Why are my spark plugs disintegrated?

[zipper]

It does look like a heli coil type insert. I believe it was intended to stay in the head, when the plug was removed. Is there a history of a broken or stripped plug over the 400 hrs?

 

[tdonoughue]

You guys are exactly right. Don't know how I missed it (other than that I was looking at the tip, not farther down). Definitely that is an insert that is pulled out.

I don't know that the PO took as good a care of this one as you thought...

 

[JetboatBrad]

So that extra threaded section you’re seeing there is the helicoil from the first time it happened. It ripped the threads out. I pulled the injectors and they looked good. I just swapped them from one cylinder to another so I will see if it happens to be that. I’d buy another but it would be 2 weeks from Japan. I also got a bore scope and everything seems to look intact. The scratches you see in the center are from me scratching it with the scope. Can’t really see anything obvious out of the ordinary

 

[JetboatBrad]

It does look like a heli coil type insert. I believe it was intended to stay in the head, when the plug was removed. Is there a history of a broken or stripped plug over the 400 hrs?

No other problems other than this is the 3rd time it’s happened. It stripped the threads the first time

 

[zipper]

With that information...I would say do a compression and leakdown test on that cylinder, at least. That insert could be leaking during the compression/ignition part of the cycle, causing the buildup. The insert should have stayed in the head. Was locktite used?

 

[Weeb]

Is it still under warrants?

 

[JetboatBrad]

With that information...I would say do a compression and leakdown test on that cylinder, at least. That insert could be leaking during the compression/ignition part of the cycle, causing the buildup. The insert should have stayed in the head. Was locktite used?

It should have I know. The only reason it came out was because the spark plug end was deformed and slightly bulged when I took it out. The teeth on the insert generally anchor. I had to Use a little torque getting it out. I’m going back in with locktite

 

[JetboatBrad]

It should have I know. The only reason it came out was because the spark plug end was deformed and slightly bulged when I took it out. The teeth on the insert generally anchor. I had to Use a little torque getting it out. I’m going back in with locktite

Compression leakdown test I’m going to try next I guess

 

[JetboatBrad]

Is it still under warrants?

I don’t think so, unfortunately. I’m over on hours

 

[tdonoughue]

That orange color before the threads on the plug reminds me of the first plug you pulled out--where the hex part was all corroded. I wonder if the plugs were installed tightly enough. If they were not tight enough, gas could leak out of the threads. Also the incomplete connection to the block would inhibit heat dissipation.

Severe internet research also says to check the coil there for a loose connection, as well as for any anomalies in the boot (cracks, melted holes, etc.). The former can cause plug overheat; the latter can indicate gas escaping...

And, everyone says injectors. I have never pulled mine on the boat, so I don't know that I would be able to tell a good one from a bad one... Other than some obvious melted glob at the end or something. Can't really tell much from your photo except that there ain't no melted glob there...

 

[JetboatBrad]

That orange color before the threads on the plug reminds me of the first plug you pulled out--where the hex part was all corroded. I wonder if the plugs were installed tightly enough. If they were not tight enough, gas could leak out of the threads. Also the incomplete connection to the block would inhibit heat dissipation.

Severe internet research also says to check the coil there for a loose connection, as well as for any anomalies in the boot (cracks, melted holes, etc.). The former can cause plug overheat; the latter can indicate gas escaping...

And, everyone says injectors. I have never pulled mine on the boat, so I don't know that I would be able to tell a good one from a bad one... Other than some obvious melted glob at the end or something. Can't really tell much from your photo except that there ain't no melted glob there...

Thanks T. I pulled all 4 injectors and they looked identical. Clean and new looking. I have a new coil on the way. I swapped cylinder Coil 1 to 4 and visa versa. It did it again and no change. Obviously now I’m so torquing them with absolute precision. I went through all last time and replaced all. I’m thinking next I’ll swap everything from one engine to the next. Coils, plugs and injectors. After I try the pressure test

 

[Gym]

It may be as simple as the helicoil allowed the plug to sit too low in the cylinder causing it to burn up.

 

[JetboatBrad]

It looks like the plugs bottom out at the same spot on the head. The crush washer still stops at the head. The hole is wider but not wide enough for the plug to go in any further than the rest of them if that makes any sense.
I swapped the injector and tried to do a pressure test but the narrow plug hole wouldn’t allow the pressure tester to be tightened. I couldn’t get a 3/4” socket in there. But even with the injector swap, it’s doing the exact same thing.
My only conclusion is I’m getting detonation. I figured it would be much heavier ignition miss feeling but I guess not. The engine still runs with only a minimal small extra vibration and the demolishing of the plugs. Anyone ever have detonation on one of these engines?

 

[tdonoughue]

I would think you would hear knock if that were it. It is pretty hard to miss.

However, that said, the reasons for knock are the same as the reasons for the deposits on the plug--bad fuel mix (thus the suggestion of the injectors), timing off (thus the ECU bad suggestion)... only additional thing is low octane. Melting is caused by overtemp, bad fuel mix or timing off.

Common denominator seems to be ECU or fuel mix. If you have eliminated the injectors, you might have a bad ECU (either giving too much fuel, or messing up the timing)?

 

[mrcleanr6]

assuming your fuel is good, ecu is a definite possibility on this. it could be causing that cylinder to run lean causing detonation at higher rpms or as td said the timing could be off on that one cylinder causing the issue as well. i had a bad ecu on an mr1 in my wifes ski. that was causing the injectior to stay open longer than it was supposed to causing 1 cyl to run extremely rich. went through everything and nothing fixed it. new ecu and its been running great for the past 3 seasons.

 

[JetboatBrad]

I would think you would hear knock if that were it. It is pretty hard to miss.

However, that said, the reasons for knock are the same as the reasons for the deposits on the plug--bad fuel mix (thus the suggestion of the injectors), timing off (thus the ECU bad suggestion)... only additional thing is low octane. Melting is caused by overtemp, bad fuel mix or timing off.

Common denominator seems to be ECU or fuel mix. If you have eliminated the injectors, you might have a bad ECU (either giving too much fuel, or messing up the timing)?

Yea I hear no knock from the lower end for sure. It does make this funny noise from the back by the exhaust but it always has done that. Sounds like vibration hitting the rear of the engine compartment to me. They both make that sound at idle and low RPMs. Just worse now on that one engine, thought more vibration from detonation. I was thinking that the detonation is coming from the ground diode that broke off the original plug. I understand that things can embed in the head or piston. I’m at least gonna have to pull the head and inspect it I think.

 

[JetboatBrad]

assuming your fuel is good, ecu is a definite possibility on this. it could be causing that cylinder to run lean causing detonation at higher rpms or as td said the timing could be off on that one cylinder causing the issue as well. i had a bad ecu on an mr1 in my wifes ski. that was causing the injectior to stay open longer than it was supposed to causing 1 cyl to run extremely rich. went through everything and nothing fixed it. new ecu and its been running great for the past 3 seasons.

I’m gonna try a new ecu if I can’t see any debris. I think you might be right and I’m going to go that route and see if it fixes the problem. Thanks for the info. I never would’ve thought about that seeing as it’s only one cylinder.