Helicoil Spark Plug Inserts

[GTO Scott]

Ok, i've got a problem.

Whilst carrying out a spark plug change on the XJ (3.2 AJ16) No.2 cylinder spark plug was extremely awkward to remove, I guessed almost as soon as I started undoing it that it had gone in cross-threaded by whichever monkey installed the previous set. As I couldn't remove my spark-plug socket without retrieving the plug itself (the cross threading meant the socket was firmly wedged) I had to go for it and risk snapping the plug in order to remove my spark plug socket. Surprisingly enough the plug did not snap, but now as soon as I try to tighten up (to 12ft.lb/T) the new spark plug, it wedges the socket in place - the only way I can get the plug in is to tighten it just enough that it bites the remains of the threads in the head, but is still slightly loose. I suspect the coil-on-plug ignition module for that cylinder is also going above and beyond the call of duty by holding the plug in place.

Although I know of the existence of them, I have never used helicoil inserts, which would appear to be a cheaper solution than pulling the head in order to drill and tap the spark plug hole, or worse replace the head.

How hard is a helicoil to fit, and is there a decent step-by-step anywhere?

Thanks.

[GavinPearson]

I would take it to an engine machine shop and get them to do the work. Hopefully they can do it in-vehicle.

A helicoil will work, as the plug isn't taper seat, but it's not a great solution - it may wind out.

If you do have to remove the head then ask for a timesert - it is the best technical solution.

[Steve_D]

If you needed convincing I agree with Gavin.

Helicoiling a spark plug is not for helicoil virgins. Helicoils can be a pain in the butt just fitting them to a hole in a piece of plate let alone down inside the casting and with the head in place.

For your info/education the process involves tapping the hole out to approximately the next thread size up and fitting into it a coiled, diamond section, wire.

Steve

[Simon Says]

Wurth Timesert can be done with head on car and far superior to Helicoil in my opinion,most good workshops can carry this out for you if its done by the letter its fit and forget i have fitted these since circa 1993>

[dcr]

+1 for Timeserts , not had any problems on the ones I have done over the years

Dave

[steveo3002]

GavinPearson said:

I would take it to an engine machine shop and get them to do the work. Hopefully they can do it in-vehicle.

A helicoil will work, as the plug isn't taper seat, but it's not a great solution - it may wind out.

If you do have to remove the head then ask for a timesert - it is the best technical solution.

what happens when a helicoil does wind out? i had one fitted to a plug hole and fear it might unwind nixt plug change ? can i refit it or what

[Steve_D]

steveo3002 said:

GavinPearson said:

I would take it to an engine machine shop and get them to do the work. Hopefully they can do it in-vehicle.

A helicoil will work, as the plug isn't taper seat, but it's not a great solution - it may wind out.

If you do have to remove the head then ask for a timesert - it is the best technical solution.

what happens when a helicoil does wind out? i had one fitted to a plug hole and fear it might unwind nixt plug change ? can i refit it or what

Time to fit a timesert. A helicoil will be fubar if it winds out.

Steve

[steveo3002]

so the helicoil will be toast...would the threads remain usuable?

maybe it will be okay...i spose it will wind out one rainy night lol

[premmington]

I've been in the trade 25years, helicoiling anything is bad news, timeserts are far superior.











http://www.remmington.plus.com

[Pupp]

If needed, another endorsement for Timeserts. Clever and effective; fit and forget

[GTO Scott]

Ok, sounds like a Timesert is the way forward then.

Now to find a place that can fit one....

[Pupp]

GTO Scott said:

Ok, sounds like a Timesert is the way forward then.

Now to find a place that can fit one....

Maybe contact Wurth and ask for a list of local outfits they supply to who go through lots of 14mm inserts? Worth knowing they come in long and short variants too...

[Pumaracing]

Sounds like your first step is to buy a decent quality socket. Good ones don't wedge on tight like that. Yours is clearly oversize as made or worn. I once had a cheap plug socket bought as a stop gap measure from the only place that was open at the time that did the same but its quality replacement worked perfectly. There may be nothing wrong with the thread in the head. Plugs can stick pretty badly if they've been in a long time, corroded a bit or just been overtightened in the first place.

Hex sockets grip better than 12 point if you can get one but anything of good quality ought to be ok.

I'm rather surprised that no one who's responded has actually spotted that there's nothing in the OP's post to confirm the thread is stripped - merely that he can't tighten the new plug up properly without the socket jamming on it.

Examination technique 101 - first read the question properly.

Edited by Pumaracing on Friday 23 October 10:21

[GreenV8S]

If you're right that it is cross threaded, There is something called a reverse chaser which cleans up the thread from the bottom up. This would be easier to get started on the 'good' thread and save lots of struggling to get it engaged on the bodged thread at the top.

[GTO Scott]

I'll recheck the old plug, from memory (I am not by the car at the moment) the threads on the old plug were not good. Socket is a Draper 1/2" drive 14mm spark plug socket, hex rather than 12 point, which has fitted perfectly on the other 5 spark plugs, and has never jammed before on any other car (and it's seen use on a lot of different engines!).

I'll check out the reverse thread chaser - hopefully might just be the answer.

If it comes to pulling the head, i'll just buy another lump - it'll be cheaper and quicker.

Thanks for all the advice, much appreciated.

[Pupp]

Pumaracing said:

I'm rather surprised that no one who's responded has actually spotted that there's nothing in the OP's post to confirm the thread is stripped - merely that he can't tighten the new plug up properly without the socket jamming on it.

Examination technique 101 - first read the question properly.

GTO Scott said:

the remains of the threads in the head...

[Pumaracing]

Pupp said:

Pumaracing said:

I'm rather surprised that no one who's responded has actually spotted that there's nothing in the OP's post to confirm the thread is stripped - merely that he can't tighten the new plug up properly without the socket jamming on it.

Examination technique 101 - first read the question properly.

GTO Scott said:

the remains of the threads in the head...

That's just an assumption about the threads in the head. It doesn't explain, and in fact clearly has nothing to do with why the socket jams on the plug at only 12 ft lbs. That's barely more than a decent pull on a 10mm ring spanner. All I'm reading here is that the plug can't be tightened because the socket then won't come off it - nothing about the threads in the head being badly enough stripped to stop the plug tightening up.

[Pumaracing]

I'm going to change my diagnosis here. It makes no sense that the socket jams on both the old spark plug and the new one but only in this hole and not on any of the other plugs. I bet the socket is jamming in the bore in the cylinder head and not on the plug at all because this bore is machined a tad smaller than the others and the socket is too large on the o/d. I suspect that spark plug was never tight in the first place and there's nothing wrong with the threads in the cylinder head either. I'll wager all we're doing here is chasing round in circles after an assumption made by the OP that was never valid in the first place.

[Pupp]

It's indicative of a cross threaded or stripped scenario. Chasing it, re-tapping, whatever will only end up reducing the interference and hence the mechanical security that the plug ultimately has. Ok, it might hold, it might not; the thread will still be suspect and a Timesert will fix it. No brainer

[spend]

Just use a long bolt to distinguish between threads or head fouling socket. You can also see much easier with a long bolt if it is skewing as you go into the thread. Any decent fastener place should be able to match the thread up for you, just fine metric IIRC.