Roughness On Run Up

My Cont TSIO 520 was a little rough on start up from cold in about 45* weather, but seemed to smooth out as it warmed up. After about 10 minutes the mag check was good on the right, but decidedily rough and missing on the left magneto. I didn't have any tools with me nor a spare plug as I have had such good service with this plane that I don't carry either. I used to carry both with a another plane. I have not had any times when this engine fouled a plug which then cleared on run up, so I didn't think that was going to be the cure. I am at Front Range airport, and was glad to find mechanics there on Sunday morning. Its not easy to trace the plug wires from one mag to the plugs since they are bundled together, but the mech pulled all the top ones which have easy access. and of course no problem found. Getting to the bottom ones is harder but sure enough the front cylinder, think it is 5 or 6 on the right side, had a bad plug, half the insulator was broken off of the center electrode, and the shop didn't have a new replacement plug since these are 32 S,fine wire ones. Any we hope to find one locally in the morning. Glad I didn't try to fly, and just hope it would be better in the air. It would have probably run ok on the good plug ,but I would have been given up my dual ignition backup. There is a lot of pr for Tempest plugs these days, but I have always used Champions and seemed to work well, this only the 2nd cracked plug Ive had in over 10 years or about 1000 hours. New ones are about $85 a piece, so its good that they last a long time. The outside of mine look old but the electrodes still look good, even on the broken one. Not sure why it broke, bad plug or backfire starting or just age and chance, but it was no doubt about rough. The FBO has a big screen tv where I got to watch the Longhorns smite the purple toads just as it used to be and should be once again.

My big concern would be, where did the porcelain go and what damage did it do on the way out. I've seen them get stuck between valve faces and seats, causing damage that would later lead to a valve failure, as well as a miss . I would scope it will and do a leak down test. As for the failure, 90% of the time its knock causing the porcelain to crack in my experience.

What did the other plug in that cylinder look like?

Thanks, all the other plugs looked good , normal. We'll see on run up if there are any problems but neither I nor the a& p are expecting any, I think the small piece of insulator just went out the exhaust.
If the piece had dmaged the valve it would not run well on the other mag which it does like normal.

I think Im ready to go now, 11am the next day. 2 hours labor at $75 per seems reasonable , but the new plug was $140 and of course that was full retail but even at Aircraft Spruce they are listed at $107 plus tax and shipping. I think the electrodes are made from angel hair, though they say "iridium" which is like platinum I think. And of course with the plane ready to fly now the weather is worse and even have an icing report at 16,000 ft right where I need to fly.

Ive had 2 flights now and the engine runs smooth and normal.IT'S hard to imagine that taking one spark plug away which takes one cylinder away when running on one mag would make it that rough. One cylinder, of a 6 cylinder engine is 16%, but it feels more like half, it feels and sounds rough. Great to have nice mechs available on a Sunday. What a major step forward in safety and convenience it was back about 1920 or 1930 when engines routinely started using 2 parallel ignition systems., so youve always got that built in back up.

I would want to know what caused the porcelain to break? In all my years I have never had this happen unless there was another underlying cause. Be it the plug was dropped, preignition..ect.

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Originally Posted by 1600vw

I would want to know what caused the porcelain to break? In all my years I have never had this happen unless there was another underlying cause. Be it the plug was dropped, preignition..ect.

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Dropped on the floor at the last annual.

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Originally Posted by FlyingRon

Dropped on the floor at the last annual.

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Is this what happened or a guess? If any mechanic did this and did not throw out said plug. IMHO said mechanic should be fired from said job. On an auto, if I drop a plug it don't get used. I have thrown many a new plug out because of this. It happens. But a good wrench would never use a dropped plug.

I have seen broken porcelain on plugs from over torquing to being dropped on floor and reinstalled. As for waiting for another fine wire plug to show up, a "massive electrode" plug would have gotten you home with no problems.

Bill Landry

Yes I could had used a standard massive electrode type of spark plug, that is one that looks like in a car engine. The repair shop had a massive one in stock. and it is about $50 as opposed to $140 for the fine wire one. But I prefer the fine wire type and that is what is recommended for my plane and engine. My plane is turbocharged, I live at 8000 ft and I often fly above 16,000 ft. The fine wires work better at high altitude and they last a lot longer. Even my old ones look old on the outside but the electrodes look almost new after hundreds of hours. So you get you moneys worth from them. If I had bought the massive one, then the next day Id have gotten the fine wire one so really paid twice.
I don't know if the fine wires are do expensive because of precision needed or the iridium metal.
There's no evidence of anyone dropping my plug, it has been a year and 100 hours since the annual and was running fine. I didn't drop them or ovetorque them. As for as dropping, plugs are shipped in boxes and fed ex or ups or whoever drops the boxes. I have some doubts it the plugs are really that fragile. I have put a dropped one on the tester and it fired normal. I may send the plug to Champion to see what they say.

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Originally Posted by Bill Greenwood

Yes I could had used a standard massive electrode type of spark plug, that is one that looks like in a car engine. The repair shop had a massive one in stock. and it is about $50 as opposed to $140 for the fine wire one. But I prefer the fine wire type and that is what is recommended for my plane and engine. My plane is turbocharged, I live at 8000 ft and I often fly above 16,000 ft. The fine wires work better at high altitude and they last a lot longer. Even my old ones look old on the outside but the electrodes look almost new after hundreds of hours. So you get you moneys worth from them. If I had bought the massive one, then the next day Id have gotten the fine wire one so really paid twice.
I don't know if the fine wires are do expensive because of precision needed or the iridium metal.
There's no evidence of anyone dropping my plug, it has been a year and 100 hours since the annual and was running fine. I didn't drop them or ovetorque them. As for as dropping, plugs are shipped in boxes and fed ex or ups or whoever drops the boxes. I have some doubts it the plugs are really that fragile. I have put a dropped one on the tester and it fired normal. I may send the plug to Champion to see what they say.

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Have you ever wondered why plugs come shipped like the do? In the protective container they come in? Even a quality auto plug will be protected in the box from such handling practices. Porcelain breaks very easy. The problem, when you crack the porcelain most time the porcelain will not come apart. It will hold together. Seeing how this porcelain is down deep in the plug you can not see this broken porcelain. Then under combustion pressure the plugs porcelain comes apart. The combustion camber is a very violent environment.

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Originally Posted by 1600vw

I would want to know what caused the porcelain to break? In all my years I have never had this happen unless there was another underlying cause. Be it the plug was dropped, preignition..ect.

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Most common cause of porcelain fracture in service is detonation.

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Originally Posted by 1600vw

Have you ever wondered why plugs come shipped like the do? In the protective container they come in? Even a quality auto plug will be protected in the box from such handling practices. Porcelain breaks very easy. The problem, when you crack the porcelain most time the porcelain will not come apart. It will hold together. Seeing how this porcelain is down deep in the plug you can not see this broken porcelain. Then under combustion pressure the plugs porcelain comes apart. The combustion camber is a very violent environment.

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Yes, the drop was just a guess as to "how could this have happened."

1600VW is right about this. It's very hard to test for failure of these high tension insulators. And just because it passes after it was dropped doesn't mean it doesn't still have a latent defect that fails a time later.

$140 for a spark plug!
I am glad I bought Pmags and use $5 BR8's.
Try gaping your massive plugs to .40 and get that old 1940 tractor mag to fire them.

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Originally Posted by Bill Greenwood

Yes I could had used a standard massive electrode type of spark plug, that is one that looks like in a car engine. The repair shop had a massive one in stock. and it is about $50 as opposed to $140 for the fine wire one. But I prefer the fine wire type and that is what is recommended for my plane and engine. My plane is turbocharged, I live at 8000 ft and I often fly above 16,000 ft. The fine wires work better at high altitude and they last a lot longer. Even my old ones look old on the outside but the electrodes look almost new after hundreds of hours. So you get you moneys worth from them. If I had bought the massive one, then the next day Id have gotten the fine wire one so really paid twice.
I don't know if the fine wires are do expensive because of precision needed or the iridium metal.
There's no evidence of anyone dropping my plug, it has been a year and 100 hours since the annual and was running fine. I didn't drop them or ovetorque them. As for as dropping, plugs are shipped in boxes and fed ex or ups or whoever drops the boxes. I have some doubts it the plugs are really that fragile. I have put a dropped one on the tester and it fired normal. I may send the plug to Champion to see what they say.

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