Hey fellas, I've been snooping around on here for a couple years now and now I need some help. My 98 3.4l has 225,000 on it and during a tune up last year I replaced all my plugs with Bosch, which turned out to be a huge mistake. Over a few months three plugs came loose (yes they were tight) and one of them actually rattled all the way out, stripping the threads in the head in the process. So I used a helicoil to fix the threads but then after firing it up, it ran like crap. As far as I can tell, when the plug was on its way out, the flame of the combustion chamber burnt off the electrode ground on the spark plug and it dropped into my cylinder. On its way out to the exhaust, it must have hit just right and bent the exhaust valve. Now I have a dead cylinder, it smokes, smells like crap, and runs horrible.
So my question is this: do I just do a valve job and top end rebuild or wouldnt it just be worth it to do a full rebuild? Obviously the cost will be a bid difference, but would a new top end put more strain on an old bottom end? I appreciate any input.

on my 96 had 220K ish miles when i got the exhaust leak fixed. in order to get to the flex pipe i had to remove the driver side head. while i was off i had a valve job done on it. not it has right around 270K miles and runs great! if you have enough power before the problem i would say just do the heads. these engines dont wear very much so i would ssay just do the heads and dont worry about it!!!

+1 on the heads, unless you can find a low mileage engine locally. Make sure to inspect it thoroughly and take off the VCs if you do:
Car-Part.com--Used Auto Parts Market

A prime example of why folks should never use Bosch plugs in 3rd gens, or Bosch anything except for wipers and batteries.

Good luck.

Thanks for the advice. Yeah I learned my lesson with Bosch. If it weren't for those stupid things I'd still be having fun and not having to do all this extra work. Going to stick with MGK for life now.
I've turned away from the idea of a used engine. Two reasons: a 150,000 mile engine is still over $1000, and I don't trust them. I think I'll do the head and see how far that gets me.
Anymore input is appreciated!

Yeah do the head. I have experience with my car (92 Toyota Sprinter = Geo Prizm!!!) with 225 K miles. Pistons and cylinder bores looks brand new with that many miles. I cleaned top of the pistons before I installed the rebuild head. It runs brand new with more pulling power and won't burn oil as it used to.

Toyota engine (pistons/bores) will last at least about 400 K miles. Just do the heads!

Evaluate it once the heads are off. If that electrode was laying in the cylinder, no telling what other damage it did.

I had the same thing happen, spit the plug on the way to work. Had the top end redone and runs great, new heads, valves water pump, timing belt..... ready for 250K more miles now!

Curious how much you spent for the top end rebuild?

Am thinking about doing mine, but unsure if I have the time to do it myself, so thinking with maybe just paying someone to do it.