Technical Spark plug cross threaded what next?

[DaveMcT]

When you buy an old(er) car its either no worries for ages or immediate hassle. Guess what always happens to me. :-(

If its already been down the worst that can happen is the coil will unscrew. But if it has been coiled its actually less likely to cross thread because the coils are made of steel.

You can try carefully moving it back and forth with ever more anti clockwise until it comes out. BUT you then have a hole with no thread and the car NOT at the engineers who can fit a new thread. You cant drive it with a spark plug missing - explosive fuel/air mixture will be pumping out !!!

If you get too eager and snap the plug (VERY EASY TO DO), it will need engineering attention so its really best left to the pros.

The only snapped off spark plug I have seen successfully removed without stripping the engine was on an air cooled 900cc bike. A thin nut was welded onto the snapped off plug and managed to get it out. But thats almost impossible on a Fiat with deep plug pockets.

 

[dumbledore]

New old car I want to enjoy it first. When I get bored I do the spark plug if it brakes i won't mind a couple of weeks of no drive until I source another head.

 

[dumbledore]

Had another go on my top engine oil leak yesterday and when putting things together I tried to remove the plug. Guess what it came out relatively easy this time. I had a look and it does not seem to have a helicoil in there. However I believe the thread may actually be a bit weak. Is possible the previous owner has put some source of threadlock compound to stop the spark coming out. Anyhow I put a new plug in. It went in OK no cross threading. However, I suspicious about the condition of the thread I have not applied the usual final harder torque to it in case whatever thread is left is not completely damaged. So I will have to keep an eye on it to see if the spark comes out slowly by itself. If not I should be lucky.

 

[DaveMcT]

Dont allow it to rattle as that will strip the thread in very short time. A good mechanic should be able to helicoil or fit an insert without taking the head off.

 

[dumbledore]

Dont allow it to rattle as that will strip the thread in very short time. A good mechanic should be able to helicoil or fit an insert without taking the head off.

Have no good experience with good mechanic. Last time I gave the guy the full cylinder head. He put in an insert. Put in a spark plug OK, however after a couple of days I wanted to take the spark plug the whole spark plug and the insert come out. I had to put the insert back in with some quick metal paste. Let it set and then remove the spark plug which worked fine. I put a new spark plug in and hoped for the best. It still works and has not exploded out and is almost 2 years passed. Not contemplating removing that spark plug anytime soon though as is working hust fine (about 5K miles on them)

 

[DaveMcT]

Thread inserts (or sleeves) are better than helicoils. The latter only stay put by being springy. The inserts are Loctited with the permanent stuff.

They can unscrew, but once they are settled/loctited etc, helicoils usually stay put.

Its really a machine shop job but a good one should be able to do the job in the car. Grease on the tap helps to catch any metal bits and a vac with a small tube can make sure the cylinder is totally clean.