Glow plug fouling with Sig Champion fuel-can't fly

What kind of battery are you using? Even the larger Hobbico 1.5 F cell hobby battery works far superior when ganged using 2 of them. If your using 1.5 dry cells D cells, I would gang a minimum of 4. Cox plugs are extremely hard on batteries and they need a good power source. A stock Cox glow plug clip is not a good clip to use. The wires are too small and the resistance it creates shortens battery life and also doesn't make the plug glow brightly. In other words, your plug might be glowing good enough when you look at it initially, but a minute or two later it's not so good. When I suggest multiple batteries, don't wire them so that the voltage obviously increases rather to keep them at 1.5 volts, think of it as a larger tank so to speak. Engines that are hard to start initially can taxi battery life quickly. If these are your original plugs from years back, replace them as they will serve you better more than likely and it takes the guess work out. It sounds like they're caked with castor goo. It will burn out but it certainly becomes more demanding on starts and those plugs could also quickly let you down when you least expect it. Ken

Thanks for the replies.
Further clarification..
The engine is a Cox .020 Tee Dee with a standard cox glow plug head, one gasket. Before that same issues with a trusty old Black Widow Yes, I understand I can go with multiple batteries, I will do that too. All of the Cox engines were stored in a dry place-in storage boxes, each run dry and put away with after run oil used. Tests stand is the Cox International blue alloy test stand. All starting instructions on engine start were followed. Sig Champion 25% fuel.
Taking photos now and figuring how to post.

In my opinion an engine that sat for a lone time (even never run) should be taken apart and cleaned, after that a process of elimination new head,batteries, fuel.

Hello helpful Cox friends,
You can see all of the items I use to start the engines on my gallery photo--PT19. Yes, I completely went thru the all of the Cox engines before attempting to start. the plastic back plate on the Cox TD .020 had separated so I repaired that. The facts are, a perfectly good silver glow coil went from silver to black ( in 20 minutes or so of attempting to start) with starting procedure that I have used for years. Cox clip, new sig champion 25% nitro fuel, new 1.5 volt battery. It might be the fuel, yet I have not had this happen before. The fuel I used before was Byron 25% nitro. I have now blackened 4 X glow plugs, 2 x .020 and 2 X .049 baby bee/black widow glow plugs. I have never experienced this before and I have been starting and flying Cox engines since the 70's. I wonder if the Hobbico after run oil is to blame? All of these engines were put away with this lubing them to prevent moisture and rust. I have ordered new glow plugs, but this has become frustrating and expensive--glow plugs cost a bit, and are getting scarce--as you all know. How to clean the coils of the glow plug--denatured alcohol did not work. Perhaps there is a acid that will clean the coil--perhaps Tarnex will help??--I know it is an acid and cleans other metals...
I have read all I can find about this, but no luck....
Thank you

I 've pulled apart many and some the cranks are discolored and need polishing and the bore needs a good cleaning also, don't think bad fuel would turn glowhead black.
I've had luck in the past cleaning glow heads with this, but they weren't black

PT19 wrote:  I wonder if the Hobbico after run oil is to blame?  

Its the first ting I thought of when you explained how they were stored .... might be a good consideration.

I recently cleaned up a bunch of really old glow heads with Hoppes bore cleaner. Let them soak over night and then burned off all the residue with the glow clip. I use the black one, btw, and not that cheap-o yellow clip. Never had good luck with that.

Hope you get it sorted out ....

Even if the coils are blackened with contamination, I don't see why they still wouldn't reach the same temperature when connected to a good battery. The resistance won't have changed due to anything stuck on the outside. What may happen is that the plug may not continue to glow after the battery is removed once running, but with it connected the plugs should still produce the same amount of heat to be able to fire it up and run as normal. I really think it has to be a weak battery or poor connection. If they all glow bright, then it has to be bad fuel for all the engines to react the same.

I think that even if the coil glows, if the contamination blankets the platinum coating and keeps it from coming into contact with the methanol, this plug may be toast. The action is purely catalytic and uses heat only to initiate ignition. After starting, catalysis keeps the plug hot, not exclusively engine heat. If he can't return it to a clean condition, it's time for a new plug; even if it appears clean, the platinum may be eroded away.

Oldenginerod wrote:.... The resistance won't have changed due to anything stuck on the outside....

Not necessarily. If it's contiguous and covering most of the element, it has a conductivity value of its own, in parallel with the metal coil. If it's carbon, it may be more conductive and soaking the battery even worse. And as mentioned, blocking the platinum from the methanol which keeps it lit.

Sorry, though, I don't have any better idea than solids cooked out of the after run oil. For future storage, air tool oil is the cleanest stuff that I've heard of.
Rusty

Some air tool oils are "nonflammable" and will not burn away causing problems.

Phil

My .. I use a power-panel's glow-driver with the regular Cox yellow clip and leads, connected to the glow-driver output. To power the 12V panel; I connect two (2) 6V lantern batteries in series. I don't run any other accessories off the panel. The two batteries deliver plenty of amperage for the glow-driver. Cox had a starting battery that was comprised of 4 D-cells in parallel. It was a decent little battery.. and lasted quite a while, once you got the knack of getting your engine started in short order.

I like the power-panel and lantern batteries because it basically delivers the amperage of 8 D-cells to the glow-driver circuit.. which is adjustable for current and has a meter for measuring output. A meter can also help diagnose an open connection/bad plug. If the meter's in the green when connected to your plug.. it's glowing hot.. and you can hear an exhaust-prime sizzle.

I made a 6" x 6" box (inside measurements) 4" deep.. which fits a standard Hobbico/Tower power-panel and 2 lantern batteries.. with room for a quart of fuel, spare props, tools.. For me; it's a reliable, lightweight and compact tote for 1/2A flying. The lantern batteries aren't cheap or rechargeable.. but they'll last a lot longer than a 3 or 4 D-cell pack.. and you don't need to build a box with contacts. I just use one short jumper-wire with clips to bridge the two lantern batteries in series (+/-).

Dang, Roddie, I wish you lived in my neighborhood. I sweated bullets today, just making a properly shaped firewall out of one flat piece of plywood. I'm such an inept carpenter.

Thank you to all that have replied.
I have cleaned the contacts on the older cox glow plug clip ( 20 years old) and have found this needs replacing--new one on order and I will follow all of the great suggestions on heavier wire to a better clip along with better battery power. I have ordered new glow plugs, for .020 tee dees and .049 engines. Yes, something has coated the coils of the glow plug and caused the blackening--still not sure of the cause. Yes, these were older glow plugs--honestly 20 years old on some--yet the were stored well and look good...Hard to believe how time gets away from you. The under powering of the voltage to the coil could be the cause? With better power supply and new glow plugs I will carefully rebuild the fleet of engines and work hard to get them serviceable again. I have many favorite small planes and kits anxious to fly again.

PT19 wrote:Thank you to all that have replied.
... Yes, these were older glow plugs--honestly 20 years old on some--yet the were stored well and look good...Hard to believe how time gets away from you. The under powering of the voltage to the coil could be the cause?  With better power supply and new glow plugs I will carefully rebuild the fleet of engines and work hard to get them serviceable again. I have many favorite small planes and kits anxious to fly again.

You're quite welcome PT, that's what we do here. When I dusted off the few parts I had, I was using some plugs that must've been older than that. We may never know. But if you clean everything up, oil it with fresh clear oil, and get your starters up to par, i think it will all work fine. If your first new plug suffers the same fate, Stop! Let us know. Maybe it turns out to be the fuel. But I really doubt it, not turning them black.

I haven't mentioned it, but if you ever use a spring-clip type 2-D battery box, get one with copper plated leaf springs. I have had one with the chrome steel springs and soldered the leads right to the base of the spring, and it still wouldn't light a plug. I have found rechargeable batteries give you more consecutive brightly lit starts in a row than alkalines, which die off gradually with each start. And of course copper wire is superior too. CLEAN, SOLDERED, TIGHT, COPPER.

These glow plugs are surprisingly demanding current hogs. Not too far from a short circuit.

Good luck.
Rusty

Some contaminates coat the glow plug element and can not be removed. You will notice these cases after you have started and adjusted your engine. When you remove the glow plug clip you will experience a drop in RPM or it may even stop. This problem is caused by the contaminate preventing full catalytic reaction between the alcohol in the fuel and the platinum in the glow plug element.

In these cases you may be able to use them initially while you are bench running your engine, then replace them for flying, or discard them. I prefer to just discard them. If you decide to keep them, be sure to mark them and keep them separated from the good plugs.

George

Hello Cox engine friends..
I hate to tell everyone--but this morning I rebuilt another of my Cox .020 tee Dee and tried again to fire it up. After several minutes of no starting (same glow plug smoldering issues) I decided to go over to the "dark side." I put two D cell batteries to it--3 volts--and low and behold it fired right up and ran great. I know what everyone will say--I will burn out the glow plug--but I was careful to only have it on the plug for a very short time. I got a bright glow and it seamed to burn off whatever was on the coils of the plugs--tried two different plugs. the Sig Champion 25% nitro fuel worked fine--so that appears to eliminate that as a problem...so far...

I ran the tee dee .020 several times this morning mounted back on the front of the Ken Willard School Boy--I will send photos of this in flight and completed with new lightweight 2.4gHz radio. I will get new plugs (on order), rebuild all .020 & .049 engines and proceed with a better plug clip and heavier wire for starting. Hopefully I will get all of my engines back running and get several half-A planes back in the air with lightweight and non-interfering radios. More photos to follow.