Sparkplug wire replacement

by Alan Arnold in 912 / 914 Technical Questions 6 years ago

I need to replace my sparkplug caps for the second time. With 830 hours and 12 years of operation and no other problems, I am wondering if there is a reason to also replace the wires. The caps are failing at the sparkplug interface only and I can see nothing wrong with the wires. I'm just wondering if it would be prudent to do this during the annual condition inspection I'm starting today or are the wires normally good to go to TBO?

Alan

Re: Sparkplug wire replacement

by Rob Seaton » 6 years ago

Rob Seaton

3 1.32k 240

The question is why are they failing? They should go to 2000hrs no problem, I have seen some with 3600 hrs, on flight school engines no less...
Maybe you have a pitted gearset causing very high vibrations? You can test this by having your prop dynamically balanced; if the tech throws his hands up after moving the trial weight 3 times, and it still wants it moved, your gearset is shot.
-Or you are smacking the cap with your hand every inspection? (bending the prong and wearing out the spring inside the cap)

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Re: Sparkplug wire replacement

by Alan Arnold » 6 years ago

Alan Arnold

20 188 145

Thank you for your reply Rob. I had my 600 hour gearbox inspection done by Lockwood at 400 hours because I was using a Warp Drive prop and found out it was too heavy. There were no problems found. My new Whirlwind prop was balanced not long after that. My carbs are properly synced using gauges. Both times I have had a cap become loose at the plug it was on a bottom plug that I can't touch without removing the bottom cowl, so the bottom caps are rarely touched. If one cap goes bad I change all. The first time I just changed the bad cap and shortly afterwards another bottom cap failed, so new caps all around this time. I will get my prop balanced soon because of your suggestion.

Thanks again.

Alan

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Re: Sparkplug wire replacement

by Alan Arnold » 6 years ago

Alan Arnold

20 188 145

So here I am finishing up my annual. I cut the faulty sparkplug cap open, rubber boot only. Only one side of the spring clip was visible. "Aha" I said. Then I looked closer. Only one side is supposed to contact the sparkplug threads. The supposedly damaged cap is perfectly intact except for the sliced open rubber boot. Apparently the dumbass mechanic, me, can't properly install some of those bottom plug caps. They are fairly hard to access. A couple of them anyway. That's probably what happened the first time as well.

I might be able to remember to be more careful in the future. Maybe.

Alan

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Re: Sparkplug wire replacement

by Robert Elves » 3 years ago

Robert Elves

0 6 17

No life limit on sparkplug wires, they are an on condition. Try not to twist bend or pinch which can damage them. Found my sparkplug caps failing after 15 years and 1100 hrs so replaced them all. If you have one or two break with higher years and time, would recommend replacing all and carry a spare. If you see an rpm drop on ignition check, check plugs/wires first. A loose plug in flight grounding on engine will feel like an engine stall. Land as soon as practical. - LSRI/9-series Maintenance IRMT/“Gold Seal” CFI

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Sparkplug wire replacement

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