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T-Series Odd spark plug encounter!

PAUL161

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A while back I commented on my TFs engine developed a stumble when running at a high idle and higher under a no-load condition, needless to say, I tried everything to find the cause, new points condenser, rotor, distributor cap, even new plug wires, and proper ends. I was pretty sure it was an ignition problem. The plugs only had 150 miles on them so I left them alone. Checked entire fuel and electrical system, no problems. Decided to pull the plugs even though I knew nothing was wrong with them, but when I pulled the last plug, no.4, I found this, the center ceramic had broken free up inside the plug and slid down covering the end and intermittently blocking the spark. The pics are the same plug showing the ceramic in both positions. Never saw this happen in a normal running engine, even when we were racing years ago I never encountered this situation.
smoking smiley
PJ

Bad TF plug 2.jpg
Bad TF plug.jpg
 
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PAUL161

PAUL161

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I opened up the plug and found where the ceramic broke. It appears to have broken on its own without anything touching it, odd, very odd.
Broken ceramic.jpg
 

bobhustead

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Maybe a misstep in gapping the plugs? E.G., those slotted blades on some feeler gauges for bending the ground electrode can get into funny positions. Glad you found it.
Bob
 

LarryK

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I had a plug seperate the porclein on the top and would rattle each compression stroke. You could shake the plug and it would rattle. Happened on my V-12 Jag S on the way home from work, thought I had dropped a valve. Did not notice the miss on the 12 but the heart settled down when I found the plug.
 
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PAUL161

PAUL161

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Fired it up this morning with new plugs and she runs like a champ all the way up the scale. Idles as smooth as silk! Thanks for the comments and possible causes, much appreciated! (y) PJ
 

Gliderman8

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Glad you found it Paul. Things like that can drive you crazy trying to find the cause.
A couple of years ago I had a head scratcher on my '63 Lambretta. When braking the engine would die. I could start it immediately and continue driving. Like you I began replacing components. It turned out that the spark plug wire was too short. When braking, the rear of the scooter would slightly raise "stretching" the spark plug wire and momentarily pulling it out of the coil. After I installed longer wire the problem went away.
 

LarryK

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Seems it's always the simplest of things.
 

DrEntropy

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One of the best caveats ever heard: "Check the Stupid Stuff first!"

We've had many a plug defective "outta th box" in the shop. Always look to the last thing you touched first, before "inventing" new problems. ;)
 

blueosprey90

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I too have been chasing a high speed misfire above 4,000 rpm. Last year I had a similar problem above 5,000 rpm. Whether the spark plugs are the smoking gun, remains to be seen.

I took my plugs in to do a resistance test on the multi-meter. Not knowing exactly what I was doing, but two plugs seemed to show no resistance. I checked a few others with inconclusive results, so I came in to watch a You-Tube video to determine what I should be doing. Once I understood the process, I went back to test my plugs again.

I mostly run B8ES NGK plugs, although I did try some B9ES plugs this year as well as a set of BP7ES. For most of the year, my timing was retarded, and I was running hot. I think I have the timing issue sorted.

I tested a total of 23 used plugs. Twelve showed resistance. Eleven showed no resistance. All four of the BP7ES plugs showed no resistance - one seemed to show some burn at the porcelain insulator. Three of the four B9ES plugs showed no resistance.

I'm guessing that there is an internal break in the electrode and that the spark is able to jump it more or less successfully at low rpm, but not so well at high rpm. At 4,000 rpm, we are talking about 66 revolutions and spark firings per second. At 6,000 rpm, that increases to 100 revolutions and spark firings per second!

The used plugs that showed resistance and were deemed "good" showed resistance from about 3 ohms to 35 ohms.

I bought 8 new B8ES NGK plugs. Seven showed resistance of 0.8 ohms. One showed resistance of 135 ohms.

These are all low resistance plugs. I've been running with a .030 " gap that I maybe need to reduce. And I better start using a torque wrench when installing to insure proper het transfer to the block.

Will be running the car this weekend, so wish me luck.
 

DrEntropy

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