Really bad crud on spark plug

Lndwarrior

Lndwarrior

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Gary
From my O-235-C1 engine. #2, bottom plug.

These were cleaned 11 months ago and about 50 hours.

The engine had been unusually hard to start the last two times so I decided to pull the plugs a month before the condition inspection.

For 10 of the last months I was running 100LL. The last month or so I started running mogas to help avoid this problem.

A few other plugs had some buildup but not as bad as this one.

Wondering if anyone has any thoughts on this excessive buildup? I've not seen anything this bad in the last 5 condition inspections.

I lean on the ground and in the air, every time. Also do a runup at engine shut down to help clear the plugs.
1000004784.jpg
 
Hard to tell from picture, but is the center electrode oval shaped?
 
Clip4 said:
Valve guide leaking oil on a bottom plug that appears to not being close to the proper gap.
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Gap was over by a couple of thousands which i fixed. It had been set properly at last condition inspection.
 
The O-235 is notorious for commonly fouled plugs. Be sure to lean it in the runup. You might have to lean it in the pattern and on approach, too, especially with carb heat on. I'd be pulling those plugs more frequently than once a year.
 
Were the plugs cleaned during 300 hours of use?
I rotate a set of clean plugs in my new engine at 150 or so hrs during a oil change.
 
Gary Ward said:
Were the plugs cleaned during 300 hours of use?
I rotate a set of clean plugs in my new engine at 150 or so hrs during a oil change.
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Yes, plugs were cleaned 11 months ago at the last condition inspection. Only flown 50 hours since then.
 
1710021330041.png

That's an REM37BY plug. They were designed for engines that fouled plugs easily, and the O-235 is famous for this. Notice that the spark gap is not fouled yet, due to the extended electrodes. That stuff there is lead fouling, from running the engine too cold and from running rich too much. You have to lean fairly aggressively. That #2 cylinder is right out front, and with improper baffling it can get too cold.
Lndwarrior said:
Gap was over by a couple of thousands which i fixed. It had been set properly at last condition inspection.
Click to expand...
That's much more than couple of thou over. That looks like at least .050", when the gap should be .016" to .018". Like so:

1710021641232.png

With a large gap, the plug might not even be firing half the time. Magnetos don't generate the huge voltages our cars do now, and too much gap means misfire, and then the plug will foul easily.

Lndwarrior said:
The engine had been unusually hard to start the last two times so I decided to pull the plugs a month before the condition inspection.
Click to expand...
O-235's are notoriously hard to start, so most of them have two impulse mags. But that huge gap sure isn't helping. If all the plugs are like that, yup. Hard starting.

When were the mags last opened for inspection?
 
Dan Thomas said:
View attachment 126477

That's an REM37BY plug. They were designed for engines that fouled plugs easily, and the O-235 is famous for this. Notice that the spark gap is not fouled yet, due to the extended electrodes. That stuff there is lead fouling, from running the engine too cold and from running rich too much. You have to lean fairly aggressively. That #2 cylinder is right out front, and with improper baffling it can get too cold.

That's much more than couple of thou over. That looks like at least .050", when the gap should be .016" to .018". Like so:

View attachment 126478

With a large gap, the plug might not even be firing half the time. Magnetos don't generate the huge voltages our cars do now, and too much gap means misfire, and then the plug will foul easily.


O-235's are notoriously hard to start, so most of them have two impulse mags. But that huge gap sure isn't helping. If all the plugs are like that, yup. Hard starting.

When were the mags last opened for inspection?
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Brand new Bendix mags two years ago. About 125 hours on them.
 
Lndwarrior said:
I lean on the ground
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LW, is it a long taxi for you after landing? The leaning; how aggressive?
I find many do not understand you can't hurt it at 1000rpm or idling, by leaning as much as possible - ie till it almost quits.
(less likely the problem if truly only one plug affected, but can't see the others.)
 
How are you doing the post flight run?

Idle Mixture correct?

How much rise?
 
Let'sgoflying! said:
LW, is it a long taxi for you after landing? The leaning; how aggressive?
I find many do not understand you can't hurt it at 1000rpm or idling, by leaning as much as possible - ie till it almost quits.
(less likely the problem if truly only one plug affected, but can't see the others.)
Click to expand...
Short taxi, small airport, my hangar is right at mid field. I lean until rpm drop. I live in a high DA area so leaning is ingrained in every phase of every flight.
 
Champion or Tempest? Sorry if I missed it, but wondering if you have some of the problematic Champions in there?
 
What’s your shutdown procedure? See https://www.lycoming.com/sites/defa...ngines%20Rated%2080_87%20Octane%20%281%29.pdf .

4. Prior to the engine shut-down, the engine speed should be maintained between 1000 and 1200 RPM un- til the operating temperatures have stabilized. At this time the engine speed should be increased to approx- imately 1800 RPM for 15 to 20 seconds, then reduced to 1000-1200 RPM and shut-down immediately using the mixture control.​

You need to get the temps up prior to shutdown so that the lead goes out in the exhaust gases.
 
That’s exactly what I was referring to.

Many flights have have a gradual reduction in power

( read as Combustion Chamber temperature) which allows lead build up.

It can get so bad that deposits on the piston will contact deposits

on the head. Lycoming has another Service item to blast the internals

with wheat or rice or similar.

An easy thing might be to increase the 1800 rpm some.

Or a little higher rpm ; leaned Of course.
 
What type of feeler gauge do you use to measure the sparkplug gap? Seeing how they're circular around the center electrode, you can't use flat feeler gauges.
 
UngaWunga said:
What type of feeler gauge do you use to measure the sparkplug gap? Seeing how they're circular around the center electrode, you can't use flat feeler gauges.
Click to expand...
Round wire feeler.
 
UngaWunga said:
What type of feeler gauge do you use to measure the sparkplug gap? Seeing how they're circular around the center electrode, you can't use flat feeler gauges.
Click to expand...
1710259496305.png

Several different sizes of retractable wires. The wire is hard music wire (piano string wire) and lasts a long time if you're careful. For the Lycoming, the specified gap is .016 to .022", but we used to gap them to .016" so that the gap never got near the .022" between plug checks. https://www.lycoming.com/sites/default/files/attachments/SI1042AH%20Approved%20Spark%20Plugs.pdf

Continental has a range of gap settings:
https://www.csobeech.com/files/TCM-SparkPlugRotation-SIL03-2B.pdf

To get the .016" gap, I would use the .015" wire. Put it in the gap and start closing the gap with a proper setting tool. Once the wire started to drag in the gap, stop closing and release the pressure on the electrode. It will spring open to about .016". Gapping any other way risks getting the gap too small, and you're not supposed to try to open it, as you could easily move the center electrode and crack the ceramic. Not only do you get spark shorting though the crack, but pieces of that insanely hard ceramic can break off and score the daylights out of the cylinder.
 
I also used Dan’s .015 method.

As mentioned stop closing when you feel drag.

IMHO it is essential to keep the feeler wire moving

to notice the drag. Not moving can cause pressure to be transferred

to the center electrode with resultant cracking.
 
The above is a good example where car stuff doesn’t exactly translate to plane stuff. Always learning from you kooky A&P types. Thanks for coming here and sharing your knowledge for free.
 
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