Spark plug destroyed

[kebabman 0]

Noticed I was getting a slight misfire at high revs recently, and last time it was down to plug fouling....so I whipped them out to give them a clean and look what came out of cylinder 6! This plug is less than 6 months old! :shock:

 

My theory is this, I know cylinder 6 burns a bit of oil, I'm presuming because the valve seals have perished. To me it looks like the plug has become heavily carbonised by oil deposits, and then over-heated causing the ceramic core to shatter. Sound plausible?

 

I presume having the stem seals replaced is an expensive job (head off)? It doesn't burn much oil really, and it runs fine and makes good power, so I was just going to put a higher heat-rated plug in and clean it regularly. Am I heading for a disaster by doing this? It runs surprisingly well on 5, maybe I should just remove the HT lead. :lol:

 

Mod edit: Pics resized

[kebabman 0]

Hmm that pic is a bit on the large side! Sorry :lol:

 

Andi - you should add the DHTML dynamic resize mod, it's only a few lines and it saves having to worry about big pics even when they're remote linked. ;)

[dr_mat 0]

Bit worrying, but maybe it was just a one-off failure? I'd just try another (genuine) plug and see what happens.

[kebabman 0]

I've stuck another NKG plug in there for the meantime, the other 5 look a bit worn but otherwise healthy (nice light hazey deposits). How much are genuine VW ones? Are they bi-electode like these? And do you think it'd make a big difference? Don't really want to shell out on 6 new plugs if I can help it.

[Kevin Bacon 5]

VW ones are platinum or nothing now.....£6 each

[Kevin Bacon 5]

BTW, your plugs can be analysed here:-

 

http://www.spark-plugs.co.uk/pages/tech ... gnosis.htm

 

Yours is a mixture of 'breakage' and 'deposits', which is oil and thermal expansion apparently!

[Roger Blassberg 0]

Generally, overheating is characterised by a white blistered ceramic insulator and is caused by over-advanced timing and / or weak fueling (please stop me if I'm teaching Grandma how to suck eggs). Oily plug is, as you say, either valve guides/seals or worn rings/bores. From the photos, it looks more sooty than oily, so perhaps there is just incomplete combustion going on, leading to a feeling of misfiring. You may have just had a defective plug - I would replace it, run it and see what happens before looking for more major trouble.

 

 

As you probably know, cylinders 1 and 6 are usually the first to show bore wear or ovalisation. Any smoke evident? You say that oil consumption isn't excessive - how much? How many miles has the engine done?

 

Actually you can change the valve stem oil seals with the head on by pressurising the cylinder with compressed air through the plug hole to hold up the valve - there's an adapter for the air line available from Sykes Pickavant or similar.

 

 

Best wishes

 

RB

[kebabman 0]

Thanks for the advice :)

 

It does sometimes blow a puff of smoke on downshifts when it's hot, but nothing on idle or when I just rev and release the throttle, it needs to be really hot to do it. In everday use I think it would be un-noticable, it doesn't smell of oil anyway. The engine has done 134k, it uses more than I'd like, but I have been doing quite a few trackdays where the engine spends a lot of time at high rpm...and to be honest I do rag the car most of the time, so I put it mainly down to my driving. I'd say it uses almost 1/2 a litre between fill-ups + 1 plastic can, i.e. ~400miles, and I'm running 10w40 Castrol GTX magnatec, although I haven't actually taken note...thats just what I think from when I remember having topped it.

 

There's no oil splattering on the back bumper though, and I do have a slight leak from the sump-pan gasket.

 

How much is it to get the valve seals done? Is there an easy way to determine if it's the valve seals, guides or piston rings?

[Reggit 0]

That sounds very similar to a plug failure I had the other month, a 2000 mile pulg had destroyed it's insulator and suddenly stopped firing. This was in number 6, and to cap it all I was only pootling along at the time!

I thing I have a photo of it somewhere, if I can find it I'll upload it so you can compare.

[dr_mat 0]

A pint every 400 miles? Jeez. At least you don't have to bother with oil changes, you'll have replaced every molecule of your oil twice over after 6000 miles of driving!!

I would go get some 15w40 semi-synthetic or even mineral oil and you should see that figure drop to something more sensible while you think about what to do next..

[kebabman 0]

I could've over-estimated that figure. What's the volume of oil between the max and min mark on the dipstick? I'll take some notes and work it out properly.

 

How much is a valve stem seal/guide refit? Is there a way to tell if it's the cylinder bore or the valve seals? Lastly, why has it only affected cylinder 6 and will it continue to make good power if I just keep the oil topped up?

 

I'm supposed to be doing Snetterton on the 29th of July, hope she'll be ok :?

[dr_mat 0]

~1 litre from max to min..

 

Head recondition weighs in at about £700-1000.

[RW1 0]

Is there a way to tell if it's the cylinder bore or the valve seals? Lastly, why has it only affected cylinder 6.

 

I'm supposed to be doing Snetterton on the 29th of July, hope she'll be ok :?

 

Generally if there is a puff of oil smoke on start up from over night standing, the valve seals are more the suspect. If it blows smoke out on the overrun at higher revs (+4,000rpm), the rings are worn. The test isn't conclusive so also do a compression test as well.

 

As said before, VR6s break rings quite often above 100k. I think with the plug going only in that cylinder, you have a broken piston ring. If the rings were generally badly worn then I would expect to see the other plugs to be similar.

 

Best to do a compression test if you can. It should show No. 6 down on compression significantly.

 

Obvioously with the engine apart, do the valve seals in the head as well, given the mileage the engine has done.

 

Snetterton. You'll be lucky to survive as the engine stresses will accelerate the problem. Sorree to spoil the fun but..... a little now will not be a major later.

[StormyTommy 0]

I've stuck another NKG plug in there for the meantime, the other 5 look a bit worn but otherwise healthy (nice light hazey deposits). How much are genuine VW ones?

I got 6 'BKR5EKUP', NGK, dual electrode, platinum, from http://www.spark-plugs.co.uk/

cost £45.40 inc, (postage free over £10)

Dealer quoted £60 inc for 6 NGK Platinum plugs, can't say they were the same because they couldn't quote NGK part #, just VAG #.

[Ady_G 0]

Hey kebabman

 

My VR6 does the same, mainly fouling 1 & 6 plugs, last time it was plug 6 but it takes about 5000 miles or about 10-12 months for it to get fouled up.

 

Last time I just cleaned them with a spark plug cleaner. I am suspecting worn valve stem seals as a very rare puff of smoke on idle or down change can be seen, similar to what you describe.

 

I also found Shell Helix or VW Quantum Silver lasts a lot longer than GTX, my VR6 drank GTX.

 

At the mo the car runs fine in everyway, so I'm a bit reluctant to spend a £1000 on a head rebuild to save a bit on plugs, which I normally replace every 12 months anyway.

 

Cheers

 

Ady

[Chris M 0]

here's a test for you'r rings,

 

with it up to running temp get some one to sit in and hold the revs at 3000rpm for 2-3mins, if the rings are worn it will blow clean at first then it will blue smoke after a min or so and gradually get worse depending how bad they are.

[kebabman 0]

Right, have reset the MFA2 to work out how much oil it's using, will report back, but I'm begginning to think I may have an oil leak somewhere. How much can valve stem seals leak?

 

Did the test holding it at 3000rpm and it didn't start smoking....so I guess the rings are ok? Also bought myself a gunman's compression tester from Halfrauds, and all cylinders gave 11Bar. Is this normal for a VR? (It was in the green section on the gauge so presume it's ok.)

 

Still going to run at Snetteron on the 29th as I've already paid up for it, Green Flag may be getting some business :lol:

 

Cheers for all the advice lads 8)

[dr_mat 0]

11 bar is around 130 psi, iirc, so that's pretty good.

[Roger Blassberg 0]

11 bar is around 130 psi, iirc,

 

Assume 1 bar=14.5 lbf/sq.in., so 11 bar(g) = 159.5 lbf/sq.in. above atmospheric.

 

Best wishes

 

RB

[dr_mat 0]

Ok I got the conversion factor wrong .. :)

The guy still has nothing to worry about, compression-wise ..

[kebabman 0]

Excellent. I presume to be sure I have to do a leak-down test, i.e. take the head off and fill the bores this oil and see if any seeps past the rings?

 

I think I'll leave that test for the moment if that's how it's done ;)

 

How much oil can a stem seal leak if a stem seal can leak oil?

[kebabman 0]

Just got back from Snetterton. I fappin love my Corrado, how many cars can you drive for 2.5 hours on the motorway, then hoon it around a track all day, and then drive home again in quiet comfort? Awesome.....and she didn't blow up! 8) (6 trackdays 134k and counting)

 

Although I did have to go to Halfrauds to buy some more pads, only ones they had cost £20, comedy brake fade after 1/2 a lap, still...what better way to bed them in than on the track? Good job the car was inpected by VOSA yesterday I think.. :lol: