cracked spark plug insulator

[vic syracuse]

This is something I have never seen before. This plug came out of the lower position in number 2 cylinder on my RV-10. It is the Unison UREM38S fine wire plug with about 500 hours on it. REcently I noticed an intermittent miss ONCE in a while. Nothing I could put my fingers on. About a month ago I noticed number 2 cylinder rising quickly to 1420 degrees EGT on takeoff. Normal is low 1300's. I pulled the power back and the EGT appeared to settle out normally, and behaved and looked normal for the rest of the one hour flight. I did reach in and pull out the number 2 injector on the preflight the next morning and blew through it just in case there was some blockage. I had sonic cleaned the injectors a week earlier. The subsequent takeoff had normal EGT readings, as did many after that. I assumed whatever had caused the abnormal indications was long gone. It was only because I was installing the Aerosplat air-oil separator and I had the cowling down that I happened to check the lower plugs. I had just cleaned them about 10 hours earlier.

As a precaution I have replaced all lower plugs, as I do fly at night and we are going back to Alaska this summer.

Vic

[mannanj]

Obviously you haven't made the proper sacrifice's to the ceramics gods lately! If you're contrite enough, buy several sets and donate them to your friends. my address is: .......:

[aerhed]

Good thing that sucker didn't bing bong around in your jugs.

[rocketbob]

Sounds like you just found out that spending $65 on a plug doesn't buy you anything better than a decent $2 automotive plug.

[RV10inOz]

Vic,

That is very interesting indeed.

I would really like to see the engine monitor data file if you can email it to me.

I assume you did not see any irregular CHT rises which would indicate pre-ignition from the exposed tip. But that is almost certainly what you would have had before long.

Have you ever dropped even from a small height one of the plugs? Also how do you clean them?

This is the puzzling question though, the rise in EGT was because that plug stopped firing, it was shorting out somewhere through the crack. How did it come good again?

Lucky that it did not become a costly experience. Engine monitors should not be treated lightly when they tell you something. This is why I strongly encourage people to do the APS training.

[Don Patterson]

The EAA had a Webinar on plugs a few months ago and talked about the cracking of ceramics on Champion plugs.
A Google search will take you to the video.

[Rockyjs]

We did an annual last Feb on an SR-22 IO-550. One of the plugs had 3 cracks and another plug had half the insulator missing. We boroscoped the cylinder and found no damage. One was located on the top of one cylinder and another one was located in the bottom on another cylinder. Data logs were pulled and the engine experience no catastrophic event over 70 hours. The aircraft had a total of 350 hours and had plugs changed at previous annuals. No reason was given for the previous plug swap. I searched and found many problems with the cracking insulation. We recommended removal of all the plugs and re-installed mass electrodes in there place.

[vic syracuse]

[quote=RV10inOz;738570]Vic,

I would really like to see the engine monitor data file if you can email it to me. I need to figure out how to get it out of the AFS 3500 and I will do that.

I assume you did not see any irregular CHT rises which would indicate pre-ignition from the exposed tip. But that is almost certainly what you would have had before long. Nope, no irregular CHT issues.Have you ever dropped even from a small height one of the plugs? Also how do you clean them? No, never. Very careful with plugs. I do blast clean them as per the care instructions from Autolite.This is the puzzling question though, the rise in EGT was because that plug stopped firing, it was shorting out somewhere through the crack. How did it come good again? That's very interesting to me as well. I feel very lucky that I had a few extra minutes and decided to check the lower plugs while the cowling was off.

These were the Autolite, not Champion fine wire. I like using the fine wire on the lower plugs as they never seem to foul. The massive plugs seem to be more prone to lead fouling on the ground, even though I've always aggressively leaned while on the ground.

[Vlad]

Dropped a spark plug recently $25 loss

[ccsmith51]

I dropped a plug once, and then figured as clumsy as I am the $29 magnetic plug wrench from ACS would have almost paid for itself. I have one now...