Spark plug lead fouling issue

[DaV8or]

This is sort of a follow on thread after my Slick Start thread. It turns out the reason my engine wouldn't start the other day was because all four of the lower plugs had significant lead fouling. I cleaned it all out, checked the gaps and the resistance, put them back in and she fired right up even with a weakened battery. The lead fouling was bad enough in just under 30 hours since they were cleaned at annual to prevent the motor from starting.

 

Only the lower plugs were effected. The upper plugs looked fine. In addition there has always been lead deposits caked on the tops of my pistons. I lean all the time. Aggressively on the ground, usually so much that I have to richen just a bit to be able to do the run up, during climb I use the target EGT method and in cruise I run LOP. I remain leaned during descent and only in the traffic pattern during the GUMPS check do I go full rich for a go around. Once on the ground, I lean again.

 

I'm not sure why I seemed to be more plagued by lead than some of you, but one theory I have is that my cylinders seem to run quite cold. Running LOP only makes that worse and I have read that if CHTs don't get hot enough, not all the lead will be scavenged. Ideas that I've had to potentially improve this situation-

• Use TCP in the fuel. I don't really like the added expense and the stuff is a hassle and pretty nasty.
• Go to a hotter heat range plug. Currently running 38s and Lycoming does allow the use of 37s.
• Go to fine wire plugs. I really don't want to spend $600-700 if it's not going to make much difference.
• Maybe just go fine wire on the lower plugs since that's where the problem is. I'm not sure if this is allowable, or good to mix plug types. I guess it messes up the rotation.

I really don't have any other ideas other than throwing caution and the regs to the wind and burning MOGAS. Are there any other solutions? Has anyone else had this issue? Fouled plugs in just 30 hours is unacceptable IMO. The only saving grace is the FAA allows me to clean the plugs myself.

[Yetti]

One thing I was taught whenever you are sitting keep the RPMs between 1100 and 1200

[PTK]

Based on your description I would only comment on a couple things.

One thing I'd tell you is don't go full rich in the pattern. That's the worst phase to go full rich. Only go full rich the times you go around. How many times do you actually go around and not land? I bet you land a lot more!

Manifold pressure is low and your CHT's are cooling down even more. Flooding it with fuel here serves no good purpose. It only sets the stage for plugs to foul up.

The other would be to lean very aggressively on the ground. On the run up only enrichen gradually to sustain it up to your run up RPM, (mine is 2000 RPM) and no more.

How cold do your CHT's run?

[ryoder]

I don't go full rich when I'm in the pattern. I go partial rich. Carb heat plus full rich is a recipe for fouling and I learned this doing long finals on the localizer. I don't go around very often so I fly the egt all the way to short final and then I go almost full rich. I also run kind of hot and have fine wire plugs.

[stevesm20b]

I went to the 37BY plugs and it cured fouling problems.

[Andy95W]

I have fine wires on the bottoms only and couldn't be happier. I now rotate my plugs 1-2-3-4 Top and 1-2-3-4 Bottom. Works great.

And I never have to clean a bottom plug between annuals.

I also lean in the pattern, aggressively, and go to full rich and carb heat off as I cross the threshhold.

[DaV8or]

How cold do your CHT's run?

 

It changes winter to summer, but in winter the front two cylinders never go over 300. they rear hover around 320. Summer seems to have just started around here and this weekend had highs in the low eighties. Today I got my first automated density altitude warning of the year. IIRC, today number one was around 305, number two at about 290, number three at 340 and number 4 at 320. Only on climb out, during the middle of summer do my rear cylinders potentially exceed 380 degrees. The cowl flaps on my plane are very ineffective at regulating heat. I guess they fixed that with the J. Open/closed, makes little difference, but I do go through the motions. They kind of remind me of the fake retractable antennas they used to put on cell phones back in the '90s to make you feel like you could actually do something to improve the reception.

[DaV8or]

I went to the 37BY plugs and it cured fouling problems.

 

Good to know! Thank you!

[DaV8or]

I have fine wires on the bottoms only and couldn't be happier. I now rotate my plugs 1-2-3-4 Top and 1-2-3-4 Bottom. Works great.

And I never have to clean a bottom plug between annuals.

I also lean in the pattern, aggressively, and go to full rich and carb heat off as I cross the threshhold.

 

Good to know! Thank you! The reason I don't lean in the pattern is I know me. I know it is unlikely in the event of a real go around that I will remember to go full rich. However, at the first GUMPS check, rarely is anything really going wrong and I can remember then to go full rich. My experience has shown that in the event of a real go around, the only thing I can reliably remember is throttle, followed by eventual flaps. I fly at an often busy non towered field. There are many times distractions in the pattern when checklists go out the window and looking, followed by action, take over.

[Super Dave]

Maybe lean even more on the ground? You said you need to enrichen for runup, but I try to lean so much that the engine stumbles at anything over 1200RPM.

[ryoder]

My instructor flew the mooney for a trip last weekend and I told him to wait until short final to lean and to lean till it quits on the ground and fly rich of peak during cruise climb. I know he did because when I got it back it wasn't fouled.

[RobertGary1]

On the ground if adding throttle causes the RPM's to rise you are too rich. Lean it until its almost going to cut out. There is absolutely no risk of over leaning damage on the ground because you are not producing enough power to cause issues.

 

I don't go full rich on final either. So go around would would be a two step process. Its a technique I learned while at the Cessna Factory doing my Cessna Factory Authorized Instructor course. In the T206 the engine will quit at low power settings at full rich. Not a problem in the Mooney but similar technique is beneficial. 

 

 

-Robert

[PMcClure]

I struggled with lead fouling until I switched to fine wire plugs on bottom. Different engine than yours but not once since changing (over 1 year now) have the plugs fouled. 

[garytex]

The magic number for EGT lead scavenging is 1200 df. Below 1200 the scavenger in hundred low lead does not work. So that's you target for ground ops, try to keep EGT's above 1200.

Something is up that your cowl flaps don't make any difference. I have the same cowl that you do, Southwest Texas aviation and my flaps are good for about 10°. It does however take a few minutes for the effect to be seen. And I wrapped the bottoms of my cylinder bases, yours may be unwrapped.

Gary

[RobertGary1]

The magic number for EGT lead scavenging is 1200 df. Below 1200 the scavenger in hundred low lead does not work. So that's you target for ground ops, try to keep EGT's above 1200.

Something is up that your cowl flaps don't make any difference. I have the same cowl that you do, Southwest Texas aviation and my flaps are good for about 10°. It does however take a few minutes for the effect to be seen. And I wrapped the bottoms of my cylinder bases, yours may be unwrapped.

Gary

Its really hard to give absolute EGT numbers. The EGT readings are heavily influenced by the location of the probe. That's why its so important to very precisely measure the distance down the stack you drill the probe holes so each cylinder reads relative to the others.

 

-Robert

[N601RX]

When I 1st got my plane it had massives and if I forgot to lean I would get a rough run up. Sometimes a high power lean runup would clear them, other times it required removing the plug.  After replacing them with fine wire it has not happened again in 150hrs.  At annual there wasn't anything to clean, they are already clean. I have 8 extra massive plugs and a spark plug cleaner if anyone is interested in a deal on them.

[DaV8or]

The magic number for EGT lead scavenging is 1200 df. Below 1200 the scavenger in hundred low lead does not work. So that's you target for ground ops, try to keep EGT's above 1200.

Something is up that your cowl flaps don't make any difference. I have the same cowl that you do, Southwest Texas aviation and my flaps are good for about 10°. It does however take a few minutes for the effect to be seen. And I wrapped the bottoms of my cylinder bases, yours may be unwrapped.

Gary

 

They are unwrapped I believe. I'm not really sure what "wrapping" is like, but mine have nothing on the bottom. There is a "plug" as it where, between the cylinders on the bottom though. I think my plane would idle at 1000 rpm all day and not reach 1200 on the egt no matter what I did with the red knob. Next flight I'll see.

[DaV8or]

I'm gathering that I need to invest in some fine wires and maybe lean some more, but I'm already pretty lean. It makes me wonder, what did people do in the '60s and '70s? The POH sure doesn't give any mention of leaning until the brink of dying and going full rich in the pattern was SOP. I don't think fine wire plugs existed back then either. Did they really have to pull the plugs and clean them every 25 hours or so?? I wonder fine wire vs. the 37BY plug. No way to know for sure I guess. How do you gap the fine wires? I have the tools for the massives, but not sure about fine wire. They look like if you touched them they would break easy.

 

Anyhow, thanks for the replies so far!!!

[Andy95W]

I think back in the 60's and 70's they cleaned sparkplugs more often.

I recommend Tempest fine wires. You don't adjust the gaps on them, only check them. If they are out (rare) Tempest asks that you send them back so that they can do them. That way they can make sure they get done without breaking them.

[PMcClure]

I did have an F and flew it several 100 hours. If I didn't lean 2 fingers after start-up, I would be fouled by the run-up. I would also say that the 69F POH left a lot to be desired!

[helitim]

Just got back from the Aviall conference today. The Champion tech rep did a presentation and stated emphatically that he recommends 37BY's to anyone that needs a hotter spark and does not want to run fine wires.

[RobertGary1]

If you lean very aggressively on the ground to fine wires are not necessary. The fine wires are just more forgiving. I ran them for a couple of years when I was pumping oil but otherwise probably have 15 years of running massives without issue.

-Robert

[Hondo]

CHTs below  300°F cause lead fouling. 

To prevent lead fouling, avgas contains a "lead scavenging agent" called ethylene dibromide, which dissolves excess lead and passes it out the exhaust pipe. However, ethylene dibromide doesn't work effectively unless combustion temperatures are fairly high. That's why lead fouling problems tend to emerge when CHTs are below about 300°F.

If possible, the 325 to 375 range works well. That's hot enough for effective lead scavenging and cool enough to keep the cylinder heads and valve guides happy.

Advice  from Shell.

http://www.shell.com/global/products-services/solutions-for-businesses/aviation/aeroshell/knowledge-centre/technical-talk/techart18-30071600.html

[Yooper Rocketman]

When I picked up the Bonanza at Tornado Alley, after the new engine install and turbo upgrade was completed for Northwoods Airlifeline (a mercy flight organization I fly for), I had to fly it and be signed off by their test pilot.  He was very specific about the leaning process, and taught exclusively LOP operations.  We leaned until the engine almost died immediately after start up, and only went full rich as we rolled on to the active.  Once leaned in cruise, he said don't touch the mixture again unless you are going missed on a landing.  I had no problem with the process of mixture-throttle on missed, as I had been doing this all along on my Rocket anyway.

 

I've run fine wire plugs a ton of hours on both my Mooneys and have had lead in the bottom plugs, needing to clean and rotate them every 100 hours, so can't say that problem will go away just by buying fine wire.

[carusoam]

Hondo,

Nice reference!

My C was good at collecting Pb balls...

Leaning on the ground minimized this challenge, but didn't eliminate them.

The Shell paper adds another procedure of interest, 1800 rpm for 15 seconds before shutdown....

Anyone perform this step in their shutdown procedure?

Best regards,

-a-