Welcome to our resource for MG Car Information.



MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - Need engine advice...

I'm guessing the worst, but can anybody tell me what has happened?

Last day my vvc has sounded like a diesel, today there was a bang, and lots of clanking, took engine cover off to find spark plug cover has been ripped off and third spark plug is right out of engine sill on the HT lead....

what damage am I looking at and what happened??


Sounds like a spark plug has come loose and started leaking gases past it thus making a noise like a diesel. Eventually the plug has blown out. Check the thread in the head by attempting to screw the plug back in. If it still pulls out then the thread in the head has stripped and your head will have to be removed to have a helicoil insert put in. Basically the plug hole is opened up and re threaded to take what looks like a spring screwed into the thread. The plug then screws inside the spring. Or you could replace the head!

Has your car been serviced recently? If so then perhaps this was the fault of the mechanic.

Bruce Caldwell

Hi Matt

I guess the spark plug has either been over tightened or cross threaded the last time they were changed. The head can be repaired, but will need to be removed and given to a competent machine shop to do the work. The alternative is to fit a second hand head.

I would try fitting a new plug to see if it tightens, but I think the damage will be to the thread in the head. If you try this, don't stand looking over the engine when it is started in case the plug fly's out!

Alastair McLeod

on the bright side you could take the opportunity to upgrade to a high performance head, such as those at
i believe mike does them too.

well, the thread is fine on the head, the car hasn't had a service for ages, so know idea what happened.......

so does this mean all I need is a new set of plugs??
(might as well change them, the one that came out has lost it's gap)

could it of caused any other damage driving it like that?



Drop me a line if you like for a more detailed answer.

Had this happen to me last year on the way to a certain stag do!
Researched it lots and decided (for me at least) that gas flowing was the way to go.... fixing the head properly at the same time of course!!

Many people offer the service. I had my local garage (Swain & Jones) do the hard work removing the VVC head and posted it to Peter Burgess who did the head work. Posted back and tehn fitted by S&J.

Found that it would be hard/imposible to prove blame in my case. Especially as there was a 25% chance that I touched the plugs last!! Ooops!

There are other options of course...
eg. helicoil in-situ; helicoil with head off; metal insert etc.
The cheapest is to heli-coil the plug socket without taking the head off. This is dangerous as swarf can get into the cylinder. People oft pack the cylinder with grease first to stop this happening. Cheap and cheerful! 100+vat was what I was quoted.

Hope this helps.
Paul Nothard

>>>the thread is fine on the head
===sounds like you have been v lucky and got away with it Matt. Shouldn't have caused any harm, just fit new plugs and off you go...

Are you *sure* that the thread is fine?
Ali head and steel plugs often strip the last portion of the thread as they work loose - as they did in my case.

Not saying don't do it... just be careful! :o)

Paul Nothard

>>Had this happen to me last year on the way to a certain stag do!<<

LOL! And to think, that was just the start of the weekend... ;oD

Paul, how have you found Peter Burgess' work?
Rob Bell

>>Are you *sure* that the thread is fine?

Pretty sure, I tried screwing the plug back in and it does tighten right up, no idea of how long it will hold, if at all though

Only one way to find out and that's when I put some new plugs in tonight and fire it up.......



Get a torque wrench(?) when tightening up the spark plug to make sure you don't overtighten.

Good luck / fingers crossed etc!


strange...just noticed that the spark plugs I took out are Unipart GSP 9652

the last person to change the plugs was me last year and that was for NGK (NKG?) plugs

I had a head gasket done at dealership about two months ago and an MOT at rover garage last week
so someone HAS changed the plugs without me realising and it can only be from either of the two above occasions.....v strange


How many torque wrenches are there that can be reliably set to 12 Nm? Not the ones from Halfords that's for sure :o(

Anyone know where I can get one that can?
Rob Bell

I guess you really mean at Halfords prices? Else try any SnapOn or MacTools van.

>>How many torque wrenches are there that can be reliably set to 12 Nm?<<
Errrr... shouldn't it be set to 25NM for MGF spark plugs ?
My bike's plugs need tightening to 11NM and I have a really dinky 3/8inch drive torque wrench for this.
I did notice some torque wrenches in Halford's professional range today for about forty quid, and I think they went down to 20NM.


D'oh, yes, quite right Steve!

From Spyros' previous post on the topic:

VVC up to 2001MY and MPI up to 2000MY is 25Nm and gap is 0.9 +-0.1mm
VVC from 2001MY on and MPI from 2000MY on is 27Nm and gap is 1.00 +-0.05mm

Still a bit dodgy on the torque wrench I have. Thanks for the suggestions regarding Span-On John - which I think is a reputable make?

BTW, how does one check the calibration of a torque wrench? Professional spanner men get their's recalibrated every 12 months...
Rob Bell

SnapOn are "guaranteed for life" and the monkey who looks after my bike has had only one socket fail in 12 years of spannering.

Hi Rob,

It was indeed the start of a very interesting weekend! I still fond have memories of a certain "dog's dinner" shall we call it!

Anyways, to engines...

I've had the head done for some time now and have got thoroughly used to it.
Although I've not taken Peter up on the offer of a rolling road run, I can say with confidence that the engine is much much "better".
It will be more powerful I'm sure, but the main difference is with the smoothness that it goes through the rev range. There are no dips worth talking about with smooth delivery all the way. It pulls significantly better at lower revs which is wonderful.

I'd thoroughly recommend Peter and his work... although I'm not quite convinced that the cost is justified - but I did have the VVC stripped at a main dealer.

If you're down our neck of the woods, give me a shout and I can take you for a spin.

Paul Nothard


well my F once again is sat doing nothing in the driveway, the thread was stripped on the head...

Couldn't find anyone willing to helicoil in-situ,
can't afford the labour costs involved in taking the head off, so car will have to stay where it is


Hi Paul,

Since I still have some pix of your wedding using wedding cars tunbridge wells that I've yet to give you, that may be sooner rather than later! BTW are you going to Silverstone this weekend?

Matt, bad news m8 - sorry to hear that the car has to be laid up for the moment. How handy are you with a spanner? A second hand head might be one way forward if you fit it yourself...
Rob Bell


Keep asking around. It was a (decent!) MG dealer who was offering to helicoil in-situ, but couldn't offer any guarentee with it. Have checked and it was 100+vat.

Back street garages would be much more happy to do this I guess.

If the plug fails again, then it shouldn't (I think - help me here peeps!) do any real damage.

If the swarf gets stuck in the cylinder, then that's a bigger problem.

Good luck!


ps. Mailed you offline Rob.
Paul Nothard

And back to the original question...
Would running with the plug out cause any damage?
I can't see how it would directly, but bear in mind
The engine is no longer balanced and might shake violently at certain revs.
The engine is still pumping fuel and air into this cylinder at explosive concentrations which are in turn being pumped directly into the engine bay - a very small area, a K&N will suck some of the fumes back into the engine where the mix will be very rich, a non K&N system will vent these fumes around the engine bay looking for a source of ignition (eek).

If you need to drive the car with a plug out I would DEFINATLY locate the injector of that cylinder and remove the power to it, this will compleatly stop fuel from entering the problem cylinder, and you will just end up with hot air being pumpled into the engine bay.

Will Munns


How do I do that, do you mean just remove the HT lead off the coil? many thanks -matt

If you need to drive the car with a plug out I would DEFINATLY locate the injector of that cylinder and remove the power to it, this will compleatly stop fuel from entering the problem cylinder, and you will just end up with hot air being pumpled into the engine bay


>do you mean just remove the HT lead off the coil?

Nope, the HT leads only supply the spark to the plugs, the inlet manifold is a 4 half donut shapes with the chamber sitting on top of the engine and the inlet manifold joining the head to the chamber. errm
the black plastic bit!

On the LHS of this picture you can see a cable tidy going thru the centre of the 'donut' this covers the injector cables, on cyclinder one and four you should just be able to see the injectors by looking in either end, there is an injector for each chamber, the cable is clipped onto the injector with those 'push the metal clip and pull the connector' type connectos that are used all over the engine bay (you may want to practice on one of the tempture sensors which are out in the open.
I have not tried to get at the injectors myself and fear that because the third cylinder has popped rather than the first or forth you might have a job getting to them.
Has anyone got experence of getting the inlet manifold apart without taking the fuel rail off?

Will Munns

I've driven a mini with a plug out and it didn't do any additional damage (can't remember why I did this now!). It's a bit noisy, but not that rough.

The HT lead to that cylinder will still be sparking, so take care of where you put it (best remove it altogether).

I don't believe the MoT tester would have replaced the plugs, but the garage doing the head job, would probably have taken the plugs out.

You could just araldite a long-life plug back into the head, and sell it quick. It may last about 5 years like that ! (actually I think this is a better solution than heli-coiling in situ ... )


You could just araldite a long-life plug back into the head, and sell it quick. It may last about 5 years like that ! (actually I think this is a better solution than heli-coiling in situ ... )


I tried that last night with some liquid metal!!
Left it a good 24 hours but it gave way as soon as started the engine :-(

I guess not enough to bite onto on the head..

I know it sounds harsh but I only need it to work for a couple of days so I can trade the car in which is why I'm willing to take the risk of the heli-coil with the head still on, have been quoted 30 quid for the helicoil as long as I can get the car to them!

I think they must of changed the plugs when they did the HG although they never put it on the bill...crap thing is I had them put in MS's uprated gasket in at the time as you couldn't get one from Rover for love nor money, because it wasn't a 'rover part' they would not warrenty the work so I have no come back...




I had a heli-coil put in an engine in situ, worked OK. Don't forget ally is pretty soft, but its not ideal. That's what I would do.
But please advise us details of your car so that we can avoid buying it second-hand!
T Green

Heli Coil in-situ no probs - they usually have a hi vaccuum probe to remove the ali swarf after re-tapping (and the majority of the swarf collects in the tap grooves - stuck to the cutting compound.
I've done and had done a couple of my motors over the years and kept them for several years after with no problems.
Paul Lane

Driving or even turning the engine with a spark plug disconnected can cook your coil and even the ECU.

Spyros Papageorghiou

Helicoiling a spark plug thread with the cylinder head in situ should not be a problem. To be on the safe side you could connect a hose thin enough to pass through the plug hole and connect it to a vacuum cleaner nozzle and suck the swarf away from the piston crown.

It may be an acrobatic challenge carrying out the job, though, working in the engine compartment of an MGF.

And do be very careful not to drop the break-off portion of the helicoil insert through the hole into the cylinder! A threaded insert sleeve may be a safer solution.

When the topic of in-situ helicoil was raised a few months ago someone suggested taking the piston to just below TDC and filling the cylinder with grease. After fitting the helicoil, turning the engine by hand ejects the grease together with any swarf out of the plug hole.

This might wreck the cat on starting though.

You could melt the grease with petrol and syphon it out i suppose?
If you did this would you risk contaminating the oil as some petrol would seap past the piston rings?

Will Munns

This thread was discussed between 14/07/2002 and 19/07/2002

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.