So I blew a plug out of the head today...

[poor_red_neck]

Don't know wtf happened.

I was driving down a 55mph highway... guy in front turned off, so I got down into 3rd gear, WOT, and was going to shift at about 5000/5500 or so. When it got to about 5000 I heard a pop and lost power. Sounded like the exhaust got knocked off or something. So I pull over and find my spark plug, still attached to the wire, chilling in the engine bay. The threads on the plug are fine. The threads on the head (or lack thereof) were smooth as a baby's bottom.

I have not removed that plug since I've owned the car. About 3 months.

I've drove the dog shit out of this car since I've owned it, redline it from time to time, but never over-revved.

I just recently removed all the emissions, so I'm quite sure it wasn't detonation or pre-ignition. I have not messed with the timing at all either. It's the same since I've owned the car.

I went to advance auto and they didn't have a helicoil that would fit a spark plug, so I got one of the "spark plug thread repair kits."

Basically the same concept. It came with a tap, tapped the new thread. Now I know you're supposed to remove the head to do this, but we greased up the tap pretty well to catch as many of the shavings as we could. Shop vacced the cylinder out as best as we could and cranked it over with the plug still out to hopefully shoot any small remaining pieces of aluminum left from tapping the new threads.

What the hell could have caused this? I mean, it could have been mis-threaded when that plug was put in the car, but I guess the question is why did it just go all of a sudden? Who knows...

Got the new plug put in and cranked it. Was still acting funny. I thought "ah shit" it must have detonated and blew a valve or the rings out too. After running for about 2 minutes it just poof went back to normal.

Now I'm afraid to even give it 20 percent throttle or go past 3K rpms.

You think now that it has new larger threads cut in it it'll be "just as good" as before?

This is the product that I used... not this brand but the exact same thing. Came with 3 different sized inserts and a hammer tool. Once you get the insert threaded in you smack it with a hammer and this special tool to lock it in there.

[jdaddy88lx-i]

I havent heard of that on before.

[AccordB20A]

at least theres a way to fix these as the stupid a20a engines allways strip threads

[russiankid]

What i think happened was the plug was cross threaded and installed incorrectly.

[poor_red_neck]

That's the only thing I can guess happened.
Just a fluke that it happened tonight.

Think the thread repair is OK?

[russiankid]

That's the only thing I can guess happened.
Just a fluke that it happened tonight.

Think the thread repair is OK?

Time will tell.

[SZfiftyfour]

even crossthreaded the plug wouldn't just pop out. if anything it'd be harder to get out. if the thread wall was smooth it sound like maybe someone before you had already drilled it out and used one of those thread inserts and it broke free. make sure its seated well.

[poor_red_neck]

Yeah, i mean if for some reason there was extra pressure inside the cylinder for whatever reason, I would think I would have had a rod bend, rings fail, or valve fail or something before it would just shoot a spark plug out of the cylinder and not show any other damage.

[AccordB20A]

What i think happened was the plug was cross threaded and installed incorrectly.

bingo, all the a20 engines ive had have all had at least 1 of the sparkplug holes stripped by people before me. if u ask my they didnt think about the head layout too well as its hard to get them in square when installing a new plug. I dont think there was any extra pressure in the head to make it do that.

[2drSE-i]

you will know immediately if something else is wrong man. a bent rod sounds AWEFUL, knocks LOUD. a bent valve sounds pretty damn bad too. i just think it was cross threaded. It popped violently because there is no soft way for it to come out.

[russiankid]

bingo, all the a20 engines ive had have all had at least 1 of the sparkplug holes stripped by people before me. if u ask my they didnt think about the head layout too well as its hard to get them in square when installing a new plug. I dont think there was any extra pressure in the head to make it do that.

It is not that bad, just take your time. To my knowledge the BMW engine is a total bitch. When my brother had to change the spark plugs, the plugs that are closer to the fire wall are totally out of sight. You need a mirror to see the hole.

[w261w261]

Mac Tools makes a rethreader kit that works from the inside out, which eliminates the threat of dropping cuttings down into the cylinder. If I were going to rethread a spark plug hole, this is what I'd use. See the "featured product" here:

http://mactools.com/Mac/

[race12001]

yea i had it happen to mine after iput my cam in and i still give it hell and hadnt had a problem yet

[lostforawhile]

you did the right thing by greasing the tap first,i'm sure it will be fine,did it cut new threads then you screwed in the insert? if so it's probably just fine. it sounds to me like it had a problem before,i've even heard of people hammering in plugs when the thread was screwed up. one thing to do when you change plugs for the future, get a spark plug thread chaser,it looks like a tap,but it just cleans out the old threads, they build up a lot of carbon and junk in the threads,and when you try to screw in the new plugs,it's hard to do,so a lot of people try to screw them in with a wrench. this is often how they get cross threaded. if you can't start the plug with your fingers,then you need to clean out the threads. you should be able to screw it in by hand a number of turns with no problem, this makes sure it isn't cross threaded.

[AccordEpicenter]

I hate aluminum threads, they get fuct up really easily, just soo soft

[lostforawhile]

I hate aluminum threads, they get fuct up really easily, just soo soft

yea if i was rebuilding a head i would install helicoils on the plugs as a matter of security. then you havve strong stainless steel threads instead of soft aluminum threads.

[AccordEpicenter]

agreed 100%