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Old Jan 17, 2008, 02:35 AM
Registered User
Luebeck Blanqensee, Germany
Joined Aug 2004
12 Posts
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Fuel for Cox engines!

Hello!

I bought 2 Cox shure start engines.
Itís hard to buy the Cox fuel here in germany. You canít get it here. I donít know why.

I read that the Cox Engines need pure castor oil fot the lubrication.
Nearly 100% ;o) of the fuel is made with synthetic oil.

Original Cox Sprit:
For warm days
15% Nitromethane, 20% Bakers AA degummed Castor Oil, Rest Methanol.

For cold days
30% Nitromethane, 20% Bakers AA degummed Castor Oil, Rest Methanol.
From: Larry Renger, ĄCox Guruď

My questions:
Can I use fuel with synthetic oil or do I damage the Cox?

Can I use other fuel?
Like the Fuel for the diesel engines.
A third of Ether, a third of rizinus and a third of Petroleum?
Has anyone some experiences with fuel like this?
Please have in mind: I donít have dieselcylinder-head for the cox!

I want to replace the nitromethane by another liqiud. Ether (aether) is maybe a possibility, I think. It is also hard to buy nitromethane here in germany Ö

Thanks for helping!

Holger
From Germany
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Old Jan 17, 2008, 05:03 AM
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Nikolash's Avatar
Velika Drenova also Zemun, Belgrade, Serbia
Joined Nov 2007
134 Posts
Best fuel for cox is 20%castor with 10-20%nitromethane

Synth oil shuod be used in samll percentage(2-5%) to prevent polimerisation of castor oil.

Higher percentages of synth oil are good until you run too lean.

Straight fuel (no nitro) is good (especialy for larger props 6x4-7x3), enviroment, health friendly.

No diesel for now and that setup, that is another story.

I addmit that today is hard to find nitro fuel with only castor oil.
If you have access to raw materials (rizinus, methanol -pharmacy suppliers; and nitromethane-availlable at lindinger, maybe scweighofer too)
make your own fuel.
You could buy a liter or two of heli or boat fuel (20-30%+nitro more is beter), add methanol, castor, and make your own fuel. About 10% percent Nitro, 6% synth, 14% castor


Practical advice:
Contact FAI modelers (ie control line combat) they use castor oil based fuels.
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Old Jan 17, 2008, 07:10 AM
Registered User
Luebeck Blanqensee, Germany
Joined Aug 2004
12 Posts
Hello!

Thanks for the answer!

...
Straight fuel (no nitro) is good (especialy for larger props 6x4-7x3), enviroment, health friendly
...

Does this mean, that I can use onle rizinus and methanol for a Cox engine?

Holger
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Old Jan 17, 2008, 09:00 AM
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Velika Drenova also Zemun, Belgrade, Serbia
Joined Nov 2007
134 Posts
Ofcourse, it will run quite well, when tuned right.

With nitro, starts on first flip, more forgiving on needle setting, partialy discharged glow batery, flight attitude, weather conditions etc
in one word more consitent work of engine with more power(rpm).
Realy hassle free!

With no nitro wouldn't always start at first flip, you have to exacrly open needle, prime it (not too much, not to low), you should always have fully charged batt etc

Option without nitro requires more attention on engine, with nitro on yourself.

In each case you shold play some time with engine to get know ech other

Those little engines are cheap, but If you respect them, they will not let you down, Ever!

I wish you Good Luck!
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Old Jan 17, 2008, 08:08 PM
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Joined Dec 2007
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If you have 15% synth oil 4 stroke fuel over there can add some castor to bring it up to 20%. Even a little castor gives protection against a lean run.

In the US castor oil is sometimes used as a medicine and small bottles, 125 cc or so, can be obtianed through pharmacies. You can also buy castor off the internet.

Tom
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Old Jan 17, 2008, 09:39 PM
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Western KY
Joined Sep 2003
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Holger --

The smaller displacement engines will perform better and more reliably with 15% or better nitro fuel. I generally run around 22.5%. COX fuel or similar blends are also getting more difficult to locate here in the States -- the demand has fallen due to the move toward electrics in the small plane market and hobby shops are just not carrying the 1/2A fuels.

Although small engines can overheat, they tend to run cooler than the larger engines -- adequate oil content can reduce damage to a certain extent if they do get too hot. However, the COX ball and socket design used in the rod/piston assembly needs a fairly high oil content, particularly a high film strength lubricant such as castor oil, to run for a long time. The rod/piston fit on recent batches of Sure Starts has been quite loose and without a "sticky" oil with good film strength, the joint will wear prematurely. Also, the pistons on the more recent batches seem to be softer than the earlier engines -- the sockets reset more easily than the older motors.

You do have another option. I have been using high nitro/low oil content car fuels (20/10 and 30/10), then adding pure castor oil to bring the total oil content up to about 21%. It works out to about 17% castor oil by volume with the remainder being synthetic.

The last two boxes of Sure Starts I purchased needed to be thoroughly cleaned internally -- all were full of swarf and cutting lube. When cleaning, I'll remove the crank and check for any embedded chips in the thrust bearing, polish the crank lightly, reset the piston/rod socket, clean all parts well, true the back of the case (remove the ridges left when the case was tapped for backplate screws) and check to be sure the backplate screws don't bottom out when tightened. I also replace the prop screw with a 5-40 socket head cap screw. On the later engines, the ball socket has tended to loosen during breakin and needed resetting a second time. The piston does seem to work harden over time and the resets are needed less frequently.

There were some engines shipped over the last 6 months that had the zinc based cases -- identified by flutes on the nose and a flat grey color. These tended to show more wear around the crank bearings than the extruded cases. The weakest part of the Sure Start design is the piston socket and the lower end of the rod. I've had failures at both ends -- castor oil is one of the best preventatives.

A 6x3 is the most you should try to turn with these engines. A 6x4 is too much load and a 7" can stress the crank -- the crank will tend to fail at the web just below the pin.

5x3, 5.5x3 and 5.75x3 will work well.

andrew
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Old Jan 18, 2008, 11:30 PM
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Keremeos, BC Canada
Joined Mar 2004
2,639 Posts
yeah, 6-3 is fine for reedies, a 5 1/4-4 is ideal IMHO, ya just have to find them...

Mind you, I am not sure that the new engines are built to the same specs as the old ones, so oil content is likely to be critical.

It's like the old Mills75: the Doonside75s were quite superior to the original, the Aurora was a mile off, I owned all three at once so I could compare. If you ever get your paws on a Doonside, never let go! I suggest that the Cox engines and their various manufacturers will have the same problems with build quality.
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Old Jan 19, 2008, 12:24 PM
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Joined Nov 2005
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i use sig 1/2a fuel with added castor oil 1 0z to the quart it runs great you can also use car fuel with added castor oil im using 25% i haved used 6x3 - to 7x4 props on my cox engines with extra head shims with no problem the cox texaco engine use large props with no problem castor oil is what this engines need
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Old Jan 19, 2008, 01:22 PM
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Joined Dec 2007
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I have some old Cox 049s. They run on 10% nitro but seem to rpefer 15% and up. I have trouble gettign pure coastor fuel and, lordy, does it make a sticky mess. I use a 15% nitro, 18% synthetic blend with 2 tbsp castor per quart.

Seems to work fine.

Use that in all my engines BTW including my 16,000 rpm Wankel. Willie Wankel scream his head off but the seals have held for years. (Note the Wankel is geared internally and gets three impulses per rotation so the rotor is turning only about 5,300 when the prop goes 16k.)

Tom
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Old Jan 20, 2008, 02:06 PM
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Luebeck Blanqensee, Germany
Joined Aug 2004
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Hi all!

Many thanks for your answers!
I will try the "clean" (no notro) fuel.
I will follow Nikolashs tip.

I will post my experience here later!

Thanks to all!

Holger
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Old Jan 20, 2008, 04:56 PM
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Runcorn,Cheshire,UK
Joined Nov 2005
76 Posts
With no nitro, you will find the engine very hard to start, running backwards and it will stop in the air, they just wont run well with no nitro

Even on 16% nitro fuels they arent exactly happy i always found 25% nitro the best for the 049 sizes , .020s and 010s i always used more like 40-60% nitro

The other thing was that i found them more reliable with 22-25% castor oil than 20%, the needle was easier to set
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Old Jan 22, 2008, 04:10 PM
Rusty Joe
Fort Wayne, IN
Joined Feb 2006
34 Posts
Cox fuel

I have used 5% fuel for two years now with Cox .049 engines in SAM 1/2A endurance flights for the past two years. This contest lets the small tank of fuel to fly as long as the engine will run. About 4 mins. with a 8x3.8 electrical prop. Runs great the whole time.
Quote:
Originally Posted by holgerz
Hello!

I bought 2 Cox shure start engines.
Itís hard to buy the Cox fuel here in germany. You canít get it here. I donít know why.

I read that the Cox Engines need pure castor oil fot the lubrication.
Nearly 100% ;o) of the fuel is made with synthetic oil.

Original Cox Sprit:
For warm days
15% Nitromethane, 20% Bakers AA degummed Castor Oil, Rest Methanol.

For cold days
30% Nitromethane, 20% Bakers AA degummed Castor Oil, Rest Methanol.
From: Larry Renger, ĄCox Guruď

My questions:
Can I use fuel with synthetic oil or do I damage the Cox?

Can I use other fuel?
Like the Fuel for the diesel engines.
A third of Ether, a third of rizinus and a third of Petroleum?
Has anyone some experiences with fuel like this?
Please have in mind: I donít have dieselcylinder-head for the cox!

I want to replace the nitromethane by another liqiud. Ether (aether) is maybe a possibility, I think. It is also hard to buy nitromethane here in germany Ö

Thanks for helping!

Holger
From Germany
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Old Jan 26, 2008, 10:54 AM
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Joined Jan 2008
538 Posts
I fly my .09s, .049s, and .010s on Sig 1/2A 25% fuel. It's a 50/50 synthetic/castor blend so another small shot of castor to the quart probably doesn't hurt it. Been buying it from Tower. I fly for sport only, no competition stuff and just use a single Cox head gasket in my engines. Everything starts and runs fine without signs of wear to the piston socket. So far, so good.
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Old Jan 30, 2008, 03:38 AM
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jcervantes11's Avatar
Joined Sep 2003
1,412 Posts
I use 33 percent traxxas racing fuel on my cox engine. My hyper viper
sure start engine pull pretty good. Also one of my fomies flies good
with that fuel. Just extra cleaning needed LOL. It tend to release alot
of lubrication. I've used it for couple months and throughout last
summer, not bad still pulls great and doesn't over heat that much.
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