Blown out spark plug

[ouch1011]

A few days ago, I had a 98 OB towed into the shop I work at. Concern was that they'd driven about 300mi or so from N. Washington down to Oregon where I live, stopped somewhere, and when they restarted the engine, they found it was very noisy. Turned it off, had it towed to the shop. I inspected it, found the rear spark plug on the right bank had blown out of the head, stripping the threads. Took the head off, sent it out to the machine shop to have a thread insert installed, as well as have the head inspected. Should be getting it back tomorrow. Sounds like a nice way to spend your vacation, eh?

Anyway, I know very little about the history of this car, since they are from out of town (not regular customers). But it appears to have been decently maintained and had a recent tune-up. I'm reasonably certain that this mishap is a result of some improper work from the previous shop who did the tune up (spark plug too tight or too loose, stripped the threads while removing the old plug, etc), but I was curious to know if anyone else has had this problem.

Btw, if that OB belongs to anyone on here (doubtful, but maybe) sorry your car left you stranded. But hey, at least I've done this job before! lol

[ouch1011]

Guess not...

Anyway, got the head plopped back on with a new gasket, cam seals, timing belt and tension and sent them on their way back to WA.

[DN1911]

i actually just had this happen two days ago on my 95' LSi. i haven't had the car but for a couple of months and had a huge service history through the Subaru dealer where i work. after trying to put the plug back in, i realized the threads were FUBAR. just pulled the head last night and it is going to the machine shop tomorrow.

our head mechanic has seen plugs back out before. some can be tightened back up some can't. just have to check them once and a while on the aluminum heads

[ouch1011]

Yeah I've definately seen plugs back out before and I kind of suspect that might be what happened in this instance, either that or the plug was overtightened and stripped. Gasketed plugs like our engines have (or at least the DOHC, I'm assuming the SOHC is the same) don't usually back out or need retorquing if they are properly torqued the first time because the gasket crushes and kind of preloads the plug so that it doesn't loosen up.

[d1giPhux]

Damn.. how much all that cost em? Least they found somewhere good to break down i suppose. LOL.

[ouch1011]

I believe it was about $1000. It's nearly the same amount of work to do 1 head gasket as it is to do both, since you still have to remove the exhaust, timing belt and unbolt the intake manifold. The only additional labor is to remove the other cam cover, cams and head bolts, which is only probably another 1 or 1.5 hrs. The cost from the machine shop was minimal, it doesn't take much for them to install a thread insert.