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Old 07-12-2012, 10:14 AM   #1
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Piston hits plug

Hey guys,
I was wandering what would cause a piston to hit a plug? My car had a set of E3 plugs put in it about 3 thousand miles ago and has ran perfectly. I checked the other plugs and they all look good. The piston moves smoothly in the cylinder and the piston looks good except a small place where the piston hit the plug. It hit hard enough that it blew the plug out of the head with all the threads. It is obvious that the piston hit the plug I'm just trying to figure out why it happened to just one cylinder. Any Ideas?


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Old 07-12-2012, 10:30 AM   #2
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I've read where some 4.6's blow plugs/threads out.. Not sure if piston interference was involved or not..

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Old 07-12-2012, 11:06 AM   #3
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Unfortunately it is common with our engines to blow plugs. Some years only have 3 threads for the plug to screw into. Get a heli coil kit and you should be fine.
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Old 07-12-2012, 12:32 PM   #4
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Re: Piston hits plug

I agree with guys above, it blew the plug out without the piston hitting and the plug hit something as it landed or as it was coming out to making the ends smashed in like the piston did it. you can shine a flash like down in the spark plug hole with that piston close to TDC and see if you see any marks where the plug hit, if you want to see if it did.
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Old 07-12-2012, 12:43 PM   #5
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Yea there is a knick in the piston where it hit it.
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Old 07-12-2012, 12:44 PM   #6
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Bad timing
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Old 07-12-2012, 12:50 PM   #7
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Re: Piston hits plug

Quote:
Originally Posted by Bret21 View Post
Yea there is a knick in the piston where it hit it.
Hmm, I would ask if you got the right plug but they been in there for 3K miles thats weird. I hope nothing is coming loose or going bad on that one piston causing it to come up too far....

Maybe try a different plug and see if it does it again....

---------- Post added at 12:50 PM ---------- Previous post was at 12:48 PM ----------

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Originally Posted by GrabberBlue5.0 View Post
Bad timing
If it was that you would think it hit a valve first wouldn't it?
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Old 07-12-2012, 12:51 PM   #8
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I had this happen to me in in.my old 91 gt it only happened when i was a WOT we could never figure out what caused it but i would be careful when i tore my motor down it had cracked the piston almost in half
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Old 07-12-2012, 01:58 PM   #9
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It just done it while I was cruising at about 50 mph. I thought it was kinda weird too. If its messed up the pistons and stuff I'm just gonna go ahead and put some forged internals in it.
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Old 07-12-2012, 02:03 PM   #10
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Re: Piston hits plug

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It just done it while I was cruising at about 50 mph. I thought it was kinda weird too. If its messed up the pistons and stuff I'm just gonna go ahead and put some forged internals in it.
def a good idea thats what I did
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Old 07-12-2012, 03:27 PM   #11
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Quote:
Originally Posted by southernstang00

Hmm, I would ask if you got the right plug but they been in there for 3K miles thats weird. I hope nothing is coming loose or going bad on that one piston causing it to come up too far....

Maybe try a different plug and see if it does it again....

---------- Post added at 12:50 PM ---------- Previous post was at 12:48 PM ----------



If it was that you would think it hit a valve first wouldn't it?
Ha, crap you're absolutely right, I don't know how i mixed up valve with spark plug lol
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Old 07-12-2012, 03:35 PM   #12
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Re: Piston hits plug

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Ha, crap you're absolutely right, I don't know how i mixed up valve with spark plug lol
See im good for something lol ....But it sounds like to me the piston came above TDC and thats why it hit....So the questions

What would cause a piston to go above TDC? bad bearing? bearing shifting? too play somewhere in the rod and piston?

We know he has the right spark plug or he would have know it right off the bat and not 3k miles down the road. I say do the repair like said above and if it does it again then ya might want to tear the engine down.

I'm intrested to see what it is.
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Old 07-12-2012, 04:07 PM   #13
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If a rod was coming loose you would have a knock. Bad bearing would cause a drop in oil psi and weird noises from the bottom end. Sounds funny to me that the piston slapped a plug that's been in the engine for 3k miles with no issues..... Might want to do that rebuild now before something bad happens and you end up having to buy a engine.
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Old 07-12-2012, 04:17 PM   #14
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Do Rods stretch?
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Old 07-12-2012, 06:40 PM   #15
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Wrist pin maybe? Any tapping noises?

Maybe the threads collapse inward first, and the piston is what has been blowing them out..?

Who knows..
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Old 07-12-2012, 07:04 PM   #16
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No tapping or anything. It's kinda got me stumped lol
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Old 07-13-2012, 12:47 AM   #17
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Re: Piston hits plug

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Originally Posted by 95v686gt View Post
If a rod was coming loose you would have a knock. Bad bearing would cause a drop in oil psi and weird noises from the bottom end. Sounds funny to me that the piston slapped a plug that's been in the engine for 3k miles with no issues..... Might want to do that rebuild now before something bad happens and you end up having to buy a engine.
Thanks for the info....

---------- Post added at 12:47 AM ---------- Previous post was at 12:42 AM ----------

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No tapping or anything. It's kinda got me stumped lol
You might be able to go to a Ford Dealer or speed shop thats well known and ask for a master tech to ask him what caused it to do this and explain to him everything you posted in here. I've done it before and got my answer to the what I was looking for.
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Old 07-13-2012, 02:09 AM   #18
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Did it ruin the coil pack? Had the same problem 03 gt she spit out a ngk did some research and turns out supposedly motorcraft (OEM) are literaly a hair different the most brands although all your other plugs didn't blow this could be your problem be safe and get you motorcraft and get a helicoil in there and you would be good to go it only takes one the start the domino affect I got my cylinder 7 changed out and heli coiled and didn't Change the others and within another 2weeks number six blew
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Old 07-13-2012, 02:20 AM   #19
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Quote:
Originally Posted by southernstang00

Hmm, I would ask if you got the right plug but they been in there for 3K miles thats weird. I hope nothing is coming loose or going bad on that one piston causing it to come up too far....

Maybe try a different plug and see if it does it again....

---------- Post added at 12:50 PM ---------- Previous post was at 12:48 PM ----------



If it was that you would think it hit a valve first wouldn't it?
Depend on the cycle of the motor the valve could ave gone back in just in time for the plug to slip out the valves have to be close in order for the post to go all the way up here are some pics from whe I did a head job on my 03 gt about 2 months ago 1st pic is the under side of my head with no rockers in it witch would mean all the valves would be closed and the 2nd pic you can see cylinder 7 (3rd one back) is all the up meaning the valve would be closed
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Old 07-13-2012, 04:41 AM   #20
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Re: Piston hits plug

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Originally Posted by trejo_03 View Post
Did it ruin the coil pack? Had the same problem 03 gt she spit out a ngk did some research and turns out supposedly motorcraft (OEM) are literaly a hair different the most brands although all your other plugs didn't blow this could be your problem be safe and get you motorcraft and get a helicoil in there and you would be good to go it only takes one the start the domino affect I got my cylinder 7 changed out and heli coiled and didn't Change the others and within another 2weeks number six blew
Thats why I only run motorcraft plugs but thats my preference but i def agree. Thats for the info above as well and you make a good point, good pics as well.
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Old 07-13-2012, 05:27 AM   #21
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I'm kinda in the same boat this week!
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Old 07-13-2012, 03:34 PM   #22
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Yea it blew the coil pack off and everything. I'm prolly just gonna go ahead and put some forged internals in bc I just bought a kenne bell.
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Old 07-13-2012, 04:03 PM   #23
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Defenantly the way to go just get some.New heads
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