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Old 05-17-2010, 11:41 AM
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Default What Would Cause a Spark Plug GAP to close

i was pulling the plugs on my motor after noticing some vibration and a rattling sound coming from the motor, found that one of the six plugs , the gap between the electrode and the tip had closed. its supposed to be 0.4 mm , but the gap was closed where the tip was touching the electrode.

after i replaced the plugs the motor ran fine and that sound was gone.

what would cause that gap to close like that? im pretty sure i didnt install it like that as i always check the gap.
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Old 05-17-2010, 11:45 AM
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When that happened to me it was because I had lost a ring and the piston "slapped" the plug. My motor ran and sounded fine at the dock but only had about 3/4 power. Had to rebuild it.
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Old 05-17-2010, 11:52 AM
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so why would that noise be gone after i replaced the plug?
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Old 05-17-2010, 11:52 AM
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spun bearing or foreign material(s) either way not good.
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Old 05-17-2010, 12:04 PM
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Carbon build up on the plug? Are all plugs like this or just the one?
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Old 05-17-2010, 12:07 PM
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no, all the plugs are fine without any carbon, its just that the gap is closed on this plug. once i replaced it all the symptoms were gone. just dont know why the gap was closed on this one plug
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Old 05-17-2010, 12:13 PM
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The piston can still travel for a while until it finally tears itself up and stops the motor... Have you run the boat? Did it have full power? Be careful
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Old 05-17-2010, 12:15 PM
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Check the obvious stuff first.

Is that plug with the closed gap te exact same part / part number than the rest of the plugs? Or does it have a longer reach?
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Old 05-17-2010, 12:17 PM
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yes same gap, same plug, ngk brk6e, gap was closed, motor was shaking and making a noise, replace the plug, motor ran fine.

cant figure out why that gap would close
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Old 05-17-2010, 12:20 PM
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Loose piston on one end or the other of the rod. I had one run for about 20hrs like that. Finally the rod came through the block.
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Old 05-17-2010, 12:22 PM
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Actually, this happens most frequently from detonation due to poor fuel.
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Old 05-17-2010, 12:25 PM
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Quote:
Originally Posted by PelagicHunter View Post
yes same gap, same plug, ngk brk6e, gap was closed, motor was shaking and making a noise, replace the plug, motor ran fine.

cant figure out why that gap would close
This is bad dude...

I don't mean to freak you out but I would loose sleep over this.

Put in a new plug and monitor it. Does the plug with the closed gap look any different from the rest of the plugs?
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Old 05-17-2010, 12:26 PM
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nope, looks exactly the same. maybe a little darker on the rings, but thats it
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Old 05-17-2010, 12:26 PM
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Anything closing that gap is not good......test running it (under load) are re-checking the plug is needed. Be careful, it could need a simple re-build now, or a complete new block, etc after tearing it up further.
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Old 05-17-2010, 12:27 PM
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Quote:
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Actually, this happens most frequently from detonation due to poor fuel.
Causing a plug gap to close? I guess if it ignited from the piston side you could have something there.
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Old 05-17-2010, 12:29 PM
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Keep checking the dumb things first.

Who put the plugs in? Did they drop it or knock it against something before putting it in?

Replace, take 'er out for a rip and get back to us.
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Old 05-17-2010, 12:29 PM
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Actually, this happens most frequently from detonation due to poor fuel.
sounds better than :
Loose piston on one end or the other of the rod.
You could take the head off & check piston.
I take this is a 2 stroke,,,
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Old 05-17-2010, 12:31 PM
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Causing a plug gap to close? I guess if it ignited from the piston side you could have something there.
Yea this is new to me too. I figure detonation would have equal pressure on all sides of the negative terminal of spark plug...
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Old 05-17-2010, 12:36 PM
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Quote:
Originally Posted by heeerefishyfishy View Post
Yea this is new to me too. I figure detonation would have equal pressure on all sides of the negative terminal of spark plug...
You would think but I have seen this happen as well.
Look deep around the porcelain insulator fro little shiny specs of aluminum.
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Old 05-17-2010, 12:38 PM
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Piston hit it. Tear it down now for short money or wait till a bigger problem shows it's ugly face and pay more later.
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