Difficulty fitting new spark plug

[AA77]

Changing the spark plugs on my Fiat 500 Lounge (2010). The old ones were quite rusty. Managed to get new plugs 2, 3 and 4 in (working left to right) but having trouble getting in plug 1. I am getting a lot of resistance after screwing in after about 12 quarter turns. The other plugs were fully in after about 45 quarter turns and only felt resistance for the last few turns. I am reluctant to keep trying to tighten plug 1 with a ratchet, although I assume at this point I could not have cross threaded.
Any suggestions? Could the thread I am screwing into just be rusty?
Thanks.

[Olivergt]

You should be able to do the first few turns by hand, doing it by hand removes the possibility of cross threading.

12 quarter turns is 3 full turns, that's probably about perfect to start feeling you have crossed threads.

Ang chance you can get a light in to the home and see what is going on?

But definitely don't use a ratchet till you have the plug in most of the way by hand.

[donkmeister]

Loosen the plug fully, then slowly turn anticlockwise whilst applying downward pressure until you feel it drop 1mm. Then start tightening by hand.

What this does is to ensure you have the male thread starting into the female thread at the correct point, avoiding possible cross threading.

[CorradoTDI]

Have you tried some oil / WD40 on the threads and checked the thread on the plug is clean?

Could also try one of the old ones back in to see how that feels

[AA77]

Many thanks for the replies.
When I removed this plug it was quite tight to undo intially and was also tight as I unscrewed.
I have tried re inserting some of the old plugs and other new ones but I get the same resistance after 10 or 12 quarter turns. These same new plugs screw in fine in the other 3 locations.
As the threads of the plugs look ok, presumably if any cross threading has occurred it is in the hole itself rather than the plug?
The location of the plugs on my Fiat 500 are so tight for space I can not actually put any of the plugs in by hand I have to put an extension socket on the plug and turn the socket extension gently by hand to get the plugs to start threading.
I will try a little WD 40 on the thread but think it unlikely it will make much difference as the plug feels so tight.
Thanks again.

[Boosted LS1]

Op, you could buy a 'plug chaser' to clean up the threads before you risk doing any damage.

[AA77]

Thanks, that sounds a good idea, didn't know there was such a tool, just found them on Eurocarparts so will go and pick one up later.

[TwinKam]

...and even more important than ever before to ENSURE that you are lined up 100% correctly when using this thread chaser, you have one chance at it!

[AA77]

Thanks, yes. In fact, I am going to go and see if my local garage will look at this for me. It will be an expensive mistake if I get it wrong!
I've tentatively tried a couple more times to insert the spark plug, but it is definitely getting stuck about half way in. Tried different plugs too, just to eliminate a problem with the plug itself. As mentioned before, when I removed the original plug it felt much tighter coming out than it should so I suspect someone has cross threaded it in the past.

Not sure if I can drive the car a couple of miles to the garage with one plug not fully in? It feels tight and secure but not sure if that is a very bad idea?

[richhead]

AA77 said:

Thanks, yes. In fact, I am going to go and see if my local garage will look at this for me. It will be an expensive mistake if I get it wrong!
I've tentatively tried a couple more times to insert the spark plug, but it is definitely getting stuck about half way in. Tried different plugs too, just to eliminate a problem with the plug itself. As mentioned before, when I removed the original plug it felt much tighter coming out than it should so I suspect someone has cross threaded it in the past.

Not sure if I can drive the car a couple of miles to the garage with one plug not fully in? It feels tight and secure but not sure if that is a very bad idea?

better to take the plug out and unplug the injector and drive there on 3 cylinders, rather than risk it blowing a half in plug out, it does sound like the head has been cross threaded, either this time or last time the plugs were changed.
Always start them by hand, even if using an extention, just take off the ratchet any finger tight.

[zedx19]

Driving with 1 plug not fully in will cause that plug to fly out the head, taking the threads with it, happened to me on a 172 I had many, many years ago. Not the end of the world though, thread was helicoiled and had no further problems, so don't get too wound up if you have cross threaded, there are solutions that don't involve replacing the head.

[AA77]

Thanks everyone for your help with this, very much appreciated.

Just been to my local garage, they referred me to a local company that repairs threads, unfortunately they can't get to me until end of the month.

Tempted to buy a thread chaser, but a bit put off as it sounds like I could make things worse if that doesn't work. I am fairly competent but the plugs are at the rear of the engine with very little access, particularly the one that is the problem, as it is right next to the dipstick too.

May just have to wait for the thread repair guy to be free.

[Panamax]

Boosted LS1 said:

Op, you could buy a 'plug chaser' to clean up the threads before you risk doing any damage.

Totally agree. This is definitely one of those "whatever you do, don't make it worse" situations.

[Bill]

If it was hard to remove, it's possible the old one was cross threaded.

[AA77]

Thanks Bill, that is my only consolation, it was probably cross-threaded by the last person to service it - that's what I am telling everyone anyway!

[Fastpedeller]

They probably used a windy gun the last time they replaced the plug I realise that's no help to you though - good luck!

[TwinKam]

For the future!
A spark plug runner should be in every tool box, for engines with recessed and or inaccessible plugs they make life so much easier, I simply never fit plugs without it. Until you've used one, you won't realise how helpful they are. Yes, I know you can use a length of hose to do the same job, but for under a fiver on the 'bay, you can get a double ended (not all plugs are the same) runner that has a straight memory, not a curved one!

[austina35]

I would advise against using a plug thread chaser whilst the cylinder head is on the car. You will put debris into the combustion chamber and that isn't what you want to do. All that metal splinters sliding up and down with the engine running. Only needs to find the edge of the piston.......

[Panamax]

austina35 said:

I would advise against using a plug thread chaser whilst the cylinder head is on the car. You will put debris into the combustion chamber and that isn't what you want to do. All that metal splinters sliding up and down with the engine running. Only needs to find the edge of the piston.......

Well, yes. But in OP's situation what would you do? Dismantle the engine or try, gently, to get a spark plug properly installed?

I'm not recommending this but if he just shoves in a new plug tight enough to work he'll probably have a car that's good for another 30,000 miles, cross-threaded or not.

IMO what's needed here is a gentle touch. Someone who can get the new plug straight enough to find the original thread and then tighten it just enough to stay in without stripping what's left of the thread.

[Lincsls1]

The stuff of nightmares!
Good luck sorting it OP.