clogged up spark plug = mag drop

Z

zubbo

New member
Hi Guys,

Need advise again on my 7gcaa citabria 1973: Had a mag drop last week and found the bottom spark plugs to be clogged up. The local Amo told me the rings might have to be replaced because oil could be leaking around the pistons. The engine was overhauled with new rings 400 hours ago and the last blow buys (10 hours ago) was between 68 and 75 out of 80. The new airfield I am at have 25 min taxi before take off and some tell me it could be too low revs on taxi. I get the feeling Amo`s want to make money immediately even though problems are standard? Anyone else had the same kind of problem? -any advise what to do?

zubbo (ZS-MYH)
 
I am not an A&P or an IA but I have been flying for many years and have had a many aircraft. Almost eveyone of them have had a fowled plug at one time or another, usually a lower plug. My first reaction would not be to remove and rebuild a cylinder. I might pull the plug and possibly swap with a better, newer upper plug and see if the condition reoccures. The 65/80 seems low while the other cylinders are 75/80. This would require some attention. Many situations could cause this. It is possible the gaps in the rings on that cylinder have lined up temporarily allowing oil to pass. Not sure I have ever seen this condition but seems possible. I do not know if this is a good or bad practice but I know one person that soaked a cylinder with low compression in marve mystery oil (simply filled the cylinder) and allowed it to sit a week or two. He says it freed up the rings and worked. My experience with a fowled pug was never caused by low compression, usually bad plug or wire. I have even run into a situation where the spring on the end of the wire was corroded or broken and not making good contact with the plug. Hope this gives you some hope and causes you to think twice about letting somebody simply jump into changing a cylinder.

Ken
 
25 min taxi before take off
Click to expand...

I think this might have something to do with your problem. Of course, aircraft engines don't necessarily do well unless they're flown.

One thing you might try is ground leaning. If I had to taxi that length of time, I would pull the mixture out until just before the engine cut off. It would be to the point that if you increased the throttle the engine would actually sputter and quit. That, of course, would prevent you from forgetting to push the mixture in for take-off. During taxi, with the mixture out that far, you're running the engine pretty lean. At low rpm's there's literally no chance that you'll cause damage to your engine, if you're concerned about that. If you needed to increase rpm slightly, you could push the mixture in a little and that would add some rpm.

With the mixture fully in during taxi, the engine is really running rich. That is, there is excess fuel in the combustable mixture. This excess fuel leads to fouled plugs if your taxi time is extended such as yours. Of course, the excess fuel for takeoff is a good thing as it cools the cylinders.

I've been doing this with my AEIO-320 for about a year with good results. Although, my taxi time is considerably less than yours.

Jon
 
Hi, first is the plug lead fouling or oil fouling ? If its from oil then you may have a cylinder problem, could be the rings or it could be a worn valve guide not to likely on a 400 hr engine but could be. If its not but lead fouling then as posted leaning while taxing will help, Marvel Mystery oil in the gas will help and and a big help is when you get back to the hangar cool down the engine for 2 min. at 1100 / 1200 RPMs this will scavenge the lead out of the cylinders and use the idle out off to stop the engine, then every 100 hrs pull the plugs clean them and rotate the top plugs to the bottom etc. Or it could be a bad plug as posted easy to pull the plug and test it.
 
A young friend and I bought a 7-ECA together for him to learn to fly in. Lots of full-stop landings, ground time, power reductions in the air, no leaning, etc. followed and at the first annual (about 50 hours since the plugs were supposedly cleaned by the previous owner and about 100 hours since the plugs were new) the bottom plugs were so badly lead fouled the mechanic first recommended throwing them away. After much work we did get them clean.

He gave us a publication that is a compilation of key maintenance and performance articles taken from the former Lycoming "FLYER" Newsletter. One article specifically addresses leading. In general it confirms the advice given above, but has more detail. In both air operation and ground operation proper leaning and avoiding rapid engine cooling or power changes are emphasied. Curiously, for shut-down the same 1000 to 1200 RPM temperature stablization is recommended, but it continous after the temperatures have stablized "the engine speed should be increased to approximately 1800 RPM for 15 to 20 seconds, then reduced to 1000 to 1200 RPM and shut down immediately using the mixture control."

We have been agressively leaning on the ground, leaning per the book in the air, and doing the shutdown procedure. We still get some lead fouling, but the problem is MUCH better. Ron did get his ticket (btw he has zero tri-gear time). but may still be a bit timid with the red nob.

I have no idea how you might get this publication. If you want it, I suggest you try Lycoming themselves. Mine is copyright 2006 by Lycoming and has a price of $4.99 on it. It has over 100 pages and covers lots of subjects.

Hope this helps.
 
An interesting side light to leaning! I just bought a 73 Decathlon, the oil looked like it had just been changed. I was told, to my surprise, that the oil had not been changed in the last 25 hours. I was also told that the oil was clean because th operator always leaned, on the ground and in the air. There is a JP fuel flow meter in the aircraft the method of leaning was, lean to sputter and then add .5 gal per hour flow. I disregarded the information but, I can tell you I have put only about 2 hours on the aircraft since I bought it, have not leaned since I do acro, and the oil is now showing signs of use through oil color. I wonder if the original owner was on to something?

Ken
 
kpin, our oil stays clean looking also. We have a good tight engine (400 hrs on Lycoming 0 time) and do little acro, but do consider ours hard oil service since we are on a grass strip, have only a T hanger, see lots of short flights and lots of landing practice, and experience lots of dust in the air. Everything outside gets quite dirty quickly, but the oil is amazingly clean looking when we change it. I can't back it up with fact, but I feel like the leaning contributes to the clean looking oil.
 
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