Anyone Seen This Before?

[DrSarty 90 1 Cars]

It seems to be my Mi's lot in life to run on 3 cylinders. It did once first built (thread on forum 'misfire') and was down to an injector delivering 50% the fuel as the others. Found, fixed, sorted.

 

Now, after an emotional blat down the Buckinghamshire lanes, when winding down, a mile from home - urgghhh, back onto 3 cylinders. Now recently my dizzy cap had exploded (!), back onto 3 again, which seemed to have been caused by my rotor arm working loose. New cap on, sorted again. We like 4 cylinders .

 

Well I retightened it planning to replace it (the arm), and then the Buckinghamshire blat incident. I thought, yep, know what that is and got a new rotor arm on. No damage to cap this time. Arm was looking ropey, but the swap didn't fix a thing...still lumpy.

 

As it was dark and was nosing, I noticed no4 end (under the plastic central cover on the cam cover) visible sparking. Oooer! Off with the cover to see grey smoke charring around the plug hole end and cam cover near no4 end AND a blown up (holes in it, shielding off too) HT lead rubber boot!

 

On removing the plug, I saw this:

 

&

 

This is my no4 plug, with the 3 prongs mated to the central electrode, almost looking like it's taken a wack!

 

Penny for 'em please??????

 

DrS

Edited November 28, 2006 by DrSarty

[jim21070 2]

Umm, interesting. Hard to say but it has not been struck otherwise the centre electrode would have shown more damage that it does and it would be squashed.

 

One injector 50% down you say. Was it the one on this pot? If so, weak mixture leading to an overheating plug that heated the electrodes sufficiently to go so soft they blew togeter in the cylinder turbulence. Maybe a bit of detonation helped to do this too but there is something not quite right with the looks of it. It is too clean. If the above were the causes I would have expected to have seen some other classic tell-tales on the electrodes. Has it been cleaned or is that how it came out?

 

I'd be suspecting an air leak on the inlet side of that pot as a possible cause too. How do the others look in comparason?

 

What make of plug?

[DrSarty 90 1 Cars]

Thanks Jim, that's a really considered and educated reply.

 

Now, yes, that was the pot that had the underperforming injector, but that was a long time ago.

 

NGK original plug is how it came out and other plugs haven't been checked.

 

The air leak (inlet side of things) is a very interesting point, as there has been a chuffy kind of blowy kindof tappety type of noise from this end of the engine which has steadily been getting worse. Whilst doing this tonight, I noticed on a bit of protruding inlet gasket right near the end a kind of sooting. This very well could be the cause of this and the chuffing noise. Could this be fixed (potentially) just be retorquing all of the inlet manifold bolts in a logical order?

 

Cheers Jim and other contributors.

 

DrS

[Alastairh 47]

hmm strange.

 

I've had one of the little prongs brake before in my old 106 xsi, which shorted out and took the ignition amp and coil pack with it.

 

Alastair

[welshpug 1,657]

looks nasty and you caught it in time, just use the Standard NGK single electrode ones, they perform better than the triple electrode ones as theres more airspace around the spark.

[DrSarty 90 1 Cars]

Standard NGK single electrode ones

 

Part number pls anyone?

 

DrS

[welshpug 1,657]

champion code is RC7BMC, I think NGK uses the same or similar number, GSF will know what you need anyway.

 

Gapped to 1.6mm, but they are nearly all factory set to that already.

[hengti 2]

according to piccie, you're using BCP 7ETs - could try BCP 7EX or BCP 7EVX - both are single electrode - EVX is NGK's platinum plug, which is much more expensive but runs much sweeter imo (well, it does in the 8v anyway)

 

ed. sorry - as per Welshpug below - i meant BCPR 7ES - not BCP 7EX (BCPR 7ES is the std NGK plug for the 8v). I'm sure BCP 7EVX is the code for the platinum equivalent though.

just out of interest - NGK plug code guide here

Edited November 28, 2006 by hengti

[welshpug 1,657]

actually, a handy old GSF catalogue reveals NGK number BKR6EK, GSF code T92704 which is actually the same as all 406 XU engines 96 onwards.

 

but thats for a 2.0 iron block engine.

 

1.9 uses BCP7ET, GSF No N92726 if it had no cat, or BCPR7ES, N92728 if it was one of the rarer 1.9 16v cat engines.

 

and as HENGTI just pointed out and I've only just twigged is that those BCP7ET plugs are standard for that engine!

Edited November 28, 2006 by welshpug

[DrSarty 90 1 Cars]

Yep. I have the 7ET standard (triple prong jobbies) and have since heard that the singles are a better idea. I'll follow your advice when replacing but am particularly intrigued by the possibility of a leak inlet side near that cylinder (no4). I did ask if tightening was ok or should I have the inlet side off, re-face and re-gasket?

 

Your thoughts geysers pls.

 

DrS

[jim21070 2]

Yep. I have the 7ET standard (triple prong jobbies) and have since heard that the singles are a better idea. I'll follow your advice when replacing but am particularly intrigued by the possibility of a leak inlet side near that cylinder (no4). I did ask if tightening was ok or should I have the inlet side off, re-face and re-gasket?

 

Your thoughts geysers pls.

 

DrS

 

I'd have the inlet manifold off Dr S, clean up, check the faces and put on a new gasket. It's not worth the risk to try to reclaim what you have. A leak resulting in a weak mixture can do all sorts of nasties.

 

I always put the gaskets on with a little smear of grease, vaseline is my preferred choice. Then evenly torque down the fasteners and job done. They need to be tight enough but not too tight. After a week or so go back over them and re-tighten them to account for the gasket compressing and settling in.

[DrSarty 90 1 Cars]

My situation is worse - mush worse - the head must come off!

 

I was grateful for everyone's replies, Jim's inparticular. Anyway, after telling my wife I'd be 10 mins to fit new HT leads and 4 new, single electrode plugs to get a running engine again before doing the inlet manifold thingy, I found that plug 4 just slots into the threaded plug hole in the head - all the way in - no tightening and barely touching (what's left of) the threads.

 

For good measure!

 

What has happened. Clearly the head must come off, but {A} has this happened before {B} what caused it {C} can the spark plug hole/thread be repaired (i.e. is it an insert?) and {D}

 

WHERE CAN I GET ANOTHER Mi HEAD FROM PLEASE????????? ANYONE

 

Really upset now, although the head needed to come off soon anyway to fit the Maniflow system (head to tail) I got from Batfink and the new inlet cam & thin gasket I'm getting from PeterT. But how much of my money is gonna be needed to repair/replace the head.

 

What has happened and why me?

 

DrS

[nick 3]

The spark plug thread can be Helicoiled (Old thread drilled and a new steel thread inserted) quite cheaply. Most garages/machine shops should be able to do this for a few quid.

 

Nick

[jim21070 2]

Yep, no worries at all. Helicoiling is excellent. Many moons ago back in my young days of Japanese Motorcycle ownership I even invested in my own helicoiling kit do redo exhaust and head stud threads in alloy Suzuki cylinders. Once done, never a problem again.

 

Some may even be able to do it without removing the head if you need the car quick. The trick is to use a lot of grease to catch and contain the swarf produced from the drilling and tapping. Got to say though, this does have it's risks.

 

Naturally it is better to slip off the head first.

 

One good thing is that you'll never have any problems with plug threads ever again. A Helicoil is better than original and a lot cheaper than a replacement head. If you have the head off to do the job, have a good gander at the exhaust manifold threads and if they look at all dodgy, have those done too..

[jonah 1]

Going back to the original question... I think the only way the electrodes could have bent like that was if there was contact with the piston! Can't believe for one second that gas turbulance has done that. Shine a torch down the plug hole - can you see witness marks on the piston crown? Also in the top photo it looks like the centre electrode has mushroomed, which would back up the theory...

 

Shock from an impact from the piston could also have caused the threads to strip. The chuffing noise was probably gases escaping up past the spark plug. An inlet leak sounds more like a constant hissing noise, and the "sooting" you saw is probably just oil or grime, there's no reason you'd get soot near an inlet manifold leak (which just sucks in fresh air!).

 

Is it possible that the spark plugs were the wrong size (too long)??

[Rob_the_Sparky 9]

An idea,

 

I have seen in before the ceramic of a pulg to move relative tot he thread. Ponder if the ceramic has moved in rather than vica versa. Having said that it is a long shot as the onlt ones that I've seen have blown the centre out of the plug rather than pulling it in. (Centre on the lead, metal bit still in head!)

 

Rob

 

P.S. don't see how all 3 contacts could be bent without touching the centre electrode.

[maturin23 10]

I don't think you need to panic too much - taking the head off is a straightforward exercise for someone with a relatively ordered mind!

 

It's also an excuse to refresh (read 'upgrade') the cam, get a skim to raise compression a little, regrind the valve seats and perhaps put new oil seals in.

The parts are relatively cheap, and DIY labour is free...

 

Just a completely wild guess (and I've never heard of this happening before) but if the thread is totally shot could the plug have been 'sucked' a small way into the cylinder on an exhaust stroke and made contact with the piston?

Edited December 4, 2006 by maturin23

[Anthony 1,003]

Just get it helicoiled in-situ - Mattsav did this for me a while back on an 8v head and didn't cost much. Certainly considerably cheaper than buying new headbolts and headgasket, not to mention your time for removing and refitting the head.

[jonah 1]

I don't think you need to panic too much - taking the head off is a straightforward exercise for someone with a relatively ordered mind!

 

It's also an excuse to refresh (read 'upgrade') the cam, get a skim to raise compression a little, regrind the valve seats and perhaps put new oil seals in.

The parts are relatively cheap, and DIY labour is free...

 

Just a completely wild guess (and I've never heard of this happening before) but if the thread is totally shot could the plug have been 'sucked' a small way into the cylinder on an exhaust stroke and made contact with the piston?

No - the shoulder on the plug seats against a ledge in the plug bore so no way it can get sucked in. Besides, if the thread lets go then there's only one way the spark plug will want to move - and that's out, with considerable force! Same goes for the ceramic insulator - and that wouldn't explain how the outer electrodes got bent anyway.

 

If the plug tip really is meeting the piston then the last thing you want to do is skim the head!!

 

Will be interested to find out what's caused this...

 

Also, in that top photo, is there a chip missing from the thread??

Edited December 4, 2006 by jonah

[Anthony 1,003]

If the plug tip really is meeting the piston then the last thing you want to do is skim the head!!

I don't have an Mi head here in front of me to measure, but doesn't the spark plug sit high enough in the chamber that the piston would have decimated the valves and head before hitting the plug? Only way I can see is if a foreign object found its way into the chamber and the piston smashed that into the plug - as per Jonah's advice in his last post, I'd expect to see some tale-tale marks of this on the piston.

[DrSarty 90 1 Cars]

Update - head not off yet but will take her off this weekend. I did the engine swap (probably why it's gone wrong - but it was good whilst it lasted and the work is just a bind in this weather and doesn't phase me at all.

 

As I said, the head was gonna come off to upgrade the cam, drop the head via the copper head gasket & exahust anyway - but I didn't intend to do it in the cold. BUT, needs must and it's made me pull my finger out! (Incidentally PeterT will be providing an offset woodruff key for the cam pulley to compensate for the slight timing change caused by the head moving closer to the block).

 

I HAVE A NEW HEAD - (for the car ) I got it from Jonnie but as commented it cost a lot more than Helicoilling will. Anyway - everything will work out coz the head was professionally rally prep'd: skimmed, acid dipped, deburred and smoothed with triple cut & ground in valves. This head will have the exhaust cam fitted from the current head and the PeterT inlet cam fitted (15-18bhp Catcam equivalent in theory) when it goes back together in January with the Maniflow system.

 

This leaves me with a head, less exhaust cam only which I can sell pre OR post helicoilling: ANY INTERESTED PARTIES AT THIS STAGE???

 

When the old head comes off I'll get a better look at things and post a piccie here of anything relevant.

 

QUESTIONS: I'm inclined to agree that the plug couldn't have been hit, else the valves would've been whacked. We'll see if there's any damage. BUT what could've caused this please??? A weak mixture caused by an inlet leak as mentioned would make the plug run hot n'est pas? Detonation is caused by what and is what exactly? And why have the plug threads been damaged IF the plug wasn't struck?

 

Jonah - I agree that a hit IS a possibility here and inspecting the head complete and the piston crown will give a clearer indication. But again, if there's no debris or undesirable in the chamber, then why would a piston suddenly 'reach' a little higher UNLESS something horribily wrong's gone bad down below?

 

Will keep you posted - but thoughts (and offers for head if appropriate) please.

 

DrNOVROOMS

[Guest rick03054]

Is it possible that the threads were damaged when the plug was inserted, then after a bit of driving the fact that the plug was barely held in allowed it to drop down a bit into the cylinder, where is got whacked? Leaving the valves untouched.

[davev 1]

from having a closer look at the pics. to me it looks like something has hit the plug at the corner, pushing two electrods and the core over to the other. this could have also damaged the top thread as shown in the first pic. but that could have easily been done when putting it in.

 

id just check all the inlet tract for any missing parts(nuts/bolts) as i doubt anything could get past the air filter assuming ur running one.

 

dave.

[petert 587]

I've heard of spark plugs exploding out of Mi16 heads before haven't experienced it first hand. Theory is that the plug works loose, until it's only held by a few threads (note the colour of the last few threads in the pic.). Then when the cylinder pressure exceeds the shear force holding the threads, the plug gets blasted out. How the prongs got damaged exactly in your case, I'm really not sure. But that's my 2 cents!

 

I wouldn't trash, or give away cheaply, your head just becasue it has a damaged plug hole. As said earlier, helicoils are very successful and ultra reliable. I've done mains and cylinder bolt holes succesfully on Mi16 engines. Good Mi16 heads are becoming rarer. I personally wouldn't like to do a plug hole in situ., as swarf will enter the chamber. Depends on the engine age/quality/care factor I guess. You won't know the full story until the head comes off.

[jonah 1]

I haven't seen an Mi16 head up close so I don't know how far the spark plug normally protrudes into the chamber... if it's tucked well up in the combustion chamber then obviously there's no way the piston could reach it. But some other debris maybe (which could have also chipped the thread??)... suspect it will all become clear once the head's off!

 

All I'd add is that as soon as one one of those outer electrodes was touching the inner, then the plug was shorted out so it would have stopped sparking. So if all 3 are making contact, then either they were all bent at exactly the same instant, or they continued to bend even after ignition stopped in that cylinder. That's why I don't think it was gas turbulence that did it.