Cross threaded spark plug?

kwm · 07-17-2006, 08:36 AM

I really almost hate to ask this question for fear of the answer. How do you know if you have a cross threaded spark plug? My #5 plug when in much tighter than the others. I am now almost afraid to back it back out. I have plans to rebulit the engine this winter. I dont want to back it out and then not be able to get it back in. Second question, do I just leave it in till this winter or back it out? Thanks

scottb · 07-17-2006, 09:43 AM

I've never experienced this problem on my 911, but in the past I've had similar problem with other cars. It's usually just some gunk on the threads.

That having been said, however, you don't want to force it. Can you back it out a couple of threads, and then spray the threads with somehthing like PB Blaster? PB will wick down on to the threads that are still in the engine, and might loosen up whatever it is that's keeping the plug from coming out.

Good luck.

Hugh R · 07-17-2006, 09:50 AM

If its not leaking gas around the plug, I'd say leave it until you pull the engine and can get a straight shot at the hole with a spark thread chasing tool, NOT a plug tap, which will cut new threads. I did this to #2 on my car last year and pulled the engine and got a chasing tool and my brother the machinist cleaned it up nicely using heavy grease to lubricate and catch the filings. If you pull it out now, you'll have to deal with running it in again and its tough enough to put them in straight with the engine in the car.

kwm · 07-17-2006, 09:50 AM

I got the original plug out. As I went to put my plug back in it would thread in about a 1/4 to a 1/2 then get real hard to tighten. I ran it in and out about 12 times each time the threads had black gunk on them. Each time I woudl clean the plug and repray in with WD40 then I started to blindly of course spray WD-40 down into the spark plug socket. I got the plug in in but it went in real tight.

kwm · 07-17-2006, 09:55 AM

Thanks hugh I was starting to think I was the only guy ever to do this. I agree that getting plugs in and out of this car is very difficult. Can anyone who has had thier engine apart tell me if the plugs even go in straight? If I feel into the spark plug socket with my finger on plugs that are fully installed and touch the tip of the plug it feels like some of them are at a slight angle.

Gunter · Gunter's Garage

They are at a slight angle.
Usually, the carbon-build-up on the ends of the plugs leave some stuff behind when removing the old plugs.
New plugs should go in fairly easy (An extension on the plug-socket) threaded in BY HAND for the first threads to make sure the plug is aligned.
If it feels to tight with a ratchet, stop, back the plug out.
Use a thread chaser or:
Take an old plug and cut a v-shaped slot perpendicular to the threads with a ZIP-grinder, put grease on the threads to catch the gunk and start again. Back out and clean periodically.
Use grease, not WD40.
If in doubt on cross-threading, wait until the engine is out to deal with it.
I use anti-seize lube on the plugs even though Porsche doesn't recommend it.

Doug Steinel · Doug Steinel's Garage

If the car runs fine with the plug as it is, leave it alone and deal with it when the engine comes out. I would only mess with it if the car seemed to miss on that cylinder.

Jim Garfield · 07-17-2006, 03:19 PM

The same thing recently happened to me. As someone mentioned, the thread chaser is what you want with lots of anti-sieze. Go easy 5 or 6 times and clean off the threads each time that you take it out. Good luck.

Can't get #4 plug in.