Damnit, I went out this afternoon with my new plugs and wires... FFS how am I ever going to get my shovels in to the coil packs? I think it might be just plugs this time :/

Hasn't her indoors got small hands and a pair of Marigolds?

I seem to remember on mine (GEMS) pulling the coil packs up for better access. I don't remember that being difficult.

GEMS is dead easy as the wires go straight in the top. On a Thor the coils are hidden down the back so nothing like as simple to get to.

It is possible to wiggle the coil packs out towards the (RHD) passenger side of the car. Or to the left of the engine, as seen from the drivers seat, for the pedants.

It is a ballache but it was possible on mine with LPG tat in the way. Depending on your setup it might not be.

I believe I had the upper inlet manifold removed too at that point, which opens things up quite a bit - might not even need to remove the coils.

It looks like the inlet manifold may be coming off. Is there a gasket I need to get?
Realistically, I need this on the road on Sunday so it's getting plugs now and wires are going on the One Day list. I might just leave them on the back seat the next time it goes to the garage - they know I only leave them the fun jobs :)

Technically yes, Thor has a metal gasket between the upper and lower manifolds that should be replaced, though I've had mine off many times and only replaced it once when I actually remembered to get a new one!

Well, turns out I can't even change the damn plugs :(

The second plug I tried (no 5) was cross threaded or something - I had to use a bar to get it out. As you might expect the thread is a mess. I cranked the engine to try and blow out the pile of crud/alloy shavings that covered half the hole. Now I've got a very second hand looking thread and a spark plug doesn't feel like it'll go in properly.

Has anyone tried chasing the threads with the head in-situ?

There'll be more helpful replies from others but - I've noticed on P38's some (wider?) plug sockets tend to foul against the side of the plug hole which can lead to cross threading when putting plugs in. Would think the coil pack access problem (least of your problems now) could be overcome without removing the manifold, can get down the back of the Thor manifold with a couple of 1/4 drive wobble extensions and 8mm (iirc) socket to allow unbolting the packs to move them for better access. Never owner one but have changed the plugs on plenty P38s including more than a few with difficult threads that might have been damaged by someone using the wrong tool previously, never had to use a chaser though.

Yes. Get an old plug and use a hacksaw or thin cutting blade on an angle grinder and cut a slot along the length so it becomes a sort of crude tap. Run that down the thread to clean it out. Spin the engine over to blow any crud out and then carefully put the new plug in. I always put a smear of graphite grease on the plug threads to help them go in nice and easily and to stop them welding themselves in. If you don't have graphite grease, Copaslip is almost as good. Don't go all gorilla when you do it up or you could end up with no thread at all but if you read the instructions for putting plugs in (which nobody ever does) they don't need to be ridiculously tight anyway. Worst case, one day you will be driving along and the car will suddenly drop to 7 cylinders, sound like a traction engine and you'll find the plug has made a bid for freedom and is dangling on the end of the HT lead. I've only ever known it happen once and that was after a plug thread had been completely stripped so the plug could only be done up finger tight anyway (and it was on a Vauxhall).

OK thanks folks. I found that hack on a YT video for lawnmower etc but didn't feel confident to do it on a proper engine.
And yes, I always read the instructions (have to, really, if you work in IT) so I don't gorilla plugs. This is the first set I've fitted on this engine so I forgot how spoilt I've been by replacing my own work on my Jeep!
There are some idiots out there. Now I remember how hard it was to get the oil filter off the first time, I shoudn't have been surprised :/

Ok, here comes the teeny dremel and cutoff wheel.

EDIT: Wish me luck!

Good news, I think there's enough thread to save it. Bad news, I can't work with the standard plug socket I've got. FFS, isn't anything standard?

Have you got the smaller holes that some later Thor cars have? Where you can't fit BPR6ES plugs because the hex is too large? If I remember right, the late Orangebean had one hole that was smaller and Rutland Rover had to get the alternative PFR6N-11 with the smaller hex.

Well, I've got 8 spark plugs in the engine. 2 of them are even new! Let's see how long they stay there. So that's 2 plugs and 0 wires complete. I rock!!
Thanks for the help and support, I really didn't want to contemplate a head off job.

Richard, that sounds exactly right and the Duchess is a Y/01 car. No 7 went in fine. No 5... not so much. Thanks for the NGK part no - I'll be getting a set of them instead! (although I'm half tempted to get the stupid price "LPG" plugs and hope they really do last a lifetime).

I went to the local car parts shop and the owner/manager bloke is an ex P38 victim. While we examined my plug socket for alternatives (turns out mine is already a thin wall one) he did say that he had bought plugs with a smaller hex for his car before he flogged it. They're all D2 owners in that shop, so quite handy. In the end he sold me a set of tube spanners for £9 which did the job on No.5 and kept my improvised thread chaser straight enough.

Don't get the LPG plugs, if you do want something that will last a lifetime (with the sort of mileage you do) get the Iridium equivalent, BKR6EIX-11. Should be good for about 40,000 miles (which is only 2 years for me).

If it comes to the worst case, those spiral helicoil things do work, I had a plug make a bid for freedom on the Galaxy some time back and had to helicoil the remains of the thread in the head. Didn't want to take the head off as its a complete pain to do on that and would have involved buying head gasket etc, so thought it was worth giving a try. Not sure it made much difference, but the vacuum cleaner and some small pipe got used to pickup anything loose, and greased the tap beforehand. Its been fine since.

Its possible on the Disco (but an utter pain to do so) to replace the coil packs without removing the upper manifold. I'm led to believe that the P38 has a bit more space back there to make it slightly easier, but I managed on changing the second coil pack when it failed to do so by lying over the top of the engine and unbolting it from the bracket, then sliding it out to the side. You want to do it with a reasonably cold engine though obviously. Helps somewhat to have something to lie ontop of the engine if your doing that, and you might just find it easier to take the top manifold off instead (be aware that the bracket that holds the coil packs to the engine also attaches to the manifold so you will need to remove bolts from that as well - which are easier to find once you know they are there and start looking with the torch for them - if i remember right there are 3 of them, one in the middle on the top that you can see, and one either side at the bottom which are much more difficult to see)

there's a tool for that (helicoil 5334-14 sav a thread ) this tool is 14mm/1.25 pitch not shore its the correct thread size but will give you the idea . if you require to do this put piston as close to top as possible and use grease to collect as much of the cut material as possible , a piece of wire with grease on it can be used to collect any material in the bore . cut 2 threads and remove tool and clean reapply grease and do agian untill all threads cut , its not a hard job just time consuming

The PFR ones are platinum, and should last 100,000km apparently. That's 4 years for me. The only thing is they are 1.1mm gap and you cant gap them.

But.... as long as they don't knacker the heads I guess they're a good choice.

The old plugs were definitely the wrong sort of champions, I hope the rest come out OK when its time :/

Running on petrol platinum plugs outlast nickle several times over and iridium outlast platinum. Running on LPG platinum will still outlast nickle but allegedly (and I'm not clued on the science) platinum interacts with the LPG burn process (eaten away when running on LPG) meaning platinum doesn't outlast nickle by the same factor as when running on petrol. Old advice used to be platinum doesn't last as long as nickle on LPG! I've found that in practice platinum plugs do still outlast nickle by a similar factor as when running on petrol, just that both type's lifetimes are shortened. There's no alleged chemical interaction with iridium plugs running on LPG and iridium is a tougher metal than platinum anyway, so if iridium cost 30% more than platinum they're probably still worth it in terms of price and avoiding the effort (and maybe also risks of damaging threads further now in your case) for the long term. As Gilbert said post#15 some of the LPG specific plugs, especially LPG specific brand plugs such as Brisk, can give terrible performance causing misfires etc on both LPG and petrol. 'Normal' brand plugs such as NGK aimed at LPG (NGK do LPG specific iridium plugs with something denoting LPG printed on the plug) can be good but such plugs are often just the same as the manufacture's iridium equivalent (of a nickle/platinum) plug just without the LPG code. If a manufacturer makes an iridium equivalent and an LPG equivalent they're probably really just the same plug but the plug without the LPG code may be quite a bit cheaper.

As you know I've converted a lot of Nissan Elgrands and own one myself, a real pita to change plugs on these as the wiper mechanism has to come off, then engine brackets etc, even then access is still poor because one bank of plugs is partially hidden beneath the manifold. Far easier to change plugs when the manifold is off, so a lot of owners have me swap plugs at the same time as LPG conversion when manifold is off and access is very easy. On these I fit Denso double iridium plugs, both the anode and cathode are iridium. The first time I fitted them was a gamble, no way of knowing if they'd work well, pleased they did or would have had to fit new standard plugs (which are platinum on this motor) or try a different type of iridium (most likely NGK's iridium version of the standard platinum plug, but they're often unavailable, very expensive and only single iridium).

Well, the standard Nickel ones are £2.20 and the Platinum PFR ones are £7.14. I'm certainly not going to take the two new BPR6ES ones out now, but I can't see any point in risking the head for another £42 so I'll buy 6 Platinum and run an odd set. Now I know what caused the problem - 21mm (actually 13/16ths despite being French) hex plugs instead of 16. The access to the heads looks pretty good, I'd forgotten all about the thread when we first "discovered" the issues with Thor heads and standard sized plugs and tools :/

All I really need to know is the expected service life of the PFRs when running LPG. Or I'll pop one out every 10k and have a look. My only real concern is whether the 1.1mm gap will put a strain on the ignition system, I've been gapping the standard plugs down to 0.7mm which works really well for LPG.

Richard, your recommended BKR6EIX-11 are £9 which seems like a good deal as long as they don't end up rusted like the old Champions that need to come out! I've no idea if they're double or single Iridium but if they last significantly longer than the Platinum.. got to be worth it?