Do all spark plug gaps need to match if within range?

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smoss
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Do all spark plug gaps need to match if within range?

Post by smoss »

I just purchased a new set of Tempest UREM38S fine wire plugs, replacing my last set of Unison UREM38S plugs preventatively, as they've had a hard life and been beat up by a lot of mechanics, and I was feeling paranoid. The recommended gap is .017 - .021, and they are supposed to be pregapped out of the box. Most all of them are a very tight .017 (more like a .016, but then perhaps my cheap feeler gauges are off), but one of them is a .019 or .020. My last set never really eroded at all, with the gaps never getting bigger, so setting at the lowest end isn't really an issue. My question is, with the fine wires being so touchy to adjust (see http://www.diamondaviators.net/forum/fi ... t3810.html), does it matter if I have 1 plug in a cylinder with a low end gap, and another with a high end gap? Will that adversely affect engine running, or is the difference entirely negligible, and I shouldn't risk breaking the plug?
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Re: Do all spark plug gaps need to match if within range?

Post by CFIDave »

For what it's worth, when I installed new Tempest fine-wire plugs in our DA40 last summer I didn't touch the gaps -- partly because I didn't want to risk weakening the electrodes.

The good news is that the engine runs just as well without re-gapping.
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Re: Do all spark plug gaps need to match if within range?

Post by smoss »

Dave, did you check the gaps at all?
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Re: Do all spark plug gaps need to match if within range?

Post by CFIDave »

smoss wrote:Dave, did you check the gaps at all?
No
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Gasser
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Re: Do all spark plug gaps need to match if within range?

Post by Gasser »

Just ordered my fine wire plugs and new copper gaskets.

Where do I find torque specs? If anybody has them to save me time that would be awesome.

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Re: Do all spark plug gaps need to match if within range?

Post by smoss »

35 ft-pounds as per the Diamond maintenance manual (downloadable from their website). See also the attached Unison (now Tempest) spark plug guide.
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Unison spark plug guide.pdf
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