IANS2RST

iTrader: (1)

developed a missfire on my saph at donnington last weekend found out it was because of 1 of thespark plug electrodes breaking off. I think it did leave via the exhaust because someone saw something fired out the tail pipe & couln't pick up anything in the bore with a magnetic pick up tool.
have done a compression test & still have 185 psi on all cylinders, turbo boosts fine, no smoke or noises.

could it have done some internal damage or I have i been very lucky?

Mike1

What sort of plug was that?

IANS2RST

iTrader: (1)

071's

Mike1

What size gap were you running out of interest?

IANS2RST

iTrader: (1)

0.6mm they have been spot on, last 4 track days

Lee_R21Turbo

iTrader: (1)

Yeah sounds like you've been VERY lucky......I had the tip off a ShitFire plug come off & melt its way through an exhaust valve on my first 21Turbo - back when I was young & didnt realise there were different heat rated plugs...oh & before I realised that SplitFire plugs were a load of advertising hype load of my arse pieces of CRAP!!!

CossieRich

iTrader: (1)

You got lucky.

Mike1

What would cause such a failure to a plug that had been running for that long? Indetectable det? A sudden weak mixture on that cylinder?

Lambchop

iTrader: (1)

That's the million dollar question
I'm in a similar boat to you but havent investigated the problem. I got a reek of smoke out the back then cruised home the last mile and switched off. Number 1 lost the tip of the plug I'm praying the piston isn't holed but wont know till i remove the head. Havent done it yet because it'll turn into a money pit and i need money elsewhere just now!

Mike1

Out of interest what plugs and what gap were you running?

Lambchop

iTrader: (1)

NGK BCR8ES and i'd be guessing the gap...hmmm....honestly i cant remember

So your engine is ok and im praying mine is too but what happens if you throw in a new plug and a month later the whole engine melts?
I've spoken to someone else on here who melted a plug, tuner checked and found nothing wrong and no det etc then 2 weeks later complete melt down. I cant afford that!!!!

IANS2RST

iTrader: (1)

I was on my 6th session of the day flying round donnington & the plugs had been in 18 months. was flat out in 4th at 24psi held when it started to missfire

Lambchop

iTrader: (1)

similar to me but i was in 5th at 145mph having accelerated from say 15mph in 2nd. I coasted down to 70mph and all was well. Then all of a sudden smoke out the back. All fluid levels are fine though and all gauges temps/pressures etc were as they should have been!!!

Bastard car.

Mike1

Isn't that NGK the one for a stock 2wd engine? Did you run a smaller gap than stock engine? Were they gapped correctly when you put them in do you know?

Are the 071s more prone to failure than the older superseded 701s? I've heard they have a shorter working life - is that because they are side gapped?

Lambchop

iTrader: (1)

They are the plugs recommended by my tuner and have run them on my rst and all 3 cossies before.

Yes they were gapped correctly because they were not long changed. I had a fucker of a missfire where EVERYTHING was changed and it was eventually found to be a dodgy petrol tank

Have you got/had a similar problem that you're asking Q's?

Mike1

Looking at both failures it seems they may have occurred when the car was held on boost for a while. Could the failures have been attributed to a mixture problem at high revs ...i.e lean ...causing extreme heat.
Would that NGK you used have been slightly too "hot" a plug for that boost Lambchop? Or was it recommended to you?

Edited to say you beat me to it with your reply Lambchop!!

I wasn't saying you had the wrong plugs/did something wrong by the way - was just interested in what happened - possible causes.

IANS2RST

iTrader: (1)

didn't get any smoke just the missfire, heard a whizzing sound which coincided with something bright orange flying out of my exhaust
have an afr meter in my car which was showing well into the green
have got a new set of plugs fitted & all seams ok.
coming off the road soon for some bodywork anyway & will be checke over before it sees a track again

Lambchop

iTrader: (1)

Could be but fuck knows!

Next time i get tuned instead of my usual fuck it give me max bhp attitude i'll knock it back to a safer zone