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Hey all , after starting to change the plugs today i found that some muppet had partially stripped one of the threads.

As i took it to the local main dealer for a complete major service and cam belt change not long after i got it , to say i'm not impressed would be an understatement ,they either didn't do the plugs or " forgot " to mention it to me, but i can't prove it was them.

It seems to be mullured from top to about 1/4 of the way down.

My question is, will this make a difference as i'm not sure if the new plug is totally in as far as it should go as the amount of pressure i was putting on the wrench made me think to stop before something went snap !!!.

My thinking is that if the tip of the electrode is not as close as it should be, will this harm the engine when that cylinder fires ??.

I started her up and eveything seems ok but thought i would seek some advice from the more mechanically minded among you.

The head can be salvaged by helicoiling (tapping it to a larger thread size and then putting an insert ib to bring it back down to the correct plug size) unfortunately this is a head off job so not cheap.

If you've only lost a 1/4 of the thread length then you might get away with it, it depends on the state of the rest of the thread. The other worry is if any of the bits of stripped thread fell into the piston/bore area.

If the plug doesn't screw in fully then it doesn't seal properly and you will be loosing compression on that cylinder because it will leak up the threads.

Hopefuly I'm not teaching my Grandma how to suck eggs here.....

Fog

the only real risk is the possibility of a burnt valve as the combustion will take place closer to the cylinder head, i wouldnt use a a helicoil on a plug head, you will still loose compression through it, you either need to be very hand with a tap and die or find a good machine shop to put in a wúrth timesert, it wont be easy on a turbo, but just be glad its not a 16v as repairing it would be next to impossible

Foghorn Leghorn wrote: The other worry is if any of the bits of stripped thread fell into the piston/bore area.

Fog

That's what i'm worried about.

Burnt valves eh James, hmm that doesn't sound good - how would i know if this starts to occur ?, will there be a loss in power or a knocking noise or something ?, and if left will it become terminal ?.

well the first sign of a burnt valve is a permenant misfire at idle and a distinct loss of power, you wont get any noise warning you of it, it may just suddenly occur, high intake temps' wont help, i.e. hard acceleration and high revs arround town at low speed with the a/c
depending on how far the plug is in the head, its hard to say how long it will last, but as you dont seem to be loosing any power indicating a loss of compression then i wouldnt touch it, as removing it will do more harm than good unless you plan, as i said above, taking it to a machine shop to have a wurth timesert fitted

Ok matey, cheers for that, i'll leave it alone and hope for the best

Sounds familiar :/ 2 of my plugs have buggered threads so they're hanging worryingly far out. Thankfully it's been a while since I changed them and I've not noticed any ill effects yet.