matching parts from several texacos to get one that gives the best possible economy with good reliability....you rarely get both elements in a Texaco straight out of the box

The Cox 7x3.5 is somewhat of a tough prop to source. This was the go to prop for the TD .09. They were made in both the softer black and the harder gray plastics. The gray ones don't take much abuse to break them. As mentioned the Texaco could swing a 8x4. Some users of this engine also use APC electric props like the 9x4.5.  Just as a side note,  8" props are typically the largest size propellers allowed in the Texaco free flight events. Master Airscrew makes a 7x3, 8x3. The weight of these props would concern me a bit over the Cox props. The Master Airscrews are under $3.My next concern is the hole size, they may require a bushing to fit the screw. The 7x3 might fit correctly but when you get into 8" props, the hole sizes start becoming larger due to their use on larger shafted engines.Master Airscrew changes annually and the prop you bought last year may not be the same as current offerings. I just noticed the newest series of GF series props are more to my liking as they recently started to offer more blade area.

   A standard practice breaking in a Texaco was to use a Cox 5x3, 5x4 and run in the engine using this prop and 3 head gaskets prior to running larger props. Run about 6-10 runs on this prop rich. Switch to the 7x3.5 and lean it out. You should be getting about 9500 rpm's on this prop. The 8" prop is going to be about 2k rpm's lower. Glow plugs have a tendency to come loose on this engine so always check it for tightness.

    As far as your run times are concerned, from 1995 and on Cox enlarged the venturi diameters on the Texaco engine. Most users preferred the smaller pre "95" backplate for extended run time. Adding additional head gaskets will also extend your run time but might sacrifice starting ability a bit, experimenting is everything as engine condition and piston/cylinder fit is equally important. Many who use this engine use a full synthetic fuel with about 7% nitro to prevent varnishing.  15% nitro seems to be the percentage used due to easier starting and slightly longer duration over traditional 1/2A fuel. Higher nitro is going to shorten your run time.

Hi Ken
Thanks for the information. Useful.

My largest prop I have in stock -s a 6-4. since I'm over here in Korea not for sale. However I saw some 8x4 propellers out of China might they be ok? They will deliver here to Korea.

Last night I took two 6x4 props and used a long screw and washer to put them on in an X. I ran that and got 4 minutes 30 seconds. It ran 30 seconds longer. The prop wind flow was pretty decent better than with single 6x4. The motor didn't fan. Once or twice it slowed only slightly. I guess trying to catch up fuel supply but ran actually pretty good. It also ran 1/4 turn further leaned out than with a single 6x4. My Texacos are the older versions with the smaller venturi i think. I collect different ones. I want to have a motor that will run 4-5 minutes for better flight times. I might order some 8 x 4 props and see maybe it will lean a bit further and get 5 minutes. Seems possible.

Thanks
Ice

I'm not a user of Texaco engines and I have never flown the event. My club had numerous older members who flew these events belonging to the SAM free flight association. Our last member passed away last season. However, much of what they had and information has been passed on to many of us who would attend the club meetings and social events. I talked with one of our free flight guys this past weekend who passed the info that I just posted. Without personally seeing the engine, it's difficult to offer helpful information. Do you have a piece of fuel tubing over your needle? This is very critical on these engines especially the Texaco. You need a clean cut and square piece of tubing to seal any air leaks at the backplate.

Not knowing the props available to you, it's difficult to offer a yes or no answer. If it's all that you have to work with, there's not much of a choice other than to try. One thing that I find a bit concerning is that you have applied two props to the shaft. I would suggest not to do that. Prop hubs are typically not true or parallel to one another unless you trued them. In doing so, you could ultimately introduce a lot of vibration and load to the shaft that it wasn't designed to handle. This could cause it to break and shear off or it could wobble out the case quite rapidly.

NIB Cox Texaco engines typically came with a metal bushing and a longer screw for larger props, there's a guy on eBay I don't recall his name but he makes metal bushings and metal  carb bodies for TDs you may be able to get metal bushings from him. Kustom Kraftsmanship also used to make a competition COX Texaco engine. Those engines are  like hens teeth but you may be able to find one of their back plates with the fine thread needle valve with a shroud which reduced air leaks and got you better tuning.

Ken Cook wrote:Without personally seeing the engine, it's difficult to offer helpful information.
Do you have a piece of fuel tubing over your needle? This is very critical on these engines especially the Texaco.
You need a clean cut and square piece of tubing to seal any air leaks at the backplate.

While exploring this site, the .PDF download in the Sticky:

https://www.coxengineforum.com/t753-the-revised-2011-gibeault-mouse-race-program

Is great information on air leaks and engine set-up that applies to
any reed engine. I especially like the recommendation to replace
the crankcase paper gasket every time the engine is disassembled.


Bill M.

I prefer ultra silicone, or 3Bond 1107B over rtv silicone.

Gentleman
After all your appreciated comments and suggestions. I tried them. The Texaco continued to have occasional problems. So I took the needle valve out took the spring off forced a soft nitro hose over it and a washer and put it back on. The motor stopped its silly fanning and runs steady now. I guess the needle valve was allowing occasional air to drop the fuel flow or something. I have two 8x4 props coming over on a transport flight in a couple weeks to Korea. Then I'll try the Texacos with the 8x4 I do hope to see the run time improve to close to 5 minutes.

Wanted to let all know what was the repair for that one.
Thanks
Ice