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Spark plug failure?

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    Posted: September-09-2019 at 9:56pm
Anybody ever seen this before?




Is that spark plug failure? Should I try and vacuum out the cylinder, or do you think it is too late. The compression on that cylinder is 101 and the others range between 105 and 118.
1980 Ski Nautique Boat Bar
1988 Mastercraft Tristar Open Bow
1988 Mastercraft Tristar Closed Bow
1969 Seacamper Houseboat
1986 Harris Pontoon
2004 Seadoo GTX SC + Flydive Xboard
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: September-09-2019 at 10:06pm
It looks to me like you had detonation going in that cylinder.
That is normally caused by advanced timing or a vacuum leak making that cylinder run very lean. Advanced timing or lean burn create very high temperatures in that cylinder.
Another possible would be a mis fire between your plug wires making the plug fire at the wrong time. Look for halo's in the plug wire. A halo in a wire is proof of electricity escaping your wire and looking for another ground.
The ground electrode in your plug looks like it is melted back and the positive electrode is missing.
My guess would be it melted also.
Crank the engine over with no plug in the hole and compression should blow any pieces out. This may have happend when you did your compression check.

Look close at all your other plugs. They may point you towards a solution.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote seacamper Quote  Post ReplyReply Direct Link To This Post Posted: September-09-2019 at 10:28pm
Originally posted by MrMcD MrMcD wrote:

It looks to me like you had detonation going in that cylinder.
That is normally caused by advanced timing or a vacuum leak making that cylinder run very lean. Advanced timing or lean burn create very high temperatures in that cylinder.
Another possible would be a mis fire between your plug wires making the plug fire at the wrong time. Look for halo's in the plug wire. A halo in a wire is proof of electricity escaping your wire and looking for another ground.
The ground electrode in your plug looks like it is melted back and the positive electrode is missing.
My guess would be it melted also.
Crank the engine over with no plug in the hole and compression should blow any pieces out. This may have happend when you did your compression check.

Look close at all your other plugs. They may point you towards a solution.

I will put the timing gun on the boat when I put it in the water tomorrow and check for advanced timing. I will also look for a vacuum leak. Where do I start on that? What does a halo look like on a plug wire? I googled that with no luck.
1980 Ski Nautique Boat Bar
1988 Mastercraft Tristar Open Bow
1988 Mastercraft Tristar Closed Bow
1969 Seacamper Houseboat
1986 Harris Pontoon
2004 Seadoo GTX SC + Flydive Xboard
1999 Adventurecraft
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: September-09-2019 at 11:10pm
A halo is a small white circle around a spot where electricity is blowing out of a plug wire.
The circle is probably 3/8" or smaller but looks like a halo over the head of an angel in pictures.   If you see a halo you will recognize it.   It will be where a wire is sparking to another wire as they rub together or to another ground where the wire is close enough to rub or touch. It will not happen in open space.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JDD33 Quote  Post ReplyReply Direct Link To This Post Posted: September-09-2019 at 11:42pm
Fire it up one evening then turn off the lights. You'll see real quick what's not supposed to be sparking!!
Old school goin back to school!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 12:40am
Sometimes you can hear it ticking where the spark is jumping but we are getting ahead of the issue. Right now he still does not know what caused the plug to fail.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tryathlete Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 12:47am
Originally posted by MrMcD MrMcD wrote:

Sometimes you can hear it ticking where the spark is jumping but we are getting ahead of the issue. Right now he still does not know what caused the plug to fail.


Just in case Mr. Seacamper wants to check his spark plug wires three ways to Sunday, here’s a good instructional video;
YouTube is your friend
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MrMcD Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 1:20am
I looked for pictures of a Halo, did not find any but the halo is about the size of a small pencil eraser. You will see a faint white outline of the halo where it is sparking through the wire to ground. I have seen wires present this several times over the years.
The Youtube video gave a nice wire test for you also.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tryathlete Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 3:53am
Originally posted by MrMcD MrMcD wrote:

I looked for pictures of a Halo, did not find any but the halo is about the size of a small pencil eraser. You will see a faint white outline of the halo where it is sparking through the wire to ground. I have seen wires present this several times over the years.
The Youtube video gave a nice wire test for you also.


I could not find a pic of the halo effect either. That’s how I stumbled upon the instructional YouTube video. The spray bottle was novel!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 9:13am
I hope all your other plugs aren't that black.

What brand and part number are the plugs?

If that plug broke suddenly, then there are probably pieces embedded in the top of the piston and the cylinder head.

What made you decide to look at the plugs? and what do the others look like?

Like JDD33 said, fire it up in the dark, you'll know if there's spark where it shouldn't be
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Post Options Post Options   Thanks (0) Thanks(0)   Quote seacamper Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 10:05am
Originally posted by KENO KENO wrote:

I hope all your other plugs aren't that black.

What brand and part number are the plugs?

If that plug broke suddenly, then there are probably pieces embedded in the top of the piston and the cylinder head.

What made you decide to look at the plugs? and what do the others look like?

Like JDD33 said, fire it up in the dark, you'll know if there's spark where it shouldn't be

I am using Autolite copper 24 plugs gapped to .035. All the plugs are slightly blacker than I would like. I may be running too lean. I have to admit that I was surprised at how loose the plugs were when I pulled them out which could account for the breakage on the one plug according to this article:
Plugs
I decided to look at the plugs because it started running rough.
1980 Ski Nautique Boat Bar
1988 Mastercraft Tristar Open Bow
1988 Mastercraft Tristar Closed Bow
1969 Seacamper Houseboat
1986 Harris Pontoon
2004 Seadoo GTX SC + Flydive Xboard
1999 Adventurecraft
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gun-driver Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 10:07am
A loose plug will also do that, guess how I know.
My guess is that the electrode is already out the exhaust.

You are far from lean.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 10:37am
The black is either oil fouling or a rich gas mixture.at least from the pictures

Rich is light and fluffy and you can wipe or clean off a lot of the fluffiness, Oil fouling is shinier and won't wipe off.

Short of tearing things apart, I'd put in 8 new plugs and see how it runs and keep an eye on the plugs, especially the cylinder the pictured plug came from.

I had a plug slowly eat up the center electrode while the other 7 were fine. Only found it with a routine check of the plugs and my first hint that something might be wrong was that the plug was barely hand tight. A compression test was good and there were no flecks of aluminum from any kind of piston damage stuck to the plug. The plug "gap" was huge but it still fired. And the boat ran good

I gave it new plugs, a good hand over hand of the wires, made sure they were all tight and ran it.

At least in my case everything was good and it's still running good several years later.

Your gap is "extra huge" and with all that black it probably quit firing and caused some roughness..

If you don't have any signs of melted aluminum, I'd put in new plugs and run it with frequent checks as mentioned earlier.

I think the "blackness" is a separate unrelated issue like oil control or carburetor problems.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote seacamper Quote  Post ReplyReply Direct Link To This Post Posted: September-10-2019 at 12:56pm
Thanks guys! It is back together with new plugs. Now I am battling with the Racor 110 fuel water separator! I will start a new thread..
1980 Ski Nautique Boat Bar
1988 Mastercraft Tristar Open Bow
1988 Mastercraft Tristar Closed Bow
1969 Seacamper Houseboat
1986 Harris Pontoon
2004 Seadoo GTX SC + Flydive Xboard
1999 Adventurecraft
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