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Rapid plug failure in Chummy
#12
Hi

All those plugs look very oily, so maybe it's a bit unfair to blame the plugs themselves. Few of our engines get hot enough for long enough to get the insulators up to the self-cleaning temperature. I too have had good results with NGK B5HS, the 5 rather than 6 heat rating helps in this respect.

I have recovered fouled plugs in the past by heating the tips up with a gas flame till they are dull red and allowing the oil/carbon mix to burn off. A garage would never do this as it's not economic at £100 an hour, but if your time is free there's nothing to lose. Beware of wire brushing or scraping as this can just embed particles of metal into the insulator ceramic which is the last thing you want.

I suggest you double check the rest of the ignition system, as a weakened spark is less likely to fire a marginally fouled plug.

If you test plug insulation resistance with a multimeter, any reading of less than 1 Megohm should be treated with suspicion. Anything less than about 200 kilohms and it probably won't fire. However, this is not definitive, as testing at a few volts in this way won't show up a plug which only fails at high voltage. By contrast, I have checked good plugs at 1000 volts DC with an insulation tester and the resistance was above 5000 Megohms.
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Messages In This Thread
Rapid plug failure in Chummy - by PeterN - 28-07-2024, 01:18 PM
RE: Rapid plug failure in Chummy - by PeterN - 28-07-2024, 02:03 PM
RE: Rapid plug failure in Chummy - by Jeff Taylor - 28-07-2024, 02:57 PM
RE: Rapid plug failure in Chummy - by PeterN - 28-07-2024, 03:53 PM
RE: Rapid plug failure in Chummy - by PeterN - 28-07-2024, 05:36 PM
RE: Rapid plug failure in Chummy - by PeterN - 28-07-2024, 06:14 PM
RE: Rapid plug failure in Chummy - by John Cornforth - 28-07-2024, 09:21 PM
RE: Rapid plug failure in Chummy - by Nick Turley - 30-07-2024, 12:03 AM
RE: Rapid plug failure in Chummy - by Charles P - 30-07-2024, 07:21 AM
RE: Rapid plug failure in Chummy - by Charles P - 30-07-2024, 11:32 PM

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