My son has a 2000 GT, 4.6L, 5 speed, that is having some issues with spark plugs. The plugs are backing out of the driver's side head, we thought that we had it fixed the first time that it happened, however, it just happened to the plug behind the one that we had fixed. It's not using oil, only misses on the cylinder that is loosing the spark plug. He tried using a heli-coil to repair the damaged threads, now something is hitting the bottom of the spark plug and messing up the gap on just that one cylinder. Any ideas?

 

Yeah, the helicoil was installed too deep and the piston is hitting the plug.
Keep running it like this and you may shatter the piston, destroying the whole engine.
There is a special thread repair set for the modularfamily ofengines.
These engines are notorious for blowing out spark plugs.
Whoever helicoiled your spark plug hole may have ruined the cylinder head.

You should be posting this in the 4.6 modular forum.

 

This is posted in the 4.6 forums? Maybe a moderator moved it????

By installing a heli-coil a few thousandths of an inch too low which allows the plug to touch the cylinder won't "shatter" the piston. That's ridiculous. The spark plug will merely bend inwards and break the electrode off and divit the top of the piston. Now if the heli-coil was way to long or pressed in way to far(.020"+ below specs), then you have a severe problem. Well, you will have a severe problem with your valvetrain if a plug breaks inside there!
I haven't come across one modular head that has been repaird with a helicoil that would perform as good as a stock head. The tolerances are just un-imagineably close for proper combustion.

 

from what I have read on here, a lot of people say the timesert is a superiorrepairfor stripped threads than a helicoil. might want to look into that.

 

I wouldnt recommend running the motor anymore, until the problem is fixed. Sounds like your gonna need a new head! Any repairs done to that existing problem will not hold up in the long run.

 

I blew out a plug, put it back in, pulled it out, ruined the threads and then ran a helicoil into my car *basically this is a short recap of the events leading up to your quote, just in a different order for myself.

The helicoil was fine for somewhere between 1500-2K miles.

It developed a miss, and then after doing a burnout one day it ran like **** that night. Took the same plug out that I had helicoiled and it was bent in, exactly as your have described in your post.

So I drove the car, on 7 cylinders, to the shop where I was having my tires installed and they diagnosed a bent valve.

Now, I'm not sure how all of these things are related, as in I don't think the piston is coming up hitting the plug, and likewise the piston coming up into the valve, but something is up.

I suggest a new head. Tiresome, but worth it.

 

I had this happen to me a few months back, Did you buy new plugs or is the spark plug your using have full threads?Some plugs have threads that go all the way up the thread part of the plug and some only go half way. So if you have the plugs with full threads, you might be able to use the half thread plug(autolite 764)

 

I don't know if that suggestion was to me or not, but if so, I'll go ahead and reply.

The car would'nt take any plug at all, a new one, or the same one. The threads must have been so chewed up, and I doubt it would have mattered anyways, if there were only half threads holding it at the time, they woudl have just blown out when the plug came out again, which I'm certain would have happened.

After the plug got bent in and the alledged bent valve happened, I tried putting a plug *correctly gapped* in once more with the helicoil, but it would'nt go either.

So I now don't know if the helicoil's damaged as well, or what. Not that it matters, I'm getting a new head anyways with cam/valve train and such loaded so that I hopefully won't have to deal with any more blown plugs.

As for trying something now, car's torn apart.

 

No sorry i just used the quick reply. But i had a plug blow out and had a shop put a helicoil in and they put in too far,or something. i bought some bosch plugs that had threads all the up andthe plug with the helicoil got bent, so i went and bought the autolite 764 where the threads are only half way up the plug, and it runs good now.

Dont know if that makessense, but i don't know how to explain the threads ondifferent plugs