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Old 11-09-01, 11:58 AM   #1
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Recycling spark plugs...

Alrighty, I change my spark plugs every 10k miles. I'm sure the spark plug could easily last longer than that, but a bit of carbon and *stuff* builds up on them causing them to be less efficient.

Would it be a safe bet that I could clean the plug with a wire brush and use them again? I cleaned one off and it looked shiney and new again, but I'm not sure it if would work well for another 10k or not.

I'm not exactly sure what part of a spark plug wears out when it dies, but I'm certain that a good quality spark plug will go good for at least 40k.
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Old 11-09-01, 12:06 PM   #2
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the plugs dont last so long in our cars b/c they fire so many more times than boingers(6x more i guess if its 3x per revolution in teh rotary and every other rev in a boinger)

but it definately dosnt hurt to take em out and clean em once in a while and put em back in. get a little more life out of em. i'd still change em at least every 15k though just cause
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Old 11-09-01, 12:09 PM   #3
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Quote:
Originally posted by niner
the plugs dont last so long in our cars b/c they fire so many more times than boingers(6x more i guess if its 3x per revolution in teh rotary and every other rev in a boinger)

but it definately dosnt hurt to take em out and clean em once in a while and put em back in. get a little more life out of em. i'd still change em at least every 15k though just cause
I'm just wondering if I can yank 'em out at 10k, clean 'em, and use them for another 10k.

I probably won't do this, I just want to know if it would be safe or not.
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Old 11-09-01, 12:21 PM   #4
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if you want. wouldnt hurt nothin
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Old 11-09-01, 12:46 PM   #5
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Change them out if the metal is getting worn. I wirebrush mine every few months so the carbon doesn't build up too much. This method seems to work for me.

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Old 11-09-01, 02:06 PM   #6
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The plugs start dieing big time after 30k miles, and there is an appreciable change in performance at 15k miles.

Sparks work best firing between two sharp edges, as the plugs wear, each fire of the plug slowly removes minute amounts of metal from the spark edge. After a while the edge becomes rounded, leading to a traveling spark. A traveling spark requires considerably more energy to light than a clean spark from edge to edge. So now your spark is just trying to use all the power the coil can give it, just to bridge the gap, rather than having an intense spark to ignite the mixture.

So you could file the edges back down flat and sharp, re-gap the plug, but the filing will slightly change the temp range of the plug, as the center electrode will be slightly lowered into the insulator.

Actually in the old days of distributor caps an old racers trick was to grind the rotor inside down to a razorblade edge, to make perfect edge for the spark to jump to.

Now some people claim that platinum plugs work as well, but the biggest drawback to them is that the insulator runs all around the tip, so as the plug wears, the gap gets bigger and lower into the insulator, but you can't adjust it. So the idea of they last longer is not very accurate, sure the perceived adjustable gap doesn't get any bigger, but because the electrode is burning itself up in the insulator the gap is growing bigger and bigger. So unless you have a Jacobs box on there the spark gets weaker and weaker.

So donít re-use any plug with over 15k miles on it if you want max performance. If you donít care about max performance, the by all means use the plugs up to 30k miles.

BTW: make sure you replace the stock plug wires at least every 60k miles as well.
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Old 11-09-01, 02:34 PM   #7
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Quote:
Originally posted by Icemark
So donít re-use any plug with over 15k miles on it if you want max performance. If you donít care about max performance, the by all means use the plugs up to 30k miles.

BTW: make sure you replace the stock plug wires at least every 60k miles as well.
Thanks for the tips.

I usually install brand new spark plugs every 10k miles.

I have new wires on the way, the ones I have are shot. The trailing plug on the front rotor only fires every once in a while. Due to not firing some of the time that plug has become very gummed up with carbon deposits then it stops firing completely. When this happens my ECU flashes me an O2 sensor error.

My MSD 8.5 wires are supposed to be in today, I really hope they are.
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Old 11-09-01, 03:21 PM   #8
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Quote:
Originally posted by niner
the plugs dont last so long in our cars b/c they fire so many more times than boingers(6x more i guess if its 3x per revolution in teh rotary and every other rev in a boinger)

but it definately dosnt hurt to take em out and clean em once in a while and put em back in. get a little more life out of em. i'd still change em at least every 15k though just cause
Actually, it's just once per plug per revolution of the crankshaft.. The rotors make 1 full turn for every 3 crankshaft turns..

But yeah, it does seem like our cars eat them up.. and they're expensive!

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Old 11-09-01, 05:03 PM   #9
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Hey a couple of things I forgot to mention in my last post....

always use a dab of anti-seize compound on the plug threads

This goes for most aluminum headed creatures motors, but doubly so for a rotary.

And replace the crush washers every other time, if you are pulling the plugs regularly to check them. Its pretty common to have a plug back itself out if the crush washer is worn.
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Old 11-09-01, 06:41 PM   #10
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Icemark, the nuggets of rotary wisdom you come up with......

1st beer at the next Sevenstock is on me..........

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Old 11-09-01, 07:00 PM   #11
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Given that I change my plugs every 15k miles.

Does it matter whether or not I use the platinum plugs?

Given that the BUR9EQP's are $12-15
and that the BUR9EQ's are $4-5

What would be the best performance? You can buy 3x as many non-platium plugs for the same price. Is it better to use the 9EQ's and replace them more often rather than getting the 9EQP's?

Also, i've been told that I might want to run 9's on both the trailing/leading plugs, is this a good idea?

I'm running 12-14lbs of boost on a street ported FD with a high-flo exhaust/intake, 1 extra 550cc injector and a greddy fuel computer.

Details...http://www.hybit.com/~jriskin/rx7/fd/

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Old 11-09-01, 07:00 PM
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