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MG MGF Technical - Spark Plug blown out

I am wondering on where I stand on the above problem.

Yesterday I was on my way home when I heard a bang from the engine, followed by what can only be called a loud rasp. The engine was still running, but was not smooth. I called the RAC, when the patrol man arrived, he knew exactly what it was - the spark plug from one of the cylinders had blown out !!!

When trying to refit the plug it was found that there are no threads left on the cylinder head for that plug.

Since I have only ever have my car serviced at MG dealers, never tinker with it myself, and the spark plugs are supposed to be fitted ever 60K miles, I cannot see how this is my fault.

I had the obligatory HGF at 60K - so I assume that this was the last time the plugs were changed.

I am currently awaiting the bad news, but I am fearing that it will require a new Cylinder Head.

Has anyone else come across this problem and what was their outcome...

Allan Inness
N850 TAY
Allan Inness

If the plug thread has gone, the magic word is Helicoil.

Helicoils are effectively replacement threads in the form of a spring that can be fitted, after some machining in place of a damaged thread.

Hard Luck!
I had a similar problem with a Merc, the ally cylinder head doesn't help.
IN my case it was down to a lousy mechanic at the last service, but you try to prove it!!
I would go back to the garage who last changed the plugs and make a formal complaint, talk solicitors etc.
Helicoils are an answer but they need good access to fit and should really be done with the head off, to make sure no swarf gets put into the engine.
The helicoil fitting device has a long rod and you need to be able to be absolutley sure you can get the correct line into the hole.
In fact, I had my Merc done with the head on, and seemed to be OK with no problems. (Aluminium is fairly soft stuff - but the car had done about 150,000 miles!)
In view of the temperamental nature of the K series, I would tread carefully and if you can get the garage to play ball, go for a new head (and latest head gasket!).
T Green

A few years back graham Bishko had this happen and he sent the head away to be repaired - not sure who did it but it must be in the archives somewhere.

Allen - I would certainly have a go at the garage that did your least service - might not get you anywhere but it is worth a try especially if the last time they worked on the engine was within a reasonable time/mileage scale.

Ted Newman

>>> new head (and latest head gasket!). <<<

Regarding the head gasket, I could tell you that Raceline provides new steel headgaskets for the 1.8 K-series.

Read that in CCC, although the website of Reaceline ( doesn't tell a thing about supporting the K-series with that gasket.

This gives us:
Mike Saturs Competion Head Gasket: 60
Racelines Supersteel Head Gasket: 150


As Ted mentioned, Graeme Bishko had exactly the same thing happen to him. To to a lack of the correct spark plug spanner, one of the sparkers was presumably inadequately torqued into the head- as a result it launched itself from the head. The only thing that stopped it obtaining a low planetary orbit was the engine cover that had an impressive dent to show for the energy it absorbed...

As Brian mentioned, he had the head helicoiled- arranged through some friends at K&N R&D in Warrington.

Where do you stand WRT the bill for all this work? Good question. Clearly, the spark plug was not correctly torqued down- but prooving culpability will be very difficult I suspect (but I am no lawyer).

Rob Bell

>> Mike Saturs Competion Head Gasket: 60 <<
Just to correct this, Mike's HG is 25+vat, which isn't 60 ;)

Steve Childs

Well I have got the diagnosis and costs...

New Head fitted - 1385
Helicoil fitted - 750 (they will remove the head)

I am now working on who is going to pay for it.

Is there any numbers I can ring for Rover/MG to speak to someone about this.

The MG dealer who did the HGF 12months ago, also broke the throttle body, and couldn't find the problem - even after 2 days.

Another Dealer looked at it for 2 hours, ordered the part and had it fitted the same day !!!

I sent the bill to the original garage to be payed and they paid up... Is this enough grounds to prove poor workmanship in the initial job and to relate this problem to their work?

your comments are eagerly awaited....

Allan Inness
N850TAY - stationary at the moment....
Allan Inness

Out of interest, the MG dealer who did the HGF 12 months ago, did he do a 60K service and then the HGF occured shortly afterward? Or did the HGF occur before / or a long time after 60K service?

Steve Childs

The HGF happened the day before it was booked to go in to the garage for it's 60K service.

It happened at 59995 miles on the clock.

The car now has 79K on the clock.

Allan Inness

N850TAY - still stationary
Allan Inness

>>> Just to correct this, Mike's HG is 25+vat, which isn't 60 ;) <<<

Dooohhh.... maybe it was 60 to have it sent to Belgium and with all the taxes. Anyway, sorry for spreading wrong info about that.
The one from Raceline is remarkably more expensive.


The only reason to talk to Rover is to get them to censure their dealers - but will this have any effect?
Unfortunately the problem amy have been some time ago. What happens is that the spark plug is put in crooked and cross-threaded - it can ususally still be torqued up to the correct torque the first time. However, when it is removed again it brings all the threads with it and will not tighten properly. Either way, it is usual for no-one to say anything about it for obvious reasons!
I would try to get your garage to confirm the problem in writing and send a copy to the garage that has done the work, possibly with a solicitor's letter. If you belong to RAC or AA their legal depts may well help. Good luck
T Green

I had a helicoil fitted on a beetle at the dealer a few years ago, after the threads went. I thought 30 was steep at the time, but 750 seems too much.
Nathan Carnie

750 is a lot, but I suppose if you have to take the engine out and/or the head off, that must come expensive.
T Green

A little tip an old mechanic gave me years ago about fitting Helicoils in plug holes with head in situ. Turn the engine over until the offending cylinder is at bottom dead centre. Fill the cylinder with grease using a grease gun. Cut the new thread for the Helicoil. Fit the Helicoil. Turn the engine back to top dead centre thus pushing any swarf, muck etc back out of the hole. Redo the grease bit again if thought necessary.
Bruce Caldwell

PS On the compression stroke off course, otherwise the muck may go out through the valves!
Bruce Caldwell

the helicoil spark plug kits are around 50 UKP.
Is the grease trick okay with the cat ? I would want to run the engine on the starter - without any plugs - just to make sure it cleared.


I agree, it's best to make sure it's totally clear. Perhaps a bit of petrol down the bore and then blow it out with an airline if possible?
Bruce Caldwell


If you have a VVC engine (ie coils instead of distributor) NEVER run the engine without a spark plug or with a plug lead removed unless you either disconnect the coil's low tension or fit a loose grounded spark to the lead. Otherwise the the electical stess may destroy the coil or the ECU - both quite expensive.

Spyros Papageorghiou

an excellent point; I do have a VVC, and running on the starter - such as for a compression test - I would probably disconnect the LT side of the coils - or try to find some dummy loads. Ideally the fuel injection should also be disabled. I would guess that TestBook disables these in the workshop.

any progress on getting the car back on the road ?



I am still waiting -

The garage said it would be friday by the earliest, time they ordered the new head and had it delivered.

I am still working on getting the garage that did the HGF to pay.

I already have a previous greivance with them on their standard of work at the time of the HGF. No one else has touched the plugs since then - so i am trying to get the garage who are doing the work to write their opinion on the state of the head and what caused the problem.

I will then go and see the manager of the garage that did the HGF and state my case... if push comes to shove i will seek legal advice from both my insurance company and the RAC. and maybe take it to small claims court....

Or alternatively I can shout the showroom down and post derogatory remarks about the dealership on websites, all of which will hurt thier sales much more than paying up !!!

I will see how it goes...

Allan inness
N850 TAY - missing driving it ....
Allan Inness

Well, I got the car back on Friday night..

What a difference - I don't know if it is because I was having a problem, or whether it is because it is a new head, but he car feels like new.... It certainly seems a bit more perkier..

The bad part was the 1400 quid I had to fork out.
I am still trying to get some kind of refund.

Allan Inness
Allan Inness

I thought the small claims court had a limit of 500 for a claim?

Steve Childs

This thread was discussed between 20/08/2001 and 28/08/2001

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