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Cox Engine of The Month
February-2024
1/2A Nut's

"RC Speed Boat Power Drive TD .020"

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020 troubleshooting Empty 020 troubleshooting

Post  Grf4413 Fri May 12, 2023 12:59 pm

Bench ran a couple of 020's.  Both lost rpm's when I removed the glow clip. Guessing 2 to 4 thousand rpm.  Played with needle valve, but couldn't get the rpm's back. Running a 4x3 prop, and Sig champion 20% nitro. Anyone with ideas would be a great help. My thoughts , glow plug or need a little higher nitro %. Thnaks
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Post  GallopingGhostler Fri May 12, 2023 3:06 pm

Grf4413 wrote:Bench ran a couple of 020's.  Both lost rpm's when I removed the glow clip. Guessing 2 to 4 thousand rpm.  Played with needle valve, but couldn't get the rpm's back. Running a 4x3 prop, and Sig champion 20% nitro. Anyone with ideas would be a great help. My thoughts , glow plug or need a little higher nitro %. Thnaks
This is a sure sign that the glow head is going bad. There is a rare earth coating of either platinum or iridium or combination of both on the nichrome wire element. The coating acts as a catalyst to keep the nichrome wire hot, when it comes in contact with the methanol in the fuel. If wire looks intact (not flaky or ash like), chances are that has happened. If the coating degrades, then the catalytic action diminishes, causing that drop in RPM.

That is why with the battery attached, the nichrome element is red hot causing excellent RPM, but with it removed, the nichrome wire temperature drops because the coating can't keep the wire hot, causing RPM drop after ignition wires are removed.

Fortunately, Cox International (Bernie) and Ex Model Engines (Matt) have .020 glow heads available.

Just for sake of discussion, back about 10 years ago, I bought a whole card of 10 or 12 Swanson Associates Fireball red hot glow plugs. They would work for a couple days, then do exactly what you describe on my larger engines. After research, I found out that there was a period of time, maybe 30 years ago, in which Swanson had received defectively coated nichrome wire for their plugs. Fortunately, I did not lose a whole lot of money, because then one could get a card of glow plugs for under $30.

Yet, an old Enya #30 plug that came with a used 1965 model .09-III TV worked flawlessly, which goes to show that age is not a factor affecting the quality of plugs.
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Post  rdw777 Fri May 12, 2023 5:00 pm

That’s great advice focusing on the glow head on this issue…. Also, make sure you’re not leaking from the head/cylinder joint or the post itself on the glow head… You can use some castor oil brushed on an turn it over thru compression to check…. Leveling the bottom of the head with very fine sandpaper (400 or better) and a new copper head gasket can help seal….
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Post  Grf4413 Fri May 12, 2023 9:27 pm

Thanks for the good explanation. After I read it , it makes sense to me. Just to keep going, are 020's happy with 20% nitro, or do they like a little more?? Thanks again!!!
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Post  GallopingGhostler Fri May 12, 2023 10:59 pm

Grf4413 wrote:Thanks for the good explanation. After I read it , it makes sense to me.  Just to keep going, are 020's happy with 20% nitro, or do they like a little more??  Thanks again!!!
20% nitro is fine. Cox fuel of the day was 15% nitro. Main thing is 20% oil package with at least half as Castor oil. Castor oil has a higher heat of vaporization, combusts at a higher temperature than synthetic, so if you have a lean run where there is less oil to lubricate the engine internals, it persists on internal surfaces to include the sensitive piston ball and socket joint for the connecting rod and the aluminum crankcase bearing surfaces.

Back in the day some 50 years ago, I was doing a lot of .020 Pee Wee flying single channel R/C. Because the Cox fuels were not available at the military bases where I lived in the barracks and flew, I usually used K&B Supersonic 1000 and Duke's Missile Mist. These are 25% nitro. Later in college in the late 1970's, was buying SIG Champion 25% nitro fuel with 20% Castor oil.
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Legacy fuel data from MECOA website.

Somehow I feel that the formulas in MECOA's proposed fuel manufacturing, for the K&B differs from the stuff back then, because I was devarnishing my Pee Wee's every couple hundred flights, which must have been nearly all Castor. Synthetic oil helps to keep the varnishing effect down, not good for the old worn out legacy engines like the Fox, Testor McCoy Red Head, K&B Torpedo soft steel cylinders with iron pistons.

Fuels back then were mostly Castor with may be a couple percent other "secret" formula and a minimum 20% oil. (Some thought may be Acetone to keep Castor suspended).
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