Strange Glow Plug Behavior.
 

I've had 4 to 5 glow plugs go bad in about 10 flights on a pair of os 35fp. The plug looks normal . The coil is not distorted. It glows with the igniter . The engine starts and runs at higher speed but stops at idle. Put a new plug in and things are fine again. I'm use a os #8 plug. What's causing this to happen? Should I be using a different plug for this engine.

Most likely bad fuel, not a plug problem.

Or possibly a carb adjustment, even though the plug change seems to help breifly.

The nickel coating might be falling off from the cylinder walls and alloy with the platinum wire, thus fouling the plugs.

could the plugs be OS Clones ?? I have heard they are out there

Jim

I've made 8 good flights now. Changed props from 9x6 apc to 9x5 ma . Runs good at high speed and idles good.

yee-up, it makes since, your engines are revving higher, so your RPM is more in sync with the #8 plug, I'm betting a slightly hotter plug would work with the 9x6, cause it would start the flame front earlier

Jim

The #8 plug is usually a safe bet for most engines even when it isn't the best choice.

So, the OS 8 has worked OK and then not?
What changed to cause the problem??
Most likely is fuel, but we're in the dark without more info

Could also be platinum, iridium or other rare earth metal coating on the plug's heating wire, which cause the catalystic reaction with glow fuel has deteriorated.

I had a half dozen NOS Swanson Associates Fireball plugs go bad on me in short order. I pull out a new plug, fly a couple days, then lay off for a week or two, the plugs would no longer sustain ignition, just pop and sputter. Replace with a new one fixed the problem until it went bad in short order. :o

Got word some time back about 20 years ago, they had been supplied defective wire for their plugs. The NOS card lot I bought some time ago were all bad. :mad:

Try a different brand plug that is known to work. If it does and solves the problem, could be you bought a bad lot of plugs somewhere. :)

:confused: :rolleyes: ;)

Actually, I was concurring with you. Overall, OS has done well with their engines, but a few times there have quality control issues here and there, like the FP's with cylinder nickel plating flaking off some time back.

But in true reality, it's the Enya's that are solid platinum. ;) ;) ;)

Really, whatever plug makes the engine run best is the right plug for that engine. A persons flying style sometimes has effect on the perceived quality of a glow plug. I believe the major thing to keep in mind is to remain open minded if having problems finding the 'right' glow plug.

of course, but you also have to add the fact that an engine may not be "prop loaded" correctly for the plug in use, some people just don't understand that, I have seen it, LOL now lets talk about plug quality, I have read in the forums that there are some "OS 8" clones on the market,

2 examples of incorrectly loaded engines,
1) this guy had a Magnum 160 Twin 4St, he was complaining his engine would flame out at times when adding power and or just before lift off, I asked if I could throw in my $.002 and he said no, 5 minutes later he asked me, so I asked what prop he had on his engine, well, my god, a super light Zinger 13X4 is just too small to load a 160 4St correctly, I sold him an APC 15X8 for $7 (the only prop at the field at that moment that was close to what he needed, he should have had a 16X7 or 8 on it), he mounted the 15x8 and that problem was solved in that instant,,
20 minutes later we was complaining that his engine (the same engine) would stal at times as he come's off the power in flight or to land, and with his sharp way he asked me if I had anything to say about that problem, well I asked what brand plugs, and what ## plugs he was using, he was using TT 4St plugs, I told him he should be using a better brand such as OS,, at that he said "Prop this Plug that",,,,,,,, 2 weeks later he came back and said he swapped to OS plugs and his engine had not stalled since he went to the OS plugs..

2) I watched a friend work on his plane for 3 hours, 3 hours of tuning and swapping plugs, swapping from OS 8 to Enya 3, his engine too, would stall at full throttle every time just before lift off, he could not get the plane off the ground.. well I kept my mouth shut because of the guy in my first story above, I just didn't want to stick my nose in, some people do not like that,, but after 3 hours I finely asked if I could help,, well I knew what the problem was,, the engine was a 61, and he had a super light Zinger 9X4 on it, I told him that a 61 needed a 12x6 or at-least an 11x8, he said "he had a 12x6 on it and it ran good" so he swapped to a 12x6, once he changed to an APC 12X6, again, his problem was instantly gone.

as Dirty Harry would say "an engine has got to know it's limitations"

Jim

Well, the FP engines still have that problem and the engine in question here is indeed an FP. That's why I suggested earlier that the nickel can foul the plug. It is just a matter of lifting the head to take a peak inside, a 5 minutes job... ;)

What's the best way to choose the proper prop size for a glow engine . I'm a sport flyer loops , rolls, split s, and some inverted flight. I usually load the engine light to keep the rpm up. Maybe this is not the best for the engine?

what engine, and muffler