Plug replacement

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Rich
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Plug replacement

Post by Rich »

My plugs are the Unison/Autolite fine-wires: UREM38S. They are now 13 years and just over 850 hours of use - something north of 60 million spark events for each. There has been a bit of annoying vibration on and off for the last year (pre- and post- Surefly) and I'm thinking of replacing them at annual later this month. Even if they are not the root of this vibration I figure it's time. The logical replacement would be the Tempest plugs rather than Champion, as the latter has had some real manufacturing problems of late.

Does anyone have recent experience with the current fine-wire offerings?
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Rick
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Re: Plug replacement

Post by Rick »

I installed the Tempest REM38S fine wire plugs back in 2012, nearly 1000 hours ago, and they are still like new. I clean the little bit of carbon out of the bases at each annual, and that's it. I have no idea what the life expectancy is on the fine wires - any thoughts? I suppose they do wear out eventually, even if you take care of them. I would never go back to the 'regular' plugs.
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Re: Plug replacement

Post by Rich »

Thanks, Rick. Mine have also performed well all this time. They never foul and just get cleaned at each annual. One additional rationale for replacing them is that with the Surefly half the plugs "spark" twice as much per hour as before, hence overall I have 50% more spark (though not ignition) events per hour than historically.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Steve
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Re: Plug replacement

Post by Steve »

Rich:

I installed the Tempest UREM38S fine wire plugs about 300 hours ago. They look new, and all I have to do at annual is pick the occasional lead deposit out of the insulator recess. I have been very happy with them (except for the co$t).

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Re: Plug replacement

Post by Chris B »

If ...
  • Resistance checks OK (typically ~1k, <5k Ohms max)
  • No significant "rounding" of the tips or enlarged gap
  • Threads are in good shape
  • No ceramic cracks
... I clean them and keep them running.

Here are the bottom plugs that I pulled on Saturday before cleaning.
Number 2 and 3 have about 1800 hrs. 8-)

Image
Full resolution: https://i.imgur.com/Cf1hVSy.jpg

Chris
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Davestation
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Re: Plug replacement

Post by Davestation »

I’ve always gone with the tempest. I don’t think I’ve ever replaced a fine wire due to wear. A few due to high resistance.
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Re: Plug replacement

Post by Rich »

Under the heading of "If it ain't broke":

Replaced all 8 plugs with the Tempests. Initial flight went great - for a few minutes. Then problems arose. To condense what I experienced:

It was one or more (I suspect more than one) Tempest plugs being driven by the Surefly. The usual diagnosis wouldn't allow me to pinpoint which plug(s). The engine was a-shaking and I couldn't readily see any anomalies with EGTs when running on the SIM.

I could not reproduce the problem on the ground. Normal runups, high power runups, before and after problem flights. Lengthy singe-mag operation on the ground. I made three separate flights and always, right about 6-ish minutes after takeoff, problems cropped up. This was no mild roughness. Bucking and shaking. It kind of came and went, but was mostly there.

I did note on one flight that #2 and #4 EGT's jumped up on descent. I checked cold resistance of these plugs on the ground and they were a little flaky, so for one flight I replaced these 2 with Unisons we had removed. But the problem repeated itself on the subsequent flight.

The fix is to put the previously removed Unisons back in the plane for plugs that are fired by the Surefly. The Tempests are still in place for the right mag (the Slick). Everything is fine in this condition.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: Plug replacement

Post by Davestation »

I don’t think Unison exists anymore, Tempest bought them a while back, I would think it’s the same plug as long as you’re using the same P/N. Did you test the new tempest? Maybe an infant mortality thing. I have come across a few plugs that were very high resistance straight out of the package.
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Re: Plug replacement

Post by Rich »

Davestation wrote: Tue Aug 11, 2020 11:50 pm I don’t think Unison exists anymore, Tempest bought them a while back, I would think it’s the same plug as long as you’re using the same P/N. Did you test the new tempest? Maybe an infant mortality thing. I have come across a few plugs that were very high resistance straight out of the package.
You are correct. Tempest bought the product line from Unison and as far as I know, they are the same design and manufacturing process.

We didn't test beforehand. After the first flight I pulled them and checked resistance in the 4 suspect plugs. The ones for #1 and #3 showed ~ 950 ohms. #2 and #4 gave flakey readings. They would show about the same, but then jump to 2000-3000 ohms. But still I had problems when I had Unisons in #2 and #4 and the Tempests that showed OK in #1 and #3.

I initially thought it was infant mortality, but every subsequent flight showed the same behavior if I had any of these particular Tempests being fired by Surefly. Runups and initial climb-out fine until a few minutes into the flight. I suspect heat-related problems. The closest correlation I could make is to CHTs coming up to normal operating temperature.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Re: Plug replacement

Post by Davestation »

Plugs generally start around 1k and slowly climb to that limit of 5k. Maybe the surefly doesn’t like “old” plugs and those two just started their life on the edge. Did you check the resistance of the old ones that it liked?
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