Spark Plug Insulation. - Dave
I have a cylinder on my single point injection 1.4 'K' series that is consitantly splitting spark plug insulation round the plug electrode.

1) According to the temp gague the engine doesn't run hot.

2) The split is clean and there is no sign whatsoever of overheating on the plug. (I'm told the isulation melts and distorts before it cracks due to heat)

3) The cylinder in question is one of the inner two.

4) My adjustment of the plug is fairly conventional - I don't think I'm bending the elctrode itself and physically splitting the insulation.

5) The plugs last about 1000 miles before a crack appears.

Any ideas??? I'll try running a slightly hotter plug next time but I'm told this makes very little difference...
Re: Spark Plug Insulation. - Andrew Bairsto
The only thing I can think of is that there is a waterway blocked in the area of that plug causing it to over heat (I have seen plenty of cracked plugs that have not melted).There is not much else in can be.How long has this been occuring ?
Re: Spark Plug Insulation. - Dave
Andrew Bairsto wrote:
>
> The only thing I can think of is that there is a waterway
> blocked in the area of that plug causing it to over heat (I
> have seen plenty of cracked plugs that have not melted).There
> is not much else in can be.How long has this been occuring ?

Yeah, that's all I could think off.

Hovever it's covered about 8000 miles in the last 6 months since the 'problem' reared it ugly head and the coolant is purest blue and showing no sign of any cause of a potential blockage.

I'd have thought it would have cooked it gasket by now if it was overheating too badly...

If it *is* split again I'll go to a hotter plug and better quality plugs than the cacky champions I usually buy and hope it goes away!
Re: Spark Plug Insulation. - Adam Going (Tune-Up Ltd)
Dave,
Certainly is an odd one this, if it is always the same cylinder. Localised overheating is a possibility, but I would go for the equivalent NGK or Bosch plug first.
Regartds, Adam
Re: Spark Plug Insulation. - John Slaughter
Dave

A bizarre story. However, if it is plug overheating, the last thing you want is a hotter plug. A hotter plug will do just that - run hotter. If that is the problem you need a colder plug. You certainly need to be sure the plugs are correct for the car.

The question of course is what's causing the cracking. Difficult to judge without seeing the plug. Could certainly be localised overheating, but you're quite right to say that this would make this plug look quite different to the other three. If it's mechanical damage is it something like carbon build up in the engine allowing the plug to be struck? As it's throttle body injection it isn't a faulty injector spraying onto the plug. The only other option I can think of is that is that the spark is choosing to run down the insulator, rather than jump to the earth electrode, so electrically machining a groove in the insulator - possible on one faulty plug maybe, but can't imagine why it should do it on the replacement, and I get the impression this is a recurring problem. Make sure the plug gaps are not too wide, as this could promote this. How about calling the plug manufacturers to see about sending a sample back to them for their opinion.

Regards

John
Re: Spark Plug Insulation. - Dave
John Slaughter wrote:

> Difficult to judge without seeing the plug. Could certainly
> be localised overheating, but you're quite right to say that
> this would make this plug look quite different to the other
> three.

All four come out identical... and all 4 look like a slightly cleaner version of the Haines Manual example of a plug out of a perfectly running engine. Except one has a hair line crack...

> If it's mechanical damage is it something like carbon
> build up in the engine allowing the plug to be struck?

It's not mechanical damage in situ. Whether I have an ununconcious habit of bending electrodes I don't know - I don't *think* I do - and you can imagine how much care is taken gapping plugs now...

> As
> it's throttle body injection it isn't a faulty injector
> spraying onto the plug. The only other option I can think of
> is that is that the spark is choosing to run down the
> insulator, rather than jump to the earth electrode, so
> electrically machining a groove in the insulator - possible
> on one faulty plug maybe, but can't imagine why it should do
> it on the replacement,

No sign of tracking either.

> and I get the impression this is a
> recurring problem.

Yep. Same cylinder.

> Make sure the plug gaps are not too wide,
> as this could promote this.

Interesting - I do leave the gaps too wide.

> How about calling the plug
> manufacturers to see about sending a sample back to them for
> their opinion.

Tempting a faulty batch of Champions could be the answer - I bought them all at the same time.

Thanks for the response!

Dave
Re: Spark Plug Insulation. - David Lacey
I manage the Service Dept of a busy Rover main dealer - we use NGK Spark Plugs and have never had one failure - I think we have used in excess of 1200 plugs since 01/01/01. All K Series engines with the exception of VVC models use NGK BKR6E plugs gapped 0.9mm and in some cases 1.1mm.
I think this is down to a plug problem although it is worth checking the servo hose as JK rightly says. I take it as it is a Single Point TBi model it is a fairly early model how many miles has it covered? Is the base CO% within limits? Should be 1% @ idle. My suggestion is (a)Set of NGK plugs (b)Full tune up
Best regards
Dave
Re: Spark Plug Insulation. - Dave
David Lacey wrote:
>
> I manage the Service Dept of a busy Rover main dealer - we
> use NGK Spark Plugs and have never had one failure -

Champions do have quite a bad reputation...

> I think
> we have used in excess of 1200 plugs since 01/01/01.

Jeeeze! All on that number two cylinder??? ;-)

> All K
> Series engines with the exception of VVC models use NGK BKR6E
> plugs gapped 0.9mm and in some cases 1.1mm.

Yeah, that was going to be my next step - switch to NGK. (Well I was gonna go for Bosche but you've convinced me...)

> I think this is down to a plug problem although it is worth
> checking the servo hose as JK rightly says. I take it as it
> is a Single Point TBi model it is a fairly early model how
> many miles has it covered?

120,000

>Is the base CO% within limits?

Dunno. Passed an MOT ok so the emmisions are legal - whether that's within tolerance I don't know...

> Should be 1% @ idle. My suggestion is

> (a)Set of NGK plugs

Will do!

> (b)Full tune up

I'm a little reluctant to spend cash on a tune-up that presumably involves a diagnostic machine at a Rover dealer.

Many thanks for the v. helpful advice!!!

Dave
Re: Spark Plug Insulation. - John Kenyon
I'm probably whistling through my a**e here, but have you tried checking the brake servo connection - air leaking in could be weakening the mixture causing that cylinder only to run hot?

/John
Re: Spark Plug Insulation. - Dave
John Kenyon wrote:
>
> I'm probably whistling through my a**e here, but have you
> tried checking the brake servo connection - air leaking in
> could be weakening the mixture causing that cylinder only to
> run hot?

Brilliant bit of lateral thinking! I'll have a look!!!
Re: Spark Plug Insulation. - Andrew Moorey (Tune-Up Ltd)
Bizzare! Does the engine "pink" under acceleration? This can cause mechanical damage as the mixture explodes under load instead of burning. One cylinder can be prone to detonation more than the others. The engine is fitted with a sensor to detect pinking (knocking) so shouldn't pink at all.
Good luck, keep us posted.
Andrew
Re: Spark Plug Insulation. - Dave
Andrew Moorey (Tune-Up Ltd) wrote:
>
> Bizzare! Does the engine "pink" under acceleration? This can
> cause mechanical damage as the mixture explodes under load
> instead of burning. One cylinder can be prone to detonation
> more than the others. The engine is fitted with a sensor to
> detect pinking (knocking) so shouldn't pink at all.
> Good luck, keep us posted.

No, no pinking.

In fact I haven't heard pinking in any car since I used to set the timeing on my old Skoda Estelle by advancing it till it knocked a bit and moving it back a fraction.

Happy days...

The main advice seems to be get a decent brand of plugs - which I'll do... I'll check the servo pipe too.

To be honest although it's in fairly good nick and runs great it only cost me 700 quid and has bravely taken a years abuse. I'm happy to change plugs every couple of months without bothering to to the root of this weird problem.
 

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