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BigTex

Fine Wire Spark Plug Gapping

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I just spring for a set of fine wire spark plugs and just realized that I forgot to pick up a gapping tool. Do these plugs come with the gap already set ready or do I need to chance down a tool to test them before installation?

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Our Tempest plug gap was set to .018 out of the box but we reset it to .016.  You can use a feeler gauge and a pair of duckbills to set the gap, it is easy to fit the feeler in there.  I have heard that you can only reset the gap 2-3 times before breaking the fine wire electrode, so get it right the first time. You wont have to reset the gap again for a thousand hours.  They just don't wear like the massive electrode plugs do.  Don't use an abrasive blaster to clean them, either. Just pick the lead out with a piece of safety wire. The abrasive strips the iridium coating from the electrode, causing the plug gap to wear out fast.

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Thanks Byron... The specs show .017 - .021. Was there a reason why you went outside of the specs?

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The M20J SMM section 71-00-00 lists fine wire spark plug gap as .015 to .018.

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I recently replaced the Champion fine wires in my Mooney with Tempest. Champion's internal resistor design is not sealed and resistance had increased far beyond spec. Thought I'd try to fix the Champions by replacing the resistors with some salvaged from a set of massive plugs (Champion doesn't sell the resistors seperately) . . . that would have worked, but the internal contacts in the Champion where corroded beyond repair - - I even made a reamer to try and clean the internal contact - - but the metal was all eaten away and all I got was brown powder that looked like rust.

 

This flawed "non-sealed" resistor design isn't so much an issue with Champ massive plugs, as the plugs are replaced more often, but with fine wire plugs, whose electrodes will often last to engine TBO and beyond, internal corrosion, arcing, and high resistance takes out the plug long before their time.

 

For fine wire plugs, Tempests are the better deal.

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Yeah... I went with Tempest as well. It will be interesting to see if they improve my EGT spread. Having a carburetor, I don't have the luxury of tuning injectors.

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They will break very easily so be careful. I found out the hard way only trying to tweek one a little. After that I got the Champion tool, it works fine on the Tempest plugs. Its a little expensive, but cheaper than a new plug.

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I lucked out as none needed the gaps adjusted. So what makes that tool worth the $50 they're asking?

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I didn't think it was worth $50 either, But thought it was a pretty good deal when I felt the fine wire snap off. However it does work well. It has a small square groove milled in the end of it that fits over the fine wire. It gives you a easy way to grab the wire and tweek it a little. If they are bent very much they will snap off.

I'll post a pic of it next time I'm at the hanger

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I've been adjusting fine wire plugs with a pair of needle nose pliers for 30 years and I've never broken an electrode.

 

Has anyone actually broken one, or is this an old wives tail?

 

Maybe I'm just lucky...

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Yes, I was using needle nose trying to close it up about .005. It was at about .023, all the others were at .018. It snapped off. I've done others before and never had a problem. It was a new plug and still sealed up. It was the only one of the group that wasn't correct from the factory. It didn't really move any, just snapped.

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Also, I've always sand blasted my fine wire plugs and they seem to last about 1000 hours.

 

They probably get blasted 10 to 15 times in their life. I always use glass beads in my cleaner which are pretty gentle, but I think this sand blasting thing is an old wives tail too..

 

I'm going to stick to clean spark plugs...

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Yes, I was using needle nose trying to close it up about .005. It was at about .023, all the others were at .018. It snapped off. I've done others before and never had a problem. It was a new plug and still sealed up. It was the only one of the group that wasn't correct from the factory. It didn't really move any, just snapped.

 

I've never tried adjusting one right out of the box, they are always right on. Maybe running them anneals them and makes them less brittle.

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Also, I've always sand blasted my fine wire plugs and they seem to last about 1000 hours.

 

They probably get blasted 10 to 15 times in their life. I always use glass beads in my cleaner which are pretty gentle, but I think this sand blasting thing is an old wives tail too..

 

I'm going to stick to clean spark plugs...

Ours had 130 hours and looked new, no lead fouling. There is a thin iriduim coating on those electrodes, and blasting them strips that coating.

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You don't need to get the expensive fine wire Tempest to get the performance. The Tempest massive electrode plugs use the same resistor used on the fine wire and perform equally well. Unlike the Champion massive plugs that show the football shape after 300 hrs the Tempest massive still round with no calibration required. The Tempest Fine Wire sell for $64.80 vs Tempest Massive $23.50. I had the Tempest massive for over a 1000 hrs with no problem at all and good EGT spread. I may be over cautious but I never liked that spot weld on the fine wire plug single electrode. At least on the massive you have three solid ground electrodes milled from the plug material, just my perception.

 

José

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I've gotten 1000 hours out of massive also. The only reason I'm using fine wires now is I found a screaming deal on EBAY.

 

I have looked all over the web and through the books I have, and I can see no credible indication that the electrodes on fine wire plugs are plated. That seems ludicrous! They would fail almost instantly weather sand blasted or not. The wear indications in the champion service manual show the width of the side electrode and the center electrode eroded by about 50% for the normal worn out condition, this would certainly have eaten through any plating, besides if they are plated, what are we paying so much extra for? It seems like a fine wire would be cheaper to make then massives if it only had a few micrograms of precious metal.

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