Spark Plug blew out of engine...ever seen it?

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Begester

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Has anyone ever heard of ?spark plug failure? on a boat? We had our 1989 Sea Ray 220DA with 5.7 Mercruiser out yesterday and had a spark plug fly out of the head (see attached photo). The failure appears to have occurred internal to the plug but it is likely that the plug was lose, as it came out of the head with only a few turns.

We had the boat out Saturday as well and it ran fine but on the way home it felt like I had a little bit of hesitation that felt like bad fuel, so I didn?t think much of it. Aside from this there were no warning signs.

Has anyone ever had this issue before? I?m heading back to the boat this afternoon with a new spark plug but before I run it too much, I?d like to see if there is anything else I should look at. I?m not 100% sure if the threads for the spark plug are stripped or not, but assuming I can get the plug in, is there anything else I should keep an eye out for? I started it up for ~10 seconds and there was definitely compression coming from the spark plug hole?
 

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Bondo

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Ayuh,... I've seen that happen a few times with Champion spark plugs,...

Never an AC though,...
 

HT32BSX115

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Has anyone ever heard of “spark plug failure” on a boat? ......................

I’m not 100% sure if the threads for the spark plug are stripped or not, but assuming I can get the plug in, is there anything else I should keep an eye out for? I started it up for ~10 seconds and there was definitely compression coming from the spark plug hole…

It's not uncommon at all. It *could* be "caused" by detonation (or a result of mild detonation) which can be caused by bad or contaminated fuel.

That plug appears like the threads are still intact but rusty (because it was only "held in by a thread" or two) more than likely it just backed out from vibration because it was loose to begin with.

I also wouldn't leave them in long enough to get rusty............... spark plugs are fairly inexpensive.

Looks like you might want to replace all your plugs.
 

wrench 3

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It wasn't uncommon around here in automotive small block Chevys. A combination of road salt and lack of maintenance.
Your problem is probably some what similar.
 

JoLin

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That plug appears like the threads are still intact but rusty (because it was only "held in by a thread" or two) more than likely it just backed out from vibration because it was loose to begin with.

Happened in my 1964 Dodge Polara (318 V-8) in 1972. My own fault. The plug wasn't torqued tight enough. Made a helluva racket going down the street. My girlfriend of the time slouched down in the seat so nobody would recognize her. I eventually got rid of both the car and the girl.

But, I digress... :focus:
 

Scott Danforth

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With the plug not tight, it couldnt transfer heat to the head.

Replace all the plugs
 

Will Fish

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Happened to me when I was on a sea trial for a boat I was thinking of buying. Looking at motors at dock I asked "when was the last tube up" because plugs and wires looked like they hadn't been changed in some time. Sure enough put out of marina start to put throttles down and bang. Good thing for 2 motors in that boat. And needless to say I did not purchase.

Maintenance on a boat is as important as changing your underwear, you shouldn't turn them inside out to get extra wear.
 

Silvertip

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Take a good look at the metal shell of the plug. It is discolored, rusty and the crimp for the electrode failed. I've seen this happen many times and it was always due to a gazillion heat/cool cycles (translated = lack of maintenance). The last one I saw was on a Oldsmobile Bravada SUV that happened to be owned by my fishing buddy. 13 years without a plug change makes conditions ripe for this to happen. You are very fortunate to be able to get the shell out of the head. In his case, three other plugs broke off in the head while trying to remove them.
 

Nbaas

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Had this happen today with an AC plug! had to limp back to the dock with one cylinder open. Loud and gassy. threaded part of the plug is still in the engine. other than the noise and the gas/air mixture spewing out of the engine, no other issues. investigating with a scope and doing a compression test tomorrow to see if any damage was done.
 

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poconojoe

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Not boat engines, but those Ford Triton engines threw spark plugs left and right. Ford wouldn't make good for it either.
It was a common problem.

Someone I knew had a Ford E250 van and one shot out. The plug was laying on the intake manifold and parts of the coil pack were strewn about.

Good luck getting that head drilled out and heli-coiled! There was almost no access in that van.
How do you pull the engine in an E250 anyway? Lift off the body?
 
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