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Author Topic: Fuel for old engines  (Read 546 times)
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alfakilo
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« on: March 11, 2022, 10:41:43 AM »

I'm thinking about getting my engines from the 50s up and running...everything from Cox 020/049 to Fox and Torpedo 23, 29. and 35s. I'm concerned about running modern fuels in them. How should I modify a typical hobby shop fuel to keep from possibly damaging these engines?
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strat-o
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« Reply #1 on: March 11, 2022, 11:21:59 AM »

I think the only two factors you have to be concerned about is Nitro content (%) and lubrication content.  I think that lubrication content, like castor oil, is fairly standard over the years.  The nitro content can vary by a lot from zero to ...?  So maybe the question is, what is the optimal nitro content for these engines?
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Pit
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« Reply #2 on: March 14, 2022, 03:02:36 PM »

Older engines, like Fox and others manufactured prior to about 1976 need more lubrication than the modern fuels provide due to the metallurgy.  IIRC, Fox in particular recommended a minimum of 20-22% or even up to 25% castor.

Modern fuels are usually in the 16 to 18%, but can generally be special ordered with higher oil content (not generally found in any brick & mortar HS -if you can find such a shop).  De-gummed castor oil can be added to most current fuels or maybe some manufacturers can supply the specific oils that they use - which brings us back to just ordering what you need...

Small engines, like the Cox family, thrive on LOTS of nitro !  15% is about the minimum for general reliability for Babe Bee's and such, but the higher output models (Black Widows, Medallions and TeeDee's) need a higher nitro content to be happy.

Konrad, your motor expertise is needed!

Pete
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ffkiwi
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« Reply #3 on: March 14, 2022, 03:38:13 PM »

The simple answer is: older engines NEED castor-and plenty of it-simply due to the metallurgy-which is invariably ferrous-ie leaded steel or cast iron piston running in a steel cylinder or liner....one of the pair normally hardened (usually...but not exclusively, the cylinder)-or an aluminium piston with reasonable clearance fitted with one or more compression rings....that pretty much covers all the options for the 50's era.  Firstly-unless they are all new and unrun-they will have been run on a castor based fuel-so will have a degree of castor residue on the working surfaces-in quite a lot of cases that actually contributes to the compression seal...glows of that era being set up fairly 'loose' in terms of clearance.  Running these on modern fuels which are invariably based on synthetic lubricants (unless specifically ordered as a castor lubricant fuel-which some suppliers do still offer) will strip the castor layer from the working parts as synthetic oils have a detergent action in use-which may well result in your engine losing compression and being harder to start....depending on how it was set up, clearance wise,  in the first place.

If you're cautious by nature-then go with all castor fuel-but for most purposes, a fuel with at least half the lubricant content being castor is probably adequate for most uses.....and this is where it gets a bit messy-there is a vast array of fuels on the market-designed for a wide range of uses and engines-car fuels, 1/2A fuels, heli fuels-the demands of the various usages require in many cases significantly different formulations-and -the critical component as far as old engines are concerned is the amount of lubricant-and this could be as low as 12% or even less  in some car fuels-and disastrous for your engines if used just as supplied. Most modern 'aero' as distinct from 'car' fuels are a bit better off-lubricant levels being around the 18% mark-which is still a bit low for older engines-and again usually synthetic-though some may have a small proportion of the overall lubricant component as castor.

You have in practice three choices: make up your own fuel to a typical blend of the day-typically 20% castor and whatever nitro % you'r comfortable with, or buy a commercial fuel that is stated as castor lube. the third option is to buy an existing fuel and add castor to it to bring up the overall lubricant % and ensure there is a decent level of castor for your older engines to be comfortable with. This obviously involves a bit of work, calculating % etc-but there are calculators on line which can do the work for you, if you input the various components and what you want the final mix to be. needless to say-if you're adding castor to an existing premixed fuel blend-you will be diluting the other components when you do-so if for example you wanted a 5% nitro mix at the end, you would need to start with a higher nitro% fuel to account for the dilution factor. [and what you might need to start with might not be commercially available-but the calculators will usually handle a range of inputs and tell you what to add to reach your desired endstate.

 In your shoes I'd go for at least 20% lubricant-with half of it castor, and 10% nitro which the Torps should be happy on-the Coxes might like a little more nitro-especially the 020s. You can find the formulae for the cox fuel blends on line, should you wish to duplicate them (there were three different Cox blends, from memory)

 ChrisM
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alfakilo
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« Reply #4 on: March 15, 2022, 03:38:24 PM »

The simple answer is....

Thanks, Chris! Great post and exactly the info I am looking for.
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flydean1
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« Reply #5 on: March 15, 2022, 04:08:02 PM »

Not being the calculating type, I settled on a "standard" mix for my plain-bearing mostly Nostalgia Gas engines.

I use a translucent straight-sided container which is over 10 inches tall.  Measuring to 10 inches, and making a mark at 9-1/2 inches as well gives me my mix.

I purchase commercial 40% nitro fuel (Morgan or Red Max) which has 20% lube and half castor.  Then I fill my mixing container to 9-1/2 with the commercial fuel, then add castor to bring it up to 10 inches.

I use that for everything including 1/2A's.  For the very few ball bearing ABC or AAC engines I use the 40% straight.

My "big" engines are largely OS MAX-III in .19, .29, & .35 sizes.  I do have a small amount of 65% for a couple 1/2A's that are set up for the higher nitro.

Hope this helps.
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Ployd
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« Reply #6 on: March 15, 2022, 09:40:15 PM »

Cox fuel mix.
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alfakilo
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« Reply #7 on: March 16, 2022, 08:58:47 AM »

Not being the calculating type, I settled on a "standard" mix for my plain-bearing mostly Nostalgia Gas engines...Hope this helps.

Well it certainly appeals to my decidedly non-math mind!!

What does the oil % end up as?
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flydean1
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« Reply #8 on: March 16, 2022, 12:44:39 PM »

I think the oil winds up at 22% +/_ over half which is castor.  Again, not good at calcs.
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bsadonkill
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« Reply #9 on: March 18, 2022, 08:07:06 AM »

You can check out Brodak Manufacturing online. They may have what you need. Wink
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ghostler
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« Reply #10 on: March 18, 2022, 08:16:26 PM »

Formula appears to be while LM Cox company was still in business. Leroy lost his shirt when the slot market craze hit and he geared up immensely, then it crashed sometime around 1967. He had large inventories of unsold slot car gear, lost his shirt, sold the company to Leisure Dynamics. A partial history is available at:

https://www.modelaircraft.org/sites/default/files/CoxLeroyM.pdf

That 30% nitro formula, oil is 20% with 18% as Castor, 2% as Klotz KL201, a synthetic. Not too far back may be 7 or 8 years ago, O'Donnell Fuels purchased by Hobbico/Tower Hobbies, advertised Cox Fuel. However, they were simply rebranding their normal RC fuel. Then Bernie of Cox International, Canada contacted them directly, telling them their mix of 2% Castor and 16% synthetic was wrong, would not protect the ball and socket joint of the connecting rod in the piston. (Nor, it would be good for the steel crankshaft running in the aluminum extruded crankcase, no bronze bearings there.) They revised their formula to 10% Castor, 10% synthetic for a 20% oil package.

This is the current recommendation. Someone did some extensive research may be 10 years ago, I don't know where, probably died somewhere in the Internet rabbit hole. He found that for the old plain bearing cross scavenged engines, that the absolute minimum Castor oil content that would help to protect an overheating condition was 6% Castor.

That said, in a pinch (my nearest fuel source was 95 miles and two hour drive away and no Cox fuel in sight), I put 8 oz. Klotz Benol Racing Castor (available at some motorcycle dealers) in with a gallon of Wildcat fuel. Mix is attached. This gave me 9% Castor and 11% synth, for 20% oil total. For my legacy engines and Coxes, I have added 16 oz. (1 pint) of Benol, which gives me a 25% oil package with 14% Castor and 11% Synth. This is what I run in my CL plain bearing cross scavenge engines (Enya, Testor, etc. I don't have a Fox .35).

My Norvel .061 didn't like the heavier 25% oil package. Cox reedies seemed OK. (Peter Chinn recommended not to go above 25% oil, because the metering passages in the half-A's are too small to handle it.

Anyway, I'm not expert on this and YMMV (your mileage may vary, you are on your own). If you are concerned over 9% Castor by adding 8 oz. to a gallon, then bump it up to 10 oz to push it up to 10%. I based mine on 15% nitro, which is fine for sport use. Those with a need-for-speed will need to opt for higher nitro fuel.
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Heikki K
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« Reply #11 on: April 14, 2022, 04:08:29 AM »

I have ended to a conclusion, that vintage engines with cast iron piston (without a ring) absolutely do need castor oil. Up to 33% with the rookie type diesel engines, like Webra Record, David Andersen, Yin Yang 2,5cc and also, with Oliver. These are all the "see-thru" type engines having the exhaust ports in all direction, noisy, oily, lousy in power and ... so adorable! In my opinion, team racing and speed engines are run with less than minimum oil content in order to squeeze out the maximum power with the cost of service life. In the beginning of 70´s I remember new-type .40 -.60 size engines with cast aluminium piston and a cast iron ring appeared. We went to synthetic oils, lowering the oil content to 13...15% in volume. In control line stunt planes, our Super Tigres, HP:s, Webras, O.S. FSR series - they all worked endlessly years and years with the synthetic oil fuel.

I recall reading an article written by a retired BP chemists, an aeromodeller. He explained the feature of castor oil, especially it's oil film durability in high temperatures, where it starts to polymerize, instead of breaking, burning, making the typical "gumming". Castor oil will continue lubricate in the highest temperatures, where synthetic oil molecular chains start to break, making castor still the choice for example, racing 2-cycle engines. Therefore, one may find top quality castor-based racing oil and also, methanol soluble synthetic 2-cycle lubricant at the local dirt bike store. Ghostler mentioned one, Klotz Benol.

Vintage engines develop a brown castor oil gumming surface on their pistons, like an old-time "teflon layer". When talking about gasoline 2-cycle engines, outboards, chain saws and dirt bikes, more than adviced 2% - say 3-4% of oil makes them to sputter and maybe, not starting at all. This will not be with our vintage glow or diesel engines. I assume, that adding more castor oil can be used to make the running temperature lower. More castor, the engine developes less power and heat, and also, the oil absorbs and transports heat out of the cylinder. This way, adding a generous shot of castor oil has made my worn-out engine still usable. And my field jeans much darker...
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