The Hull Truth - Boating and Fishing Forum

Go Back   >
Search


Reply
 
Thread Tools Search this Thread
Old 05-17-2010, 12:41 PM   #1
Admirals Club
Thread Starter
 
Join Date: Jun 2009
Location: Orlando
Posts: 1,048
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.
PelagicHunter is offline   Reply With Quote
Old 05-17-2010, 12:45 PM   #2
Admirals Club
 
Join Date: Feb 2008
Location: Virginia
Posts: 7,065
Default

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.
mobjack22 is offline   Reply With Quote
Old 05-17-2010, 12:52 PM   #3
Admirals Club
Thread Starter
 
Join Date: Jun 2009
Location: Orlando
Posts: 1,048
Default

so why would that noise be gone after i replaced the plug?
PelagicHunter is offline   Reply With Quote
Old 05-17-2010, 12:52 PM   #4
Senior Member
 
Join Date: Oct 2006
Location: Baton Rouge, LA
Posts: 2,079
Default

spun bearing or foreign material(s) either way not good.
hybrid is online now   Reply With Quote
Old 05-17-2010, 01:04 PM   #5
Senior Member
 
Join Date: Jul 2009
Location: Pacific NW Coast!
Posts: 550
Default

Carbon build up on the plug? Are all plugs like this or just the one?
heeerefishyfishy is offline   Reply With Quote
Old 05-17-2010, 01:07 PM   #6
Admirals Club
Thread Starter
 
Join Date: Jun 2009
Location: Orlando
Posts: 1,048
Default

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
PelagicHunter is offline   Reply With Quote
Old 05-17-2010, 01:13 PM   #7
Admirals Club
 
Join Date: Feb 2008
Location: Virginia
Posts: 7,065
Default

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
mobjack22 is offline   Reply With Quote
Old 05-17-2010, 01:15 PM   #8
Senior Member
 
Join Date: Jul 2009
Location: Pacific NW Coast!
Posts: 550
Default

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?
heeerefishyfishy is offline   Reply With Quote
Old 05-17-2010, 01:17 PM   #9
Admirals Club
Thread Starter
 
Join Date: Jun 2009
Location: Orlando
Posts: 1,048
Default

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
PelagicHunter is offline   Reply With Quote
Old 05-17-2010, 01:20 PM   #10
Senior Member
 
Join Date: Aug 2008
Location: Jupiter
Posts: 5,416
Default

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.
Capttater is offline   Reply With Quote
Old 05-17-2010, 01:22 PM   #11
Senior Member
 
Join Date: Nov 2006
Location: Lynnwood Wa.
Posts: 1,704
Default

Actually, this happens most frequently from detonation due to poor fuel.
prober is offline   Reply With Quote
Old 05-17-2010, 01:25 PM   #12
Senior Member
 
Join Date: Jul 2009
Location: Pacific NW Coast!
Posts: 550
Default

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?
heeerefishyfishy is offline   Reply With Quote
Old 05-17-2010, 01:26 PM   #13
Admirals Club
Thread Starter
 
Join Date: Jun 2009
Location: Orlando
Posts: 1,048
Default

nope, looks exactly the same. maybe a little darker on the rings, but thats it
PelagicHunter is offline   Reply With Quote
Old 05-17-2010, 01:26 PM   #14
Admirals Club
 
Join Date: Sep 2004
Location: Mechanicsville VA
Posts: 6,953
Default

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.
t500hps is offline   Reply With Quote
Old 05-17-2010, 01:27 PM   #15
Senior Member
 
Join Date: Aug 2008
Location: Jupiter
Posts: 5,416
Default

Quote:
Originally Posted by prober View Post
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.
Capttater is offline   Reply With Quote
Old 05-17-2010, 01:29 PM   #16
Senior Member
 
Join Date: Jul 2009
Location: Pacific NW Coast!
Posts: 550
Default

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.
heeerefishyfishy is offline   Reply With Quote
Old 05-17-2010, 01:29 PM   #17
Senior Member
 
Join Date: Jun 2007
Location: Magnolia Springs, Al,
Posts: 1,049
Default

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,,,
pappastratos is offline   Reply With Quote
Old 05-17-2010, 01:31 PM   #18
Senior Member
 
Join Date: Jul 2009
Location: Pacific NW Coast!
Posts: 550
Default

Quote:
Originally Posted by Capttater View Post
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...
heeerefishyfishy is offline   Reply With Quote
Old 05-17-2010, 01:36 PM   #19
Admirals Club
THT sponsor
 
Join Date: Aug 2005
Location: Venice, Florida
Posts: 16,368
Default

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.
Mr. Demeanor is offline   Reply With Quote
Old 05-17-2010, 01:38 PM   #20
Senior Member
 
Join Date: Mar 2008
Location: mass.
Posts: 5,455
Default

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.
On The Edge 1 is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off

Forum Jump


All times are GMT -7. The time now is 02:52 AM.


©2009 TheHullTruth.com

Powered by vBulletin® Version 3.9.3.0
Copyright ©2000 - 2016, Jelsoft Enterprises Ltd.