The Boating Forum - What Would Cause a Spark Plug GAP to close

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PelagicHunter
05-17-2010, 11:41 AM
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.


mobjack22
05-17-2010, 11:45 AM
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.

PelagicHunter
05-17-2010, 11:52 AM
so why would that noise be gone after i replaced the plug?


hybrid
05-17-2010, 11:52 AM
spun bearing or foreign material(s) either way not good.

heeerefishyfishy
05-17-2010, 12:04 PM
Carbon build up on the plug? Are all plugs like this or just the one?

PelagicHunter
05-17-2010, 12:07 PM
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

mobjack22
05-17-2010, 12:13 PM
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

heeerefishyfishy
05-17-2010, 12:15 PM
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?

PelagicHunter
05-17-2010, 12:17 PM
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

Capttater
05-17-2010, 12:20 PM
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.

prober
05-17-2010, 12:22 PM
Actually, this happens most frequently from detonation due to poor fuel.

heeerefishyfishy
05-17-2010, 12:25 PM
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?

PelagicHunter
05-17-2010, 12:26 PM
nope, looks exactly the same. maybe a little darker on the rings, but thats it

t500hps
05-17-2010, 12:26 PM
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.

Capttater
05-17-2010, 12:27 PM
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.

heeerefishyfishy
05-17-2010, 12:29 PM
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.

pappastratos
05-17-2010, 12:29 PM
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,,,

heeerefishyfishy
05-17-2010, 12:31 PM
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...

Mr. Demeanor
05-17-2010, 12:36 PM
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.

On The Edge 1
05-17-2010, 12:38 PM
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.

heeerefishyfishy
05-17-2010, 12:40 PM
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.

Well said.

But with no other symptoms ... could it be the installer messed something up?

Is the spark plug supposed to have a washer?

rwidman
05-17-2010, 12:47 PM
Well said.

But with no other symptoms ... could it be the installer messed something up?

Is the spark plug supposed to have a washer?

He didn't specify if the motor had been running fine and developed a rattle and vibration or if this happened immediately after the spark plugs were replaced or checked.

The answer to that question is important.

gw204
05-17-2010, 01:10 PM
Is the spark plug supposed to have a washer?

Yes.

PelagicHunter
05-17-2010, 02:03 PM
He didn't specify if the motor had been running fine and developed a rattle and vibration or if this happened immediately after the spark plugs were replaced or checked.

The answer to that question is important.

the motor was running fine, i changed out the water pump and put the motor on a hose, it peed fine, but it was vibrating ( i had noticed vibrating from the last trip) so i heard this rattling noise, checked the lower unit, everything fine, pulled the plugs, one had been bent. changed the plug, then motor ran fine

heeerefishyfishy
05-17-2010, 02:08 PM
Moderately related but a cool video anyways:

http://www.youtube.com/watch?v=sEf8va1S7Sw&playnext_from=TL&videos=2wqj61Uutrc

Dale/Ga
05-17-2010, 02:09 PM
this same thing happened to me 2 years ago on a 94 Johnson 112. I replaced the plugs and went fishing. no problems since. at 16 yrs old when it turns loose it will be time for a new one.

rwidman
05-17-2010, 02:44 PM
the motor was running fine, i changed out the water pump and put the motor on a hose, it peed fine, but it was vibrating ( i had noticed vibrating from the last trip) so i heard this rattling noise, ................

Read that statement slowly.

The way I read it, the motor began vibrating at some time in the past. It had nothing to do with you changing the water pump.

I suspect the vibrating started at the exact time when the spark plug became bent and the plug shorted. A multi cylinder engine is going to vibrate if one cylinder is not firing.

You have two choices; Take it to a mechanic, explain to him in detail, exactly what happened and when and have him take it apart and inspect it, or run it and see what happens. You might want to make sure your towing insurance is up to date.

jeffnick
05-17-2010, 03:13 PM
Did you compare the closed gap plug to the others to be sure it wasn't the plug electrode that is the problem? Did the electrode show any signs of impact...a flat spot or gouge? I'd pull the plug and shine a light in to see what that area of the top of the piston looks like, maybe run a compression test. If all that is good, I'd probably run it easy for a spell to see if anything else develops -- unless you fish offshore or like to pull water toys and need to work it hard, then more drastic measures would be in order to regain confidence in the motor.

billinstuart
05-17-2010, 05:18 PM
Is that one of those engines where the electrode has to be "clocked" to prevent damage??

Capttater
05-17-2010, 05:34 PM
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,,,
Doesn't it. I found my loose piston by pulling the plugs and pushing them with a dowel. Prior I looked in and turned the flywheel and saw it not moving like the others, it delayed more at the top and bottom than the rest.

slickster
05-17-2010, 05:37 PM
There is/was a foreign body in the cylinder at one time....could be a piece of piston, something sucked up the intake, best to pull the plug and check it with a bore scope....do it soon...

nautiduck
05-17-2010, 06:18 PM
There is/was a foreign body in the cylinder at one time....could be a piece of piston, something sucked up the intake, best to pull the plug and check it with a bore scope....do it soon...


Finally someone with some sense. Before you listen to all the armchair quarterbacks and have your engine torn down needlessly, find a mechanic with a scope to look and see if you have any marks on the piston. Any impact will leave some kind of mark. Also are you sure the right plug was used? Ive seen one wrong length plug installed by accident before. Was the arm mashed down against the center electrode? Your electrode in the center of the plug could have come loose as mentioned above. Plugs do at times need to be regapped, they can change. As far as the noise as rwidman said any engine with a cylinder missing is going to make some odd noises. When the cylinder fires the compression pushes the piston down, when it misses the crank pulls it down changing the dynamics of how the engine sounds. Down get into panic mode as of yet, it may be youve already taken care of the only issue.

t500hps
05-17-2010, 06:39 PM
A few years ago I had concerns about one of my engines and bought a bore scope to see what was going on. It is a camera that fits inside the spark plug hole to see what the cylinder walls and piston top looks like.....considering you smashed the plug I'd really like to know what is going on in there.


BTW: mine turned out fine, hope yours does too.



EDIT: Just saw slickster recommended the same thing

itwonder
05-17-2010, 07:06 PM
In addition to borescope inspection, take an oil sample and send it in for analysis. Change the oil filter. Cut the old one open, straighten out the pleats and inspect with a magnifying glass for metal.

prober
05-17-2010, 10:46 PM
I have also seen a chunk of carbon bust loose and cause this, but it also bent a valve and sounded like a rod bearing had spun. Very loud knocking sound.

I used a top cylinder lube like a shock treatment of seafoam and it dissolved the carbon, knocking went away and a new plug had the engine running fine again. No more noise and just the slightest misfire. At least for another 30,000 miles at which time I rebuilt it and discovered the bent valve.

PelagicHunter
05-18-2010, 04:11 AM
UPDATE :

so i went to the marina yesterday and put the boat in the water, turned her on, and she just purrs ....took the cowling off, still no problems.....no sound, no vibration (in idle) everything sounded good. so i decided to take her for a little spin , still motor ran great w/o any vibration or noise.

just to be safe, i loaded her on the trailer and i took her to a mechanic, we hooked her up to the muffs and ran her, still no noise, so he put his stethoscope up to the cylinder and he doesnt' hear anything.

it was late last night so we didnt do much more than that, but today were gonna pull the plugs and do a compression test.

mobjack22
05-18-2010, 04:35 AM
Great News, fingers crossed for comp. check!

crothers
05-18-2010, 05:25 AM
My opinion ( I hate saying that) based on a 30yr career in engine engineering is the plug was hit by the piston or something that passes thru the cyl (pc of reed valve, carbon or ?), or the plug was wrong reach to begin with.
Plugs wear and the gap goes up with time, not closing.
Detonation or spark knock will not close the gap and are indicated by bright "speckles" evident on the piston crown.
A closed gap is usually a precursor of pending total failure in the piston/rod/brg assy and common with aluminum connecting rods that strectch over time. With steel rods, usually the rod bearing is giving it up.
Hopefully, you have the miracle of something passing thru the chamber and out. We shall see.

Mr. Demeanor
05-18-2010, 05:39 AM
A strap that is hit by the piston is rarely just bent closed.
I would check your reed valves.

PelagicHunter
05-18-2010, 05:41 AM
what would cause the noise to disappear when i changed the plugs?

PelagicHunter
05-18-2010, 05:44 AM
I have also seen a chunk of carbon bust loose and cause this, but it also bent a valve and sounded like a rod bearing had spun. Very loud knocking sound.

I used a top cylinder lube like a shock treatment of seafoam and it dissolved the carbon, knocking went away and a new plug had the engine running fine again. No more noise and just the slightest misfire. At least for another 30,000 miles at which time I rebuilt it and discovered the bent valve.

the noise is completely gone. i don't understand the theories of bent valves and broken rings and cylinders hitting the plug, then why is that noise completely gone ?? thats whats buggin me

Mr. Demeanor
05-18-2010, 05:53 AM
I assume the noise was your engine running rough because it wasnt firing on that cylinder.

PelagicHunter
05-18-2010, 06:03 AM
I assume the noise was your engine running rough because it wasnt firing on that cylinder.

i agree. the compression test today will reveal all

grin
05-18-2010, 08:07 AM
I can't believe noone has suggested a compression check. That would be a good idea. If the piston is cracked/ chunked, or a chunk of ring let loose, a compression check will maybe show you something. if it does and you fix it now it will probably be alot less painful than if the piston completely lets go. I would assume something got in between the piston and the plug, not good! Or possibly a rod bearing is gone/ close to gone/ ??? and the piston actually hit the plug. Something hit it! Or it was put in that way. No detonation or anything similar will cause that. 1st step is a compression check. If it passes that I'd still be scared. Maybe pop off the head to see if the piston has any pings in it. if something was in there the top of the piston will be pinged/nicked up. That's a scary symptom!

TTaxi
05-18-2010, 08:23 AM
Equal power is being produced by all cylinders now the new plug is firing.
As someone mentioned before , it could be that plug may have been dropped just before installation unless you know it was running well with the same plug earlier. Is the bent plug that was removed the exact same mfgr & number as the others and new one? (Same length in the engine?)

conehead39
05-18-2010, 08:34 AM
could be high carbon build up and a piece of carbon broke off and got between the ground electrode and the top of the piston.
Check compression, too high =carbon buildup.
Non uniform reading on that cylinder vs the others.
higher comp than others carbon buildup in that cylinder.
lower comp than others,,,,, piston may be cracked like between top ring and piston dome.

Did your ever seriosly over rev it and maybe floated the valves,
Valve spring gone bad .

center electrode somehow loosen and moved down.

Like someone said ,you could have dropped it.

rwidman
05-18-2010, 08:43 AM
..............As someone mentioned before , it could be that plug may have been dropped just before installation unless you know it was running well with the same plug earlier.

He posted that the engine was running fine, then developed a vibration. I think that's important information when troubleshooting.

It was mentioned above that the center electrode on the plug might have come loose and touched the other electrode. Examining the plug and comparing it to the others would confirm or deny this possibility.

YMMV
05-18-2010, 08:53 AM
so why would that noise be gone after i replaced the plug?

Your motor was misfiring causing the vibration and noise. Since you replaced the plug, it stopped missing.

Compression test will let you know if a ring is bad or if there is something with the head. It is also possible that there is carbon deposits and it broke loose.

PelagicHunter
05-18-2010, 08:58 AM
Your motor was misfiring causing the vibration and noise. Since you replaced the plug, it stopped missing.

Compression test will let you know if a ring is bad or if there is something with the head. It is also possible that there is carbon deposits and it broke loose.

yes i agree, i just wanna know theres not sometime more that im missing which can cause major problems down the road

ericinmich
05-18-2010, 09:46 AM
I'd hope you bumped it while putting it in.. if not, get the checkbook ready.

I wouldn't expect it could come from spark knock.

rwidman
05-18-2010, 10:01 AM
I'd hope you bumped it while putting it in.. if not, get the checkbook ready. .........

Go back and read all the posts. :roll

seaox230c
05-18-2010, 10:02 AM
You should be able to remove the spark plug that was hitting, shine a bright flashlight into the hole and hand crank the motor until the piston comes up. You should be able to see the damage if any ,fairly easily.

Hawkeye
05-18-2010, 10:08 AM
Maybe something, bolt, screw or nut and got sucked thru the air intake? I had it happen on a street rod with a BB chevy one time long ago.

ss3964spd
05-18-2010, 10:59 AM
Logic suggests that if it were caused by excessive clearence at the rod small end (someone said loose piston?), at the rod big end (worn bearing), or a stretched rod then it would have happened again and likely done so immediately. The only possible exception is that the plug ground strap that got hit was indexed in such a way that placed it close to the piston crown, and the replacement plug is indexed so that the strap is farther away.

Draw a line with a sharpie along the damaged plugs' insulator that is in line with the ground strap. Re-install it and note the lines' orientation with something adjacent on the engine. Remove. Mark a bunc of other plugs with the same line and install/remove them in the suspected cylinder until you find one that lines up like the damaged plug did. Install the rest of the plugs and fire the engine.

Internal engine parts don't magically tighten up again so if it's some loose parts flopping around the new indexed plug will get hit.

Dan

thundertrout
05-18-2010, 11:57 AM
same thing happen to me also.changed the plug out and ran it. kaboom!
this was a 225 evinrude.don't run it pull the head and take a peek.

Hawkeye
05-18-2010, 12:33 PM
Logic suggests that if it were caused by excessive clearence at the rod small end (someone said loose piston?), at the rod big end (worn bearing), or a stretched rod then it would have happened again and likely done so immediately. The only possible exception is that the plug ground strap that got hit was indexed in such a way that placed it close to the piston crown, and the replacement plug is indexed so that the strap is farther away.

Draw a line with a sharpie along the damaged plugs' insulator that is in line with the ground strap. Re-install it and note the lines' orientation with something adjacent on the engine. Remove. Mark a bunc of other plugs with the same line and install/remove them in the suspected cylinder until you find one that lines up like the damaged plug did. Install the rest of the plugs and fire the engine.

Internal engine parts don't magically tighten up again so if it's some loose parts flopping around the new indexed plug will get hit.

Dan

Dont think this engine needs to be indexed. If it was a index problem it would of damaged the offening plug when it was 1st fired up.. Its got to be forigen material suckud up or a chunk of carbon, piston, ring valve. Compression test should tell I would even do a leak down test also. It is possible to loos a small piece of the piston edge above the ring and not really have low compression. I would atleast pull the plug, turn it over until the piston is full down and look in there with a fiber light and see if all looks well.

ss3964spd
05-18-2010, 12:47 PM
Dont think this engine needs to be indexed.
I'm inclined to agree, was just suggesting this as a quick troubleshooting exercise.

Moot, however, if the plugs are located dead center in the top of the head. Would be interesting to know what the design of the c-head chamber looks like, as well as the top of the piston.

Hawkeye
05-18-2010, 01:15 PM
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

When exactly did the shaking and noise start? What year,mfg and modle engine are we talking about? DF250 suzuki?

EricF
05-18-2010, 01:28 PM
Sounds for all the world like foreign object damage. Something ran through and did a little bit of damage and moved right along. Inspection with a bore scope or flashlight on the piston head at TDC will show small dimples on the piston most likely, from it bouncing around in there. Sounds like whatever it is has gone along its merry way, just be nice peace of mind to verify some foreign object damage exists on the piston top before dismissing the issue as simply that. Any dimpling or such on the piston should not affect anything in the future...

nautiduck
05-18-2010, 03:17 PM
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.

Do you still have the plug? Check the center electrode and check it for size. Rarely when you have an impact does the tip just get bent over barely touching the electrode. Usually with an impact its mushed down pretty good with a broken center. If you still have it push the center in see if it moves away from the tip. If so you know it was just the plug. Also when you run the engine again, pull the wire off of that plug and see if the noise comes back.

One other thing, you said you noticed the vibration on the previous trip. That wasnt your first trip of the season was it?

ScarabChris
05-18-2010, 04:36 PM
There is/was a foreign body in the cylinder at one time....could be a piece of piston, something sucked up the intake, best to pull the plug and check it with a bore scope....do it soon...

I agree, something hit that plug. I would be amazed that a piece of carbon pressed in that electrode.



same thing happen to me also.changed the plug out and ran it. kaboom!
this was a 225 evinrude.don't run it pull the head and take a peek.

Yeah, I had the same thing happen to an old 150 Johnson. If you have no access to a bore scope just pull the head. It shouldn't take more than 30 minutes and 40 bucks for a new head gasket to be absolutely sure.

I took the chance, it wasn't good.

It would suck to be running 5000 RPMs on a beautiful fishing day and BAM! Ask me what that feeling is like.

PelagicHunter
05-19-2010, 06:04 AM
UPDATE:

did compression on all the cyliners and everything checked out ok, looked inside to see the piston w/ a bore scope and everything looks fine beside a little carbon buildup. took the boat out and pushed it hard and everything ran fine. came back and pulled that plug and it looks great. whatever it was that caused that, be it user error insertion, or something hit it, or whatever it was, its gone.

compression and visual insepection revealed nothing.

the mystery remains.

mobjack22
05-19-2010, 08:50 AM
Don't question it anymore, bad mojo. ;cool;

Glad it worked out for you.

HighSpeedPursuit
05-19-2010, 09:20 AM
Do you know what the compression was and what it is supposed to be for these motors? Glad that it appears fine, run them hard.:thumbsup:

UPDATE:

did compression on all the cyliners and everything checked out ok, looked inside to see the piston w/ a bore scope and everything looks fine beside a little carbon buildup. took the boat out and pushed it hard and everything ran fine. came back and pulled that plug and it looks great. whatever it was that caused that, be it user error insertion, or something hit it, or whatever it was, its gone.

compression and visual insepection revealed nothing.

the mystery remains.

PelagicHunter
05-19-2010, 09:31 AM
Do you know what the compression was and what it is supposed to be for these motors? Glad that it appears fine, run them hard.:thumbsup:

yes i got the numbers out of the manual. its a range something like 156 to 212, but more importantlly its not supposed to be more than 14 psi between the cyliners. it was all within range.

Hawkeye
05-19-2010, 09:35 AM
UPDATE:

did compression on all the cyliners and everything checked out ok, looked inside to see the piston w/ a bore scope and everything looks fine beside a little carbon buildup. took the boat out and pushed it hard and everything ran fine. came back and pulled that plug and it looks great. whatever it was that caused that, be it user error insertion, or something hit it, or whatever it was, its gone.

compression and visual insepection revealed nothing.

the mystery remains.

the motor was running fine, i changed out the water pump and put the motor on a hose, it peed fine, but it was vibrating ( i had noticed vibrating from the last trip) so i heard this rattling noise, checked the lower unit, everything fine, pulled the plugs, one had been bent. changed the plug, then motor ran fine



When did this vibration start? You say last trip but when and what speed were you running when the vibration appeared?

slickster
05-19-2010, 11:45 AM
If the piston contacted the plug tip, it would DESTROY the plug and continue to worsen until BOOM.....was the top of the piston smooth or have small pock marks in it like something was rattling around in there?....hope all comes out well.....

Grady Wahoo
05-19-2010, 01:05 PM
Did anyone besides you winterize/work on that motor? I was spraying some lubricant into my big block cylinders once and the red plastic straw fell off the can and disapeared inside the spark plug hole. I think I had a thread on another forum asking what would happen to that little straw...

PelagicHunter
05-19-2010, 03:53 PM
Did anyone besides you winterize/work on that motor? I was spraying some lubricant into my big block cylinders once and the red plastic straw fell off the can and disapeared inside the spark plug hole. I think I had a thread on another forum asking what would happen to that little straw...

Only I work on my motors and I'm pretty careful to not bang or hit the plug bf I screw it in, so I'm not saying it couldn't have been user error, it couldve been me but I doubt it...in response to when the vibrtion started, it started last trip out, no crazy running, just at 4000 to 4800 rpm and I noticed the mtor was vibrating, but nothing crazy, it still had power, ran fine, but it was recently when I had it on muffs did I notice the sound and vibration and I pulled the plugs and found it. Once I replace the plug all was well, visual inspection of the piston revealed nothing. Compression check was fine. So i really don't know what it couldve been. I'm gonna decarb the motors , I have 800 trouble free hours on these motors and I think it's time to decarb

surly
05-19-2010, 04:40 PM
delete

prober
05-19-2010, 05:01 PM
Glad it's OK. It coulda been carbon. Like I said I had a chunk break off and bend a valve in a small block chevy. Sounded like it was going to throw a rod. Dissolved the carbon and it was fine after that.

CONCHY CRACKER
05-19-2010, 05:39 PM
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,,,

There's an easier way to check.
Take the plug out. Hold a flashlight looking into the plug hole. Have a friend turn the fly wheel with a adjustable wrench on the crank shaft nut until the piston comes all the way up to the top.
Then turn it a little more so the piston is on the way back down.(just a little) Take a philips screw driver and just make contact with the piston. Here's the important part pay close attention when you do this. Push the screw driver with a little force. Is there any movement ? If there is you have a bad rod bearing or the wrist pin and piston connection has a problem.
If no movement under pressure confirm by turning the crank shaft to make sure the piston wasn't at the bottom of the stroke or on it's way back up.

conehead39
05-24-2010, 06:42 PM
Compare the ground electrode (the adjustable tang) with the other plugs.
Is it bent down into center electrode or
Is straight across like the other and the center electrode is down touching the ground electrode.

Don't throw it away .Take a side view photo and lets see it.

DogTired
05-24-2010, 07:19 PM
Rod bearing or more than likely piston bearings on that one cyl. What does the top of the piston look like where that plug came from? You should be able to see that looking into the spark plug hole if you turn that piston over to where it is at the top of the Cylinder. Might be just a tiney nick right in the center of the piston lined up with the plug hole. Rod or piston needle bearing failures are very rare and often very subtle and not detected. Normally observed as a slight audible knock or rattle sound..usually at idle and not often at high RPM.

Good luck, if something closed your plug gap on it's own then you are on borrowed time. If its a piston bearing then you are due to scuff a piston skirt on the cyl wall..if you havent already...meaning a rebore of that Cyl wall at a minimum.

If its a crank bearing then you have probably already ruined the crank journal.

One's not any worse than the other except if you did not scuff a cyl wall. Better to work the crank if not too bad than have to bore the bad cyl in the block.

Probably $325 for one hole, piston and bearing plus block labor which might be $800 to investiagate and get a seal kit.

Or you could just run it for a while and buy a whole powerhead and get it installed for around a few grand.

You should be glad you caught this..most would not.

Mr. Demeanor
05-24-2010, 09:11 PM
Its over, motors fine, nothing to see here....move along...move along....

PelagicHunter
06-19-2011, 07:48 PM
UPDATE: 6/20/2011

after this post was originally started 5/2010 and 400 hours later....i lost the cylindler...looks like the piston/ rod / block finally gave out.....all the other spark plugs look fine..this spark plug which was pushed in on the tip a year ago finally got completely destroyed and that cylinder gave out.....


now its time for a rebuild/ powerhead....the motor ran completely fine for a year and 400 hours.....something caused it to go...

Mr. Demeanor
06-19-2011, 08:12 PM
Thats was a good 400 hours!

Maineiac7x
06-19-2011, 08:52 PM
That was a lucky 400 hours

Mr. Demeanor
06-19-2011, 08:54 PM
Theres a big part of me that has a hard time thinking something mechanical could have been bad enough to close a plug gap and the engine still ran another 400 hours. Who knows though....

prober
06-19-2011, 09:11 PM
The damage could have been done by carbon as mentioned and slowly tore itself apart after that. It could also have been detonation which can cause not only the spark plug to be pushed in but also puts way more pressure on the crankshaft and bearings, wrist pins etc. It would only take a few minutes of detonation to cause enough damage to one of those parts to increase the clearances and then it slowly beats itself to death.

Detonation from poor fuel or poorly tuned engines creates much higher cylinder pressures than the engine was designed for. If you hear rattleing you should shut down and figure out what the cause is or you risk destruction of the engine.

PelagicHunter
06-20-2011, 02:38 AM
never heard any rattling. we would run the motors for a 300 mile trip routinely....there was no sign that there were any problems w/ the motors except that closed gap on the plug from that one cylinder.

gonna be in touch w/ the dealer today to see how much im screwed for

ill post pics of that plug soon.

Tomg33
06-20-2011, 02:25 PM
Wouldn't hurt to do a compression test.Peek into the cyl with a camera. Look for any filings in the exhaust.

puppy
06-20-2011, 02:56 PM
thankyou for posting this update.

PelagicHunter
06-27-2011, 01:16 PM
well heres a pic of that destroyed plug:

http://images2.snapfish.com/232323232%7Ffp539%3B5%3Enu%3D4%3B%3B8%3E475%3E256% 3EWSNRCG%3D337852%3A%3A4%3A347nu0mrj

southardlee
07-20-2014, 10:12 AM
I have a twin engine boat and it has happened on both engines. The mechanic said poor fuel ??? Mine is just closed not rough around the spark plug.



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