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Really Loose Spark Plug


Isaac Hunt
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My Daughter left her Fester 2.0 with me for the weekend for a bit of brake work.

Before I moved it off the road and onto the drive, I checked the oil for her, all good, she does check it and top up regularly, 150k miles, uses a bit thee days, TADTS.

Started it up, fires up ok but I could hear this knocking, that’s not right.

it sounded quite dull, but not big end type rattle, more top end, but not cam type rattle, seemed to be coming from clutch end No4.  Mmmmm, sounds a bit plug blow by I thought.

So off with the air box, mmmm, why is No1 plug lead not in the recess like 2,3,4.

Kinell, No1 plug has almost wound itself out.  It was caked in soot.  I cleaned it up, put it back in.  It nipped up OK and the knocking had gone.  

Never had this happen before, although rather ashamedly, i’ve never touched the plugs in this, so they’ve been in for at least 60k.  I’ve sort of got used to these ‘whatever tipped’ plugs running big change mileages and whilst oil and filter gets done regularly, spark plugs sort of got overlooked.

I don’t know how many threads it was hanging in by, but there was no misfire or hesitation.  The noise was travelling, appeared to be coming from No4 end, but No1 was the issue.

Noise had only been there for the last two days apparently.  I don’t know how many threads we were away from the plug being blown out off its socket, but pretty close judging by how proud the HT lead was.

 

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Could be a previous mechanic leaving it very loose and getting distracted? Better than my old VW bus where I found the plug still on the lead flapping about with all the ally thread from the head on it!

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5 minutes ago, willswitchengage said:

I once had a spark loosen itself through life it fired out one day causing a bit of a bang under the bonnet. Luckily no thread stripping or lead damage, I just had a spare which I screwed back in and all was good. Hopefully yours will be as easy...

Same happened with a Corrado I owned years back. Driving through Dorchester, large bang and engine sounded unwell. I pulled in and quickly discovered one of the plugs had loosened and fired straight out. It hit the underside of the bonnet with such force it left a dent in it, despite landing in sound deadening sponge at the start of it's journey. 

I wound it back in by hand, tightened it with a socket when I returned home and it was fine for the rest of my ownership.  

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I had one pop out on my Uno years ago while driving up the A11, my fault as I'd just serviced it, was always a bit wary of overtightening plugs and had obviously been a bit over-cautious with this one. Loud bang, even louder engine running on three (who'd have thought!), fortunately the plug was still attached to the HT lead so back in it went, definite brown trouser moment until I realised what had happened. Glad you spotted it early and hopefully avoided any such drama.

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Yeah, my old Saab did the same, except it also broke the coil pack in half too - the pencil coils are screwed down so it couldn't shoot clean out.

Unfortunately it happened near Hannover, Germany and caused the car to be scrapped as the breakdown people refused to recover it, and the garage it got towed to were just going to screw the plug in as hard as they could and send me on my way for the sum of £600. I'd have probably OK'd it if they were going to properly helicoil the head but they said they wouldn't do it, even in situ, so it got fragged.

I now check my spark plugs twice a year to make sure they've not decided to wind themselves out while I'm not looking. 

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I had the centre core come out of spark plug once when removing a plug.  It was recessed in a Dolly Sprint engine.  It left the thread in the head.  I managed to get the thread out with an eezi out on the end of a socket, considered my luck was in that day.

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31 minutes ago, Richard_FM said:

I don't know anybody this has happened to, but I've heard of someone with a Triumph Herald who had a fan blade detach itself & shoot right through the bonnet!

Happened to a cousins Hillman Avenger way back when I was a lad,shot out through the bonnet leaving a jagged exit wound,taking the top rad hose out at the same time.

It was unceremoniously dragged home behind a Massey Ferguson 35,had a second hand rad,hose and fan blade fitted,and the gaping hole was delicately twatted back down with two lump hammers and left at that,no paint or filler,and it was pressed back into service,it lasted another few years after that,before being put out to pasture.

Have fond memories of that old heap,it was fitted with a slightly hotted up 1.6,and tended to be driven quite enthusiastically.

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7 hours ago, Richard_FM said:

I don't know anybody this has happened to, but I've heard of someone with a Triumph Herald who had a fan blade detach itself & shoot right through the bonnet!

Had this twice on a pinto with aftermarket plastic fan.

Luckily when racing and never when using the timing gun

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