S90RTRRO

at least the valves are in tact...as was the timing belt. I thought for sure it was a thrown rod or something by the horrible noises and clunking, back-firing and missing...but I kept thinking it sounded like a lawn mower with out a plug in it..(something my dad showed me way back to test if a plug was still good...that, and he thought it was funny to zap his 7 year old kid...hehe, but hey...i never forgot it), that, and it was strange that it still ran...
so I started tracing the plug wires, and sure enough...one is compromised looking, but then I grab that wire...and the entire plug comes right out with it. Crap. Well..that very minute, my new neighbor comes walking in to introduce himself. So, he introduces himself as mike, the missionary who works as a mechanic. I thought he was being funny or something given the circumstances...but he was dead serious. His fiancée and himself are going to the Congo or something when they get married. At any rate...halleluja I say. So he looks down in there and the threads are non existent. You guys think a bad plug that "detonated" or arc'd to metal would cause a plug to shoot out its threads? Am I looking at needing a new head, of do you think a re-thread kit would work? WWAW90D?

S90RTRRO

<img src="http://i191.photobucket.com/albums/z277/s90rtrro/babygirl244.jpg">
no question what it shorted out to....^^^

<img src="http://i191.photobucket.com/albums/z277/s90rtrro/babygirl250.jpg">
Ya..that wire is hosed....but whats wierd is that it wasn't the spark plug attached to the culprit wire that blew out of the head...it was the one directly below the point where it met the metal, which makes me wonder...would this cause a plug to blow right out of the threads of the head? I don't have a clue. I've never heard of a plug blowing right out of it's home. I tried taking pics of down in, but basically...it's smooth as a baby's butt where there should be threads...

iProDrive

overheating issue? this is most likely a first! sad story.

SCarGo02

Y'ouch. Makes ya wonder what caused that...at least it's not as sever as you though!

VAP

and had its threads completely or partially stripped. You couldn't come close to blowing a spark plug out of its threaded hole with 500psi of boost! Any internal cylinder explosion capable of blowing a spark plug out of good quality full-depth threads would've also easily blown the spark plug and boot completely out of the car, much like a 50 cal. bullet separating from its cartridge casing when the firing pin is struck. Hardly an explosion that would've left the spark plug/boot assembly nestling in the spark plug recess just sitting at the top of the hole. You'd have a nice big, behonkin' hole from the under-side of your hood above that spark plug and probably sever the fuel rail tubing if that happened and virtually guarantee a boot/wire separation as well and the spark plug wouldn't be within hundreds and hundreds of meters of the engine!! And gauging from the amount of blow-by on that spark plug boot this plug hasn't been fully seated/sealed in a very long time as that kind of crud cannot collect there in 10-20 minutes. I would suspect all kinds of under-torqued/over torqued spark plug values in this engine after seeing the results from just 2 spark plug scenarios from this engine.

Nothing weird, strange, odd or even rare about it. Happens alla time with aluminum heads.

Good news is it can be fixed via Heli-Coil or similar but heads gotta come off. And I'd be closely inspecting all 6 spark plug holes for evidence of the same thing. When one threaded bore has been compromised like this it's not much of a stretch to believe there will be more.

Luxus Panzer

I always tighten mine to 30 Nm (22 ft-lbs)

dtompsett

Little 1.8L VW engine... the low compression vw Fox engine. I hadn't touched the plugs in months and always torqued properly. Went out with a friend, stopped to get a sub, hopped back in the car, cranked *BANG*. Popped the hood, there's the plug and wire just sort of hanging. No dent on the hood.

Looks like the plug had loosened bit by bit... and finally blew out taking a few threads. You could get it back in and tighten it... but it wouldn't hold a torque and stripped the last remaining threads.

I ended up leaving the plug out and drove 35km home on 3 cylinders! It was a bit loud, and the car wouldn't hold an idle... was the coolest that engine has ever run! (only generating 3/4 of it's normal power, and that whole cylinder was acting like an air pump which cooled it down.)

Rebuilt a spare head, popped it on, and the car ran great afterwards.

of course, the car ran CIS... so the whole time I was driving on 3-cyl, that 4th cyl was being sprayed with fuel. I figured the latent heat and excessive air moving just kept evapourating it. I had a friend drive infront of me the whole way home... told her if I pulled over and started running, it was probably cause the engine bay had caught fire. hahaha.

VAP

however, the cylinder pressure required to blow out a few threads and the pressure required to blow out a "fully seated/threaded" spark plug are exponentially different. A few threads can easily be stripped/blown out at or less than 100psi while a fully engaged 14mm diameter spark plug with 20mm of thread depth engagement would require on the order of 3,000 psi or more cylinder pressure and would sound like a 50 cal going off and blow the spark plug thru the hood and hundreds and hundreds of yards away from the car.

I've got a couple spare heads out in the garage. Sometime this week I'll put one up on one of the "gauged" presses and see what kind of pressure it takes to blow a fully seated "torqued-to-spec" spark plug outta the head under pressure. The formula in the machinist's handbook works out to 3,062psi to strip a 14mm spark plug from it's fully engaged aluminum threads but I've got a sneaking suspicion it'll be closer to 4,500psi as 14mm is approx 45% smaller than the "inch" in psi.

90/90Qs

might have to add a heat source to get accurate results

rggpa2

...their plugs? Do you compress the washer, back off a bit and then torque the plug in, or just torque the plug and new washer first time? The reason I ask is I've only gotten an occasional "loose" plug when I do the latter; now I only do the former.