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Cox Engine of The Month
December-2018
Dave P.'s

"RC Tee Dee 049"



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cox 049 gasoline

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Re: cox 049 gasoline

Post  crankbndr on Fri Jan 04, 2019 1:39 pm

Towards the end of the spark era Dooling recommended castor and methanol and Im sure nitro and other chemicals were tried.
The racers were blowing these up with exotic fuels. I read the early gas sparkers used gas and 90 W oil.




This is a spec sheet for the Dooling



Another guy named Underwood set out to strengthen the crankcase and made the Yellowjackets, these are rare and very collectable. Mine is a repro from Woody Bartelt.
The Dooling parts would fit the new case.
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Re: cox 049 gasoline

Post  wmazz on Thu Jan 10, 2019 9:15 pm

GallopingGhostler wrote:
Gasoline has a higher heating value than Methanol. It would be more economical as one doesn't need to carry as much fuel as they would with glow.

The prospects seem promising

That is certainly the up side, but rc gasoline conversions are hard on the con-rod
bearing. An RC car manufacture sells a gasoline conversion (~.32) and it uses a
roller bearing on the connecting rod to prevent failures.


Bill M.

I wonder if leaded gasoline made small engines more reliable?
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Re: cox 049 gasoline

Post  GallopingGhostler on Fri Jan 11, 2019 6:04 am

wmazz wrote:
GallopingGhostler wrote:Gasoline has a higher heating value than Methanol. It would be more economical as one doesn't need to carry as much fuel as they would with glow. The prospects seem promising
That is certainly the up side, but rc gasoline conversions are hard on the con-rod bearing. An RC car manufacture sells a gasoline conversion (~.32) and it uses a roller bearing on the connecting rod to prevent failures.

You have a point there, Bill, something I hadn't considered in my statement, and there is a scientific reason behind that con-rod bearing failure.

SMOKEmUP: Fuel Comparison: Gasoline, Methanol, Nitromethane

Gasoline has an air fuel ratio of 12.8:1. Methanol has an air fuel ratio of 6.0:1. This is why one gets a longer run time with gasoline over methanol. Roughly twice as much methanol is required to maintain combustion. Even if one retains the same 2 cycle oil (Castor/Synth) quantities, during the 2 cycle combustion, that fuel oil mixture is roughly halved, meaning that the interior bearing surfaces receive roughly half the oil that they would normally get with methanol.

I wonder if leaded gasoline made small engines more reliable?

Over time, gleaning from various automotive magazine articles, lead in the fuel, besides being an anti-pre-ignition knock agent, lubricated the valve seats and valve face that contacted the valve seat. Without required going to hardened valve seats and valves. This also went for 4 cycle small engines that didn't mix oil with the fuel for lubrication.

If it benefited 2 cycle small engines? It could be possible there was, but with oil already in the fuel for lubrication, appears that any additional benefit was probably minimal, except that in the case of high compression engines helped to prevent pre-detonation.

The 1934 Brown Junior 10 cc (0.60 cu.in.) petrol engine had a compression ratio of 6.5:1, and as such it was preferred to run on white (unleaded) gas due to its low compression ratio not requiring octane boosting.

Your thoughts? - George
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Re: cox 049 gasoline

Post  wmazz on Fri Jan 11, 2019 10:33 pm

Nothing scientific to add, but I have first hand experience with the NGH 9cc RC gasoline engine.
I participated in a long thread @rcgroups. I was initially interested in the NGH because it used
a version of a float diaphragm carb similar to what Watercraft carbs from SeaDoo's and JetSki
used, but also similar the Walbro carbs I used on GoPeds and RC Zenoah. In fact the pump and
diaphragm used Walbro parts.  

Besides the carburetor problems, connecting rod bearings failed. There was talk about oil ratio,
and some people ran oil ratio similar to larger engines. But the owner of NGH thought it was caused
by the engine leaning out, possibly while someone was tuning the carb for peak performance.

Since then I have watched other companies produce miniature gasoline engines like the 1/8 RC
car/buggy. It showed up in a few model shows, but its release took a couple of years, and resulted
in a roller bearing connecting rod and a plug cap integrated into the tall cylinder head.


Bill M.
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Re: cox 049 gasoline

Post  GallopingGhostler on Sat Jan 12, 2019 12:02 am

Bill, being curious, I took a look at the engine manual for the Evolution 10GX 10cc Gas Engine with Pumped Carburetor (EVOE10GX2).

Horizon Hobby: EVOE10GX2-Manual-EN.pdf

Towards the back is the exploded parts diagram, surely enough the lower end of the conrod assembly has a removable bearing. Whether it is a ball bearing or bronze one, that I can't tell from the diagram, but usually bronze bearings are pressed in and not considered as user serviceable and usually not shown on parts diagrams, so it is probably a ball bearing.

The Brown Jr. used a fuel oil ratio of 3:1. Oil was 60W mineral oil. Its conrod has bronze bearings. Both the Evolution and NGH use a 20:1 fuel oil ratio, oil being 2 cycle oil.

Don't have any experience on these very little gassers for model aircraft, so I can't speak from experience. I'm wondering if one were to use Castor oil as significant component in the oil mix might have helped to prevent conrod bearing failure in the NGH 9 cc. Don't know if having some Castor content may gum up the carburettor.

If there is better success with the 10GX, it would seem than for only $60 more might be a better engine. Again, I haven't really kept up with these engines.

I did notice though that Horizon is offering the 8 cc Evolution gasser, which is a touch smaller than the NGH.

At one time, Hobby King had the NGH 9 cc on sale for a touch over $100. Since you mentioned about conrod bearing problems gives me a sense of relief for not jumping onto the band wagon.
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Re: cox 049 gasoline

Post  robot797 on Sat Jan 12, 2019 3:14 pm

cant the lac of oil be solved with more oil
like I use 20% oil right now
but if I were to use 40%
I get more lubrication and I have to open the needle a bit

I see only pro's (and one con with that methode)
finer control over fuel (I only have half a turn right now and its twitchy)
more lubrication
heat gets removed quicker (with the unburned oil)
the con is the fuel tank get emptyed faster


ps I found a use for the conversion
it will be build onto a 80 car (to bad it aint a cox car)
and it will be something to brag with
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Re: cox 049 gasoline

Post  wmazz on Sun Jan 13, 2019 2:33 am

The NGH had tuning constancy problems too. The first engines used
exhaust pressure, but that led the engineer to use a modified Walbro
carb to supply fuel. But that set-up had problems keeping the needle
and seat open.

Perhaps a finer tapered needle valve. The original Cox needle was designed
for nearly twice the fuel flow compared to gasoline. A smaller diameter
venturi may help too.

For any of my high performance engines, I like using a rich oil ratio, and
I prefer the fortified castor Maxima sells as "927."


Bill M.

I don't know what 20% oil is like, we use ~5% on the racing engines and
the NGH. Perhaps 6 to 7% maybe a better starting point.
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Re: cox 049 gasoline

Post  gkamysz on Sun Jan 13, 2019 9:56 am

40% oil is excessive. Is there evidence of problems at 20%? Oil doesn't cool the engine significantly. Adding castor won't save a rod bearing, unless the oil you are using has extremely low viscosity. I fine thread needle would certainly help here. I don't know enough about which horseshoe backplates have them, but I have a couple with the 128tpi needle.

NGH9 has a lot of problems overall. I got a blown one to see what the problems were. The crankshaft heat treat is bad. The original and spare were both soft. This wouldn't cause immediate big end failure, but longevity is questionable. I just don't have much to day about poorly developed and built engines.
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Re: cox 049 gasoline

Post  robot797 on Sun Jan 13, 2019 1:09 pm

well currently
I only have a problem with the fuel supply when I wanna run the engine rich
it wobbles between flooded and not flooded
so the needle is good enough for high rpm
and I am thinking of extra oil just as a precausion
(also I mix synthetic and organic oil that is why i think the oil will pull some heat away)
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Re: cox 049 gasoline

Post  gkamysz on Sun Jan 13, 2019 1:15 pm

As long as the needle is allowing you to tune it where you want it. At very rich settings, factors other than the needle itself come into play.

If you calculate how much heat the oil can carry away, vs. total heat input from burning fuel, you'll see it's negligible.
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Re: cox 049 gasoline

Post  robot797 on Sun Jan 13, 2019 1:44 pm

true true
but even then themore lube the better XD
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Re: cox 049 gasoline

Post  gkamysz on Sun Jan 13, 2019 2:49 pm

At some point you're just throwing money, even if it's pennies in this case, through the exhaust.
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Re: cox 049 gasoline

Post  robot797 on Sun Jan 13, 2019 2:59 pm

Very Happy
gasoline is like 10 times cheaper as nitro
i dont mind trowing pennies away
if it means the engine runs better and longer
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Re: cox 049 gasoline

Post  GallopingGhostler on Sun Jan 13, 2019 7:34 pm

Regarding 40% oil content, somewhere I read, it may have even been the well known engine tester Peter Chinn, (or Paul Gilbeaut?) that the practical limits on oil content (all Castor) was 25%. This was due to the small passageways in the fuel system, couldn't handle the thicker viscosities of the fuel oil mix well.

Greatest concern in the Cox engines has always been maintaining adequate lubrication of the ball and socket joint for the con rod piston end. It is below the hottest area of the piston where combustion occurs. Castor has a higher flashpoint, doesn't vaporize as readily as synthetic oil.

If Castor can keep this socket joint lubricated, I can't see why it can't do the same for the lower con rod end at the crankshaft.

You do have one advantage to attempting this experiment on a Cox engine. Parts are relatively cheap and available, so if excessive wear occurs, it is easy to fix. Since I know of no one else attempting this experiment, you're developing valuable experience that can be shared with others, if they decide to do so.

Going to all Castor 20% to 25% may be a way to go with gasoline? With oil basically cut in half due to the greater stoichiometric efficiency of gasoline and increased heat while running, using all Castor seems to have merit, no?
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Re: cox 049 gasoline

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